Not sure what that veterinary word means? Look it up below!

Reprinted with permission from the University of California, Davis, The Book of Horses edited by Mordecai Siegal.

ABIOTROPHY:
Progressive loss of function of a tissue or organ.
ABNORMAL HOST:
A host infected with a parasite normally found in another host species.
ABSCESS:
A walled-off lesion filled with pus.
ACARIASIS:
General term for a mite infestation.
ACCOMMODATION:
Ability of the lens to change its shape in order to focus vision effectively on objects at different distances from the eye.
ACETABULUM:
The “cup” or “socket” portion of the hip joint.
ACETYLCHOLINE (ACh):
Messenger molecule released from axon terminals by a nerve impulse; responsible for transmission of the nerve impulse across the synaptic cleft to the muscle fiber supplied by the nerve.
ACETYLCHOLINESTERASE:
Enzyme capable of breaking down acetylcholine.
ACIDOSIS:
Systemic condition characterized by abnormally acid blood.
ACTIN:
A vital protein component of muscle, one of the proteins responsible for muscle contraction.
ACTINIC KERATOSES:
Single or multiple, firm, elevated, plaque- or papulelike skin lesions that result from excessive exposure to sunlight; considered to be precancerous lesions.
ACTINOMYCOSIS:
Pus-producing diseases caused by bacteria of the genus Actinomyces.
ACTIVE IMMUNIZATION:
Vaccination.
ACUTE:
Of short duration and relatively severe; having a rapid onset.
ADDISON’S DISEASE:
Hypoadrenocorticism; insufficient secretory activity by the adrenal cortex.
ADENOCARCINOMA:
Any malignant tumor originating in glandular tissue.
ADENOMA:
Any benign tumor originating in glandular tissue.
ADENOSINE TRIPHOSPHATE (ATP):
The major form of energy used by cells in the body.
ADHESION:
A fusion or sticking together of surfaces.
ADIPSIA:
The absence of thirst; avoidance of drinking.
ADJUVANT:
Substance that nonspecifically stimulates immune responses; used in inactivated vaccines to prolong the immune response to vaccine components.
ADJUVANT CHEMOTHERAPY:
Use of anticancer drugs following surgical or radiation treatments in an effort to destroy residual (microscopic) tumor cells that may have been left behind.
ADRENAL CORTEX:
The outer layer of the adrenal glands.
ADRENAL GLANDS:
Glands located adjacent to the kidneys, involved in the secretion of several important hormones including cortisol, corticosterone, aldosterone, and epinephrine (adrenaline).
ADRENALINE (EPINEPHRINE):
A hormone secreted by the adrenal glands; it acts to increase blood sugar levels and blood pressure and to accelerate the heart rate.
ADRENOCORTICOTROPIC HORMONE (ACTH):
A hormone produced by the pituitary gland in the brain; it exerts a controlling function over the cortex (external portion) of the adrenal glands.
ADSORB:
To bind to a surface.
ADULTICIDE:
Medication to kill adult worms.
AEROBIC:
Requiring the presence of oxygen to grow.
AEROSOL EXPOSURE:
Exposure to an infectious agent by means of contaminated moisture droplets drifting in the air.
AEROSOL THERAPY:
Treatment in which drug therapy (antibiotic or other compound) is delivered by misting or spraying the drug into the airways, usually by means of a funnel or cone placed over the nose; useful in treating pneumonia and certain other respiratory ailments. Also called NEBULIZATION.
AFRICAN HORSE SICKNESS:
Acute, severe to mild, insect-transmitted disease characterized by fever and signs of cardiac or pulmonary insufficiency; caused by an orbivirus in the Reoviridae family of RNA viruses.
ALANINE AMINOTRANSFERASE (ALT, SGPT):
A liver-cell enzyme; increased levels in the bloodstream are indicative of liver-cell injury.
ALBUMIN:
A major protein component of the blood plasma, important in maintaining osmotic pressure within the blood vasculature and as a transport protein for many substances.
ALDOSTERONE:
A hormone secreted by the adrenal cortex; important in the regulation of sodium and potassium levels and, in turn, in retaining water within the body.
ALGAE (singular: alga):
Single-celled organisms that include seaweed, many fresh-water plants, and certain opportunistic pathogens such as Prototheca.
ALLELE:
An alternative form of a given gene. For each gene there are two alleles, one on each chromosome of a chromosome pair. One allele is inherited from the mother, the other from the father.
ALLERGEN:
Any substance that can induce an allergic reaction.
ALLERGENIC:
Inducing allergy.
ALLERGIC BRONCHITIS:
Allergic inflammation of the bronchi.
ALLERGIC CONTACT DERMATITIS:
An uncommon skin disease caused by a hypersensitivity reaction, as occurs in hikers and backpackers following contact with poison ivy or poison oak.
ALLERGY:
A hypersensitive state of the immune response, wherein exposure to a particular substance (an allergen) results in a noxious and sometimes physically harmful immunologic response.
ALLOGRAFT:
Tissue graft obtained from an individual of the same species as the recipient.
ALOPECIA:
Absence or loss of hair.
ALVEOLI (singular: alveolus):
Small air sacs comprising the innermost structure of the lungs. It is through the delicate walls of the alveoli that gas exchange occurs between the blood (flowing through the pulmonary capillaries) and the inhaled or exhaled air.
AMBULATORY:
Involving locomotion; able to walk.
AMINO ACIDS:
Nitrogen-containing molecules that form the structural backbone of proteins. All amino acids contain both an amino group (NH2) and a carboxyl group (COOH).
AMMONIA:
A waste product of protein metabolism; normally excreted through the kidneys.
AMNION:
The placental membrane immediately surrounding the foal.
AMYLASE:
Enzyme produced by the salivary glands and pancreas that breaks down carbohydrates.
AMYLOID:
An insoluble protein substance that causes disease (amyloidosis) when deposited in large quantities in tissues.
AMYLOIDOSIS:
Disease process characterized by deposition of amyloid in various tissues of the body, including the kidneys.
ANABOLISM:
The body’s conversion of simple substances to more complex compounds.
ANAEROBIC:
Able to grow in the absence of oxygen.
ANAGEN:
The phase of hair follicle activity during which hair is actively being produced.
ANAL SPHINCTER:
The circular band or ring of muscle that controls the release of feces from the anus.
ANALGESICS:
Pain-killing medications.
ANAMNESTIC RESPONSE:
Immunologic memory; the ability of the immune system to “remember” a foreign substance to which it has been exposed, and to produce an even more effective response to it upon subsequent reexposure.
ANAPHYLACTIC REACTION (ANAPHYLAXIS):
A rapidly developing, exaggerated (and sometimes life-threatening) allergic reaction.
ANATOMY:
The study of body structure.
ANDROGEN:
Male sex hormone; e.g., testosterone.
ANEMIA:
Low red blood cell count, reduced hemoglobin levels, or reduced volume of packed red cells.
ANESTRUS:
The sexually inactive period between two estrus cycles.
ANGIOEDEMA:
Recurrent wheals or welts in the skin, caused by dilation and/or increased permeability of capillaries.
ANGIOGRAPHY:
The radiographic visualization of blood vessels, accomplished by the intravenous injection of a contrast medium that allows the shape and course of the vessels to be delineated on X-ray examination.
ANGIOSARCOMA:
Tumor of blood or lymphatic vessels.
ANKYLOBLEPHARON:
Failure of one or both eyelids of the newborn to open at the appropriate time.
ANKYLOSIS:
The immobility and consolidation of a joint, secondary to trauma, infection, or surgery.
ANNULAR LIGAMENTS:
Ligaments that function to maintain tendon alignment where the tendons cross a joint.
ANORECTIC:
Having no appetite.
ANOREXIA:
Loss of appetite; inappetence.
ANTEMORTEM:
Before death.
ANTERIOR CHAMBER:
The fluid-filled space at the front of the eye, situated between the cornea and the iris.
ANTERIOR UVEA:
The iris and ciliary body of the eye.
ANTERIOR UVEITIS:
Inflammation of the iris and ciliary body of the eye.
ANTHELMINTIC:
Any deworming medication.
ANTHRAX:
A rapidly fatal illness caused by multiplication and spread of the bacterium Bacillus anthracis following ingestion of the bacterial spores.
ANTIBIOTIC:
A chemical substance produced by microorganisms that is capable of inhibiting or killing other microorganisms; many antibiotics are used medically for the treatment of serious bacterial infections. Examples of antibiotics include penicillin, tetracycline, and gentamicin.
ANTIBIOTIC SENSITIVITY TESTING:
Laboratory test procedure for identifying the sensitivity or resistance of a bacterial isolate to several antibiotics.
ANTIBODIES (IMMUNOGLOBULINS):
Specialized proteins produced by cells of the immune system in response to the presence of foreign material (bacteria, viruses, toxins, etc.); antibodies are capable of binding to the foreign material and thus alerting other immune cells to its presence.
ANTICOAGULANT:
Chemical that prevents blood from clotting.
ANTIDIURETIC HORMONE (ADH):
Pituitary gland hormone that controls water resorption by the kidneys, urine production and concentration, and water balance; also called vasopressin.
ANTIEMETICS:
Medications for controlling vomiting.
ANTIFUNGAL:
A chemical substance produced by microorganisms or by other means, useful in the treatment of fungal infections.
ANTIGEN:
A substance capable of inducing a specific immune response in the body, by binding to a specific antibody; can be a property of bacteria, viruses, other foreign proteins, or even host tissue cells.
ANTIGENIC:
Having the properties of an antigen.
ANTIMICROBIAL:
Killing or suppressing the growth of microorganisms; also, any antibiotic or antifungal medication.
ANTINUCLEAR ANTIBODY (ANA) TEST:
Test that detects autoantibodies against the DNA of cell nuclei; used as an aid in the diagnosis of systemic lupus erythematosus (SLE, lupus).
ANTIOXIDANTS:
Substances such as vitamin E and selenium that protect cells against damage caused by by-products of normal metabolic processes.
ANTISERUM:
Serum that contains high levels of antibodies specific for a particular antigen of interest.
ANTISPASMODICS:
Medications to prevent spasms of the gastrointestinal tract.
ANTITUSSIVES:
Cough suppressants.
ANURIA:
Complete cessation of urine production.
AORTA:
The great vessel arising from the left ventricle of the heart, that feeds blood through the arterial system into the body.
AORTIC STENOSIS:
Constriction (abnormal narrowing) of the connection between the left ventricle and the aorta.
AORTIC VALVE:
The semilunar valve on the left side of the heart; also called the aortic semilunar outflow valve.
APLASIA:
Imperfect development or absence of a tissue or organ.
APNEA:
Cessation of breathing.
APOCRINE CYST:
Cyst caused by obstruction of a sweat gland.
APOCRINE SWEAT GLANDS:
Sweat glands that empty their contents into an associated hair follicle.
APPENDICULAR SKELETON:
That portion of the skeleton composed of the bones forming the limbs and pelvis.
AQUEOUS HUMOR:
The fluid occupying the anterior and posterior chambers of the eye.
ARABIAN FADING SYNDROME:
Juvenile Arabian leukoderma.
ARACHIDONIC ACID:
An essential fatty acid found in animal fats; a precursor in the biosynthesis of compounds such as the prostaglandins.
ARBORIZE:
To branch.
AREA CENTRALIS:
Specialized area of the retina, near the optic disc, that possesses an abundance of cone photoreceptors and is largely responsible for the most precise and accurate vision.
ARGASID TICKS:
Soft-bodied ticks; distinguished from ixodid (hard-bodied) ticks.
ARRHYTHMIA:
Any abnormal irregularity of the heartbeat caused by an electrical disorder in the heart.
ARTERIES:
Thick, muscular vessels that drive oxygenated blood from the heart toward the tissues.
ARTERIOLES:
Small arteries.
ARTERITIS:
Inflammation of an artery.
ARTHRITIS:
Joint inflammation.
ARTHROPATHY:
Any joint disease.
ARTHROPOD:
An invertebrate organism with a hard outer skeleton (exoskeleton) and a segmented body; examples include insects, spiders, and crustaceans.
ARTHROSCOPIC SURGERY:
Surgery using a tubular instrument (arthroscope) for examining and carrying out surgical procedures within a joint, without the need for an extensive incision.
ARTHROSPORES:
Infective units of the filamentous mold form of the fungal pathogen Coccidioides immitis, the cause of coccidioidomycosis (“valley fever”).
ARTICULAR CARTILAGE:
Cartilage found within joint structures.
ARTICULATE:
To connect at a movable joint.
ASCARIASIS:
Any ascarid infestation.
ASCARID:
A type of roundworm.
ASCITES:
The accumulation of fluid within the abdominal cavity.
ASCORBIC ACID:
Vitamin C.
ASPARTATE AMINOTRANSFERASE (AST, SGOT):
A liver-cell enzyme that is also found in muscle cells and red blood cells.
ASPERMOGENESIS:
Failure to produce sperm.
ASPHYXIA:
Suffocation.
ASPIRATE:
The removal of fluid from a tissue or cavity by means of a syringe and needle.
ASPIRATION PNEUMONIA:
Pneumonia caused by accidental inhalation of food or other material into the lungs.
ASPIRATION SMEAR:
Diagnostic procedure in which fluid, containing cells, is withdrawn from a tissue or body cavity and then smeared onto a glass microscope slide for examination.
ASYMPTOMATIC:
Not exhibiting clinical signs.
ATAXIA:
Incoordination.
ATHEROSCLEROSIS:
Vascular disease associated with high blood pressure and high cholesterol and fats in people; exceptionally rare in animals.
ATOPIC DERMATITIS:
Heritable hypersensitivity to pollens or other environmental allergens, which results clinically in immunologic and inflammatory reactions in the skin.
ATOPY:
An inherited predisposition toward the development of allergy.
ATRESIA:
Congenital absence or occlusion of an orifice or tubular organ.
ATRIAL FIBRILLATION:
Arrhythmia characterized by irregular, disorganized, chaotic changes in the electrical activity of the upper chambers of the heart, resulting in abnormal contractions.
ATRIAL SEPTAL DEFECT:
Rare congenital defect characterized by the presence of a hole in the wall or septum separating the left and right atria of the heart.
ATRIOVENTRICULAR (AV) NODE:
The heart region electrically connecting the atria and ventricles; it slows the conduction of the depolarization wave so that a short period of time is interposed between atrial and ventricular contractions.
ATRIOVENTRICULAR (AV) VALVES:
The heart valves that separate each atrium from its corresponding ventricle
ATRIUM (PLURAL: ATRIA):
One of the two upper chambers of the heart.
ATROPHY:
Shrinking or wasting of a tissue or organ.
ATROPINE:
An alkaloid drug that relaxes smooth muscle, increases the heart rate, and in the eye causes dilation of the pupil.
AUDITORY OSSICLES:
Tiny bones in the middle ear that are responsible for transmitting the vibrations of the eardrum to the inner ear.
AURAL FLAT WARTS (AURAL PLAQUES):
Skin warts found on the ears of horses greater than a year of age; caused by a papillomavirus.
AUSCULT, AUSCULTATE:
To listen to the inner sounds of the chest or abdomen with the aid of a stethoscope.
AUTOANALYZERS:
Automated equipment for performing serum chemistry panels.
AUTOANTIBODY:
An antibody directed against “self,” i.e., against the body.
AUTOIMMUNE RESPONSE:
An inappropriate immune response, directed against the body’s own tissues.
AUTONOMIC NERVOUS SYSTEM:
That part of the nervous system involved in the regulation of the heartbeat, glandular secretions, and smooth muscle contraction and relaxation, and generally not subject to conscious control.
AUTONOMOUSLY:
Uncontrollably.
AUTOSOMAL:
Referring to any of the chromosomes excluding the sex chromosomes.
AVERSION CONDITIONING:
Learned avoidance of unpleasant situations, such as an encounter with an electric fence.
AVIDIN:
A constituent protein of egg whites that can impair absorption of the vitamin biotin.
AVULSION:
A pulling or tearing away.
AXIAL SKELETON:
That portion of the skeleton composed of the skull, vertebrae, ribs, and sternum (breastbone).
AXILLARY NODULAR NECROSIS:
Uncommon, sporadic skin disease characterized by the development of nodules in the axillary region (“armpit”).
AXON:
The fingerlike extension of a nerve cell, along which the nerve impulse travels.
AXON TERMINALS:
Branchings of a nerve axon within muscle, forming neuromuscular junctions with the myofibers supplied by the nerve.
AZOTEMIA:
An elevation of blood urea nitrogen (BUN) and creatinine levels in the bloodstream.
B LYMPHOCYTES (B CELLS):
Lymphocytes that upon proper stimulation by an antigen transform into plasma cells, which produce antibody to the antigen.
BABESIOSIS:
Any of several diseases caused by protozoa of the genus Babesia.
BACILLUS CALMETTE-GUERIN (BCG):
A live, avirulent bacterial cell preparation of the bovine tuberculosis organism, Mycobacterium bovis; useful for immunizing people against tuberculosis and for nonspecifically stimulating the immune system.
BACTEREMIA:
Presence of bacteria in the bloodstream.
BACTERIA (SINGULAR: BACTERIUM):
Minute, single-celled organisms ubiquitous in the environment; they contain a cell wall and a nucleus lacking a delimiting membrane, and divide by binary fission (the parental cell dividing into two approximately equal daughter cells).
BACTERIAL ENDOCARDITIS:
Inflammation of the lining of the heart, caused by bacterial infection of one or more heart valves.
BACTERIN:
Any killed bacterial vaccine.
BACTERIOLOGY:
The study of bacteria.
BALANITIS:
Inflammation of the penis.
BALANOPOSTHITIS:
Inflammation of the penis and prepuce.
BARIUM:
Metallic element commonly used as a contrast medium in radiology, particularly useful for examining disorders of the gastrointestinal tract. The barium is first swallowed by the patient and X-ray films are then taken. The general structure and movements of the gastrointestinal tract become visible owing to the inability of the X-ray beam to penetrate the contrast medium.
BASAL CELL LAYER:
The bottom cell layer of the epidermis (the outermost layer of the skin).
BASAL CELL TUMOR:
Benign tumor of basal cells, present in the basal cell layer of the epidermis (the outermost layer of the skin).
BASIDIOBOLOMYCOSIS:
A form of phycomycosis caused by Basidiobolus; occurs only rarely in the United States.
BASOPHIL:
A specialized white blood cell containing histamine and serotonin.
BASOPHILIC:
Staining dark blue.
BEAN:
Common term for urethral diverticular concretion.
BENCE-JONES PROTEINS:
Immunoglobulins or immunoglobulin fragments detected in blood and sometimes urine in patients with multiple myeloma.
BENIGN:
Not malignant; a tumor that is not cancerous (i.e., will not spread).
BETA BLOCKERS:
Drugs that block beta-adrenergic nerve impulses; important in treating tachycardias (abnormally rapid heart rates).
BETA CELLS:
Cells within the islets of Langerhans in the endocrine pancreas; they are the source of the hormone insulin.
BICIPITAL BURSITIS:
Inflammation of the bicipital bursa, located underneath the biceps tendon.
BIG HEAD:
Colloquial term for nutritional secondary hyperparathyroidism.
BILATERAL:
Occurring on both sides.
BILATERALLY SYMMETRICAL:
Occurring simultaneously in approximately the same place on each side of the body.
BILE:
Fluid produced by the liver and deposited in the small intestine through the bile ducts, for the purpose of aiding the digestion of nutrients.
BILE ACIDS:
Steroid acids made from cholesterol, they are components of bile.
BILE DUCT:
Duct that discharges digestive fluids (bile) from the liver into the small intestine.
BILIRUBIN:
A yellow bile pigment, a breakdown product of recycled hemoglobin from red blood cells; the pigment causing jaundice.
BINARY FISSION:
Method of bacterial and protozoal multiplication wherein the parental cell divides into two approximately equal daughter cells.
BINOCULAR FIXATION:
The ability, particularly well developed in primates, to focus both eyes on a single object.
BIOLOGICAL RESPONSE MODIFIERS:
Substances such as the interferons and the interleukins that modify immune responses.
BIOLOGICAL VECTOR:
A vector in which a developmental stage of a particular parasite necessarily occurs.
BIOPSY:
The procedure by which a small sample of tissue is obtained for microscopic examination or culture, for the purpose of making a medical diagnosis.
BLASTOCYST:
An early stage of the developing embryo.
BLEPHARITIS:
Inflammatory disease of the eyelids.
BLEPHAROSPASM:
Spasm of the eyelid musculature, causing squinting.
BLIND SPOT:
That portion of the visual field behind the line of sight, that cannot be seen without changing eye and head position.
BLIND STAGGERS:
Common name for leukoencephalomalacia.
BLOAT:
Distension of the stomach.
BLOOD:
The fluid and its component cells, that circulate through the blood vessels and carry oxygen and other nutrients to body cells.
BLOOD PLASMA:
The liquid fraction of the blood (as opposed to blood cells).
BLOOD SMEAR:
A thin layer of blood smeared on a glass slide, stained, and viewed under a microscope; used to identify the maturity and type of blood cells present and to detect any abnormalities of those cells.
BLOOD UREA NITROGEN (BUN):
A measure of the nitrogenous waste products circulating in the blood; elevated levels are usually indicative of kidney malfunction.
BLOOD VESSELS:
Arteries, arterioles, veins, venules, capillaries: the conduits for the transport of blood throughout the body.
BLOOD-TYPING:
Laboratory procedure by which the red blood cells in a blood sample are identified as belonging to one of several blood groups.
BOG SPAVIN:
Chronic swelling of the upper joint of the hock; most commonly caused by osteochondritis dissecans (OCD).
BOIL:
A deep-seated bacterial infection of a hair follicle, producing a painful skin nodule containing pus; also called a furuncle.
BONE MARROW:
The soft inner tissue of bones, containing the blood-forming elements (precursor cells of the red and white blood cells and blood platelets) of the circulatory system.
BONE PLATING:
Method of fracture repair wherein the bone fragments are replaced in their original location and held in place with a perforated metal plate (bone plate), which is attached to the fragments with small screws.
BONE SPAVIN:
Degenerative arthritis of the lower joints of the hocks; the most common cause of hindlimb lameness in horses.
BONY ORBIT:
The bones of the skull that house and protect the eyeball.
BOOSTER:
Any dose of vaccine given subsequent to the initial dose, or subsequent to natural exposure, and designed to maintain the immune state or improve it.
BORBORYGMUS:
Gurgling noises caused by the rapid movement of gas through the intestines.
BORNA DISEASE:
Rare, highly fatal disease of horses and sheep in Germany and Switzerland; caused by an RNA virus that thus far has proved extremely difficult to characterize or classify.
BOTRYOMYCOSIS:
Type of wound infection caused by Staphylococcus aureus that occurs following trauma; common sites include the lower extremities and scrotum.
BOTS:
The larvae of hairy, beelike flies of the genus Gasterophilus; they are often found in the stomach of the horse.
BOTULINAL TOXIN:
The neurotoxin produced in botulism.
BOTULISM:
A rare disease caused by a neurotoxin produced by the bacterium Clostridium botulinum; it targets the neuromuscular nerve endings, producing a flaccid paralysis.
BRACHYGNATHISM:
Condition wherein the lower jaw is shorter than the upper jaw, placing the lower incisor teeth farther behind the upper incisor teeth.
BRACHYTHERAPY:
Radiation therapy technique wherein a radioactive device is inserted into a tumor and left in place for a period of time, during which the radiation slowly kills the tumor cells.
BRADYCARDIA:
Abnormally slow heart rate.
BRADYZOITES:
Dormant, encysted forms of the parasite Toxoplasma gondii.
BRAIN STEM:
Portion of the brain containing nerve centers that control the heart rate, respiratory rate and pattern, and level of consciousness.
BRAN DISEASE:
Generalized disorder caused primarily by a deficiency of calcium in the diet in the face of a phosphorus excess.
BREAKDOWN INJURY:
Rupture of the suspensory apparatus, i.e., loss of one or more supporting structures of the fetlock.
BREECH PRESENTATION:
Birth in which the fetus is delivered rear-end first.
BROKEN WIND:
Common name for chronic obstructive pulmonary disease.
BRONCHI:
The larger air passages leading from the trachea and branching within the lungs.
BRONCHIOLES:
Smaller branches of air passages leading from the bronchi to the alveoli (the small air sacs within the lungs, through the walls of which gas exchange between the blood and air occurs).
BRONCHOCONSTRICTION:
Narrowing of the larger airways.
BRONCHODILATORS:
Drugs that cause expansion of vital airways in the lungs, allowing for improved respiration.
BRONCHOPNEUMONIA:
Lung inflammation that is initiated within the bronchioles.
BRONCHOSCOPY:
Endoscopic examination of the trachea and bronchi.
BUCKED SHINS:
Painful condition caused by inflammation and hemorrhage over the front surface of the cannon bone; a common injury of 2- and 3-year-old race horses.
BUDDING:
Form of asexual reproduction in certain protozoa wherein a dividing cell divides into two unequal parts, the larger part being considered the parent and the smaller one the bud.
BULBOURETHRAL GLANDS:
Glands that produce the fluid portion of the semen.
BULLA:
A large vesicle.
BULLOUS PEMPHIGOID:
A very rare autoimmune skin disease characterized by the production of autoantibodies and the development of vesicles and bullae beneath the epidermis.
BUPHTHALMOS:
Gross enlargement of the eyeball.
BURSA:
Fluid-filled sac or saclike cavity, situated over pressure points in tissues where friction from repeated movement might develop.
BURSITIS:
Inflammation of a bursa.
BUTTRESS FOOT:
An advanced form of degenerative arthritis, caused by new bone growth in the region of the extensor process of the coffin bone.
CACHEXIA:
Seriously poor health; malnutrition and wasting.
CAESAREAN SECTION:
Delivery of a fetus by surgically removing it from the uterus.
CALCANEUS:
Heel bone.
CALCIFICATION CENTERS:
Areas of bone deposit and change within bone tissue.
CALCITONIN:
A calcium-regulating hormone produced by the thyroid gland.
CALCIUM CHANNEL BLOCKERS:
Drugs useful in treating tachycardias (abnormally rapid heart rates).
CALCULOGENIC:
Stone-forming.
CALCULUS (PLURAL: CALCULI):
Dental tartar, the mineralized concretions of salivary calcium and phosphorus salts and tooth-surface plaque; also, a urinary stone.
CALORIE:
Unit defined as the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius (centigrade). However, the larger kilocalorie is usually referred to as a “calorie” in the nonscientific community.
CANCELLOUS BONE:
Bone tissue having a spongy or latticelike internal structure; an example is the bone marrow.
CANCER:
The general term for any malignant tumor.
CANDIDIASIS:
A relatively uncommon infection of skin and mucous membranes of the oral cavity, respiratory tract, and genital area of horses, caused by yeast of the genus Candida.
CANKER:
Chronic overgrowth of the horn-producing tissues of the foot, occurring most commonly in horses housed under unsanitary conditions.
CANNON BONE:
The third metacarpal bone, above the fetlock joint.
CANNON KERATOSIS:
Seborrhea affecting the front surface of the rear cannon bone.
CANNULA:
A tube inserted into a duct or body cavity, for the purpose either of infusing or removing fluid.
CANTHARIDIN:
The toxin in blister beetles responsible for blister beetle poisoning in horses.
CAPILLARIES:
The smallest blood vessels. They permeate the tissues, serving as microscopic extensions of arterioles and venules; through their semipermeable walls, fluids, nutrients, and waste gases are exchanged between the blood and the tissues.
CAPPED HOCK:
Traumatic bursitis over the point of the hock, usually caused by the horse’s kicking a solid structure.
CAPS:
Remnants of deciduous premolar teeth that are left behind when the permanent premolars erupt.
CARBUNCLE:
A deep-seated skin infection containing many pockets of pus.
CARCINOGEN:
Any cancer-causing substance, such as asbestos, nickel, alcohol, or tobacco.
CARCINOMA:
A cancer (malignant tumor) of epithelial cells.
CARDIAC:
Pertaining to the heart.
CARDIAC ARREST:
Cessation of the heartbeat.
CARDIAC CATHETERIZATION:
The passing of a catheter through a peripheral blood vessel and inside the heart, either for diagnostic or therapeutic purposes.
CARDIAC INSUFFICIENCY:
Heart failure.
CARDIAC MUSCLE:
Specialized type of muscle found only in the heart.
CARDIAC TAMPONADE:
Acute compression of the heart, caused by filling of the pericardial sac with fluid or blood.
CARDIAC ULTRASOUND:
Examination of the heart by means of ultrasonic sound waves, for the purpose of disease diagnosis; also known as echocardiography.
CARDIOGENIC SHOCK:
Shock caused by a diseased heart that has become so dysfunctional that it can no longer pump sufficient blood to the body.
CARDIOMYOPATHY:
Enlargement of the heart, caused either by a thickening or thinning of the heart muscle.
CARDIOPULMONARY BYPASS:
Open-heart surgery wherein a heart-lung machine oxygenates and pumps blood while the heart is stopped.
CARDIOVASCULAR SYSTEM:
The heart and blood vessels of the body.
CARNIVORES:
Meat eaters.
CARPAL CANAL SYNDROME:
Annular ligament constriction on the back side of the carpus, causing lameness.
CARTILAGE:
Specialized connective tissue especially important in bone growth and the formation of joints.
CASLICK’S OPERATION:
Surgical procedure to decrease the aspiration of air and contaminants into the female reproductive tract.
CASTRATION:
Surgical removal of the testes; sterilization of the male.
CASTS:
Solid, tubular deposits in the urine, usually cast off from the walls of kidney tubules.
CATABOLISM:
The body’s breakdown of complex molecules, such as protein and fat, to simpler compounds.
CATARACT:
Lens opacity in the eye, affecting vision.
CATECHOLAMINES:
Compounds secreted by the adrenal medulla, the most notable of which is epinephrine (adrenaline).
CATHARTICS:
Drugs to induce evacuation of the bowel.
CATHETER:
A flexible tubular instrument for insertion into a blood vessel or body cavity.
CAUDA EQUINA:
The nerve roots at the termination of the spinal cord.
CAUDAL:
To the rear of; toward the tail.
CECUM:
The first segment of the large intestine, consisting of a large dilated pouch.
CELL:
The most basic functioning unit of living organisms, composed of a nucleus, cytoplasm, organelles, and other constituents. Cells are the fundamental building blocks of tissues and in their nuclei contain all the genetic information necessary for the growth and differentiation of a complete organism.
CELLULAR (CELL-MEDIATED) IMMUNE RESPONSE:
The mounting of a cytotoxic T cell/macrophage/natural killer (NK) cell immune response to an antigen.
CELLULAR DIFFERENTIATION:
The process by which cells mature into specialized, fully functioning units.
CELLULITIS:
Diffuse inflammation resulting from (usually bacterial) infection of deep connective tissue, sometimes forming an abscess.
CEMENTUM:
Specialized type of connective tissue that covers the tooth roots.
CENTRAL NERVOUS SYSTEM (CNS):
The brain and spinal cord.
CENTRIFUGE:
To spin in order to separate the light and heavier particulates in a fluid sample; a machine for performing this procedure.
CERCARIA:
Tadpolelike larval form of flukes that arises from the redia stage.
CEREBELLAR ABIOTROPHY:
Inherited disorder seen in some Arabian family lines, characterized by a progressive loss of neurons in the cerebellum.
CEREBELLAR HYPOPLASIA:
Underdevelopment of the cerebellum, manifested clinically by incoordination.
CEREBELLUM:
Portion of the brain concerned with motor function, balance, and the coordination of movement.
CEREBROSPINAL FLUID (CSF):
Fluid bathing the surfaces of the brain and spinal cord.
CEREBRUM:
Portion of the brain concerned with conscious thought, perceptions, and learned skills.
CERUMINOUS GLANDS:
Glands that produce the waxy coating of the ear canal.
CERVICAL:
Pertaining to the neck.
CERVICAL SPONDYLOSIS:
Degenerative and proliferative disease of the neck vertebrae.
CERVIX:
Oval-shaped mass in the female reproductive tract whose opening connects the uterus with the vagina.
CESTOCIDAL:
Able to kill tapeworms.
CESTODES:
Tapeworms; internal parasites having a head unit (scolex) and numerous body segments (proglottids).
CHEEKTEETH:
General term for the premolar and molar teeth.
CHEMOSIS:
Excessive swelling of the conjunctiva (membranes covering the inner surface of the eyelids).
CHOKE:
Physical obstruction of the esophagus.
CHOLINE:
A B vitamin important for proper function of the nervous system and for preventing fat deposition in the liver.
CHONDROIDS:
Pus in the guttural pouch that, over time, has becomed thickened into variously sized, cheesy concretions.
CHONDROSARCOMA:
A malignant tumor of cartilage.
CHORIORETINITIS:
Inflammation of the choroid and retina of the eye.
CHOROID:
Thin, pigmented middle layer of the eye containing nerves and blood vessels; it supplies blood to the retina.
CHROMOSOMES:
The very large and complex molecules of DNA that occur in the nucleus of every cell and that carry the genetic information needed to make every protein in the body.
CHRONIC:
Long-term; of lengthy duration; persisting over a long period.
CHRONIC CARRIER STATE:
Situation in which an animal or human being maintains (carries) an infectious disease agent for a prolonged period of time.
CHRONIC INTERSTITIAL NEPHRITIS:
Chronic, progressive destruction of the kidneys, marked by a reduction in kidney size and scarring of kidney tissue.
CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD):
Term referring to a number of conditions leading to chronic or recurrent obstruction of airflow within the lung; also called heaves or broken wind.
CHRONIC PHARYNGEAL LYMPHOID HYPERPLASIA (CPLH):
An abnormal increase in size of the lymphocyte-rich tissues lining the pharynx, analogous to tonsillitis of children; also referred to as chronic pharyngitis or follicular pharyngitis.
CICATRIZATION:
Scar-tissue formation.
CILIA (SINGULAR: CILIUM):
Minute, hairlike cellular processes lining much of the respiratory tract; their rhythmic beating movements, in concert with an overlying layer of mucus, effect removal of debris and other foreign material from the airways.
CILIARY BODY:
The circular muscle located directly behind the iris of the eye.
CIRRHOSIS:
Liver disease characterized by replacement of functioning liver cells by scar tissue.
CLASSICAL CONDITIONING:
The association between a stimulus and a response.
CLEFT PALATE:
Birth defect characterized by an abnormal connection between the oral cavity and the nasal cavity; as a result, small amounts of milk often may be seen dripping from the nostrils when the foal suckles.
CLITORIS:
Small mound of erectile tissue in the female reproductive tract; the female analog of the male penis.
CLUB FOOT:
In horses, a flexural deformity of the coffin joint resulting in a raised heel; not to be confused with the club foot deformity of human beings.
COAGULATION:
Blood clotting.
COBALAMIN:
Cobalt-containing component of vitamin B12.
COCCIDIOIDOMYCOSIS:
The main systemic fungal infection of importance in horses in the United States, characterized by chronic weight loss, persistent coughing, musculoskeletal and/or abdominal pain, intermittent fever, and superficial abscesses; caused by Coccidioides immitis.
COCHLEA:
Curled bone in the inner ear which contains the organ of Corti, the actual organ of hearing.
CODOMINANT ALLELES:
Genes wherein both members of an allelic pair are fully expressed.
COFFIN BONE:
The distal phalanx or toe of the forelimb, incorporated within the hoof.
COGGINS TEST:
Test for detection of antibody to equine infectious anemia (EIA) virus.
COITUS:
Sexual intercourse.
COLIC:
Acute abdominal pain.
COLITIS:
Inflammation of the large bowel (colon); contrasts with enteritis (inflammation of the small intestine).
COLLAGEN:
Protein constituent of connective tissue.
COLOBOMA:
A defect of any tissue of the eye.
COLON:
The portion of the large intestine connecting the cecum (lowermost portion of the small intestine) with the rectum.
COLONOSCOPY:
Endoscopic examination of the colon.
COLOR FLOW DOPPLER ECHOCARDIOGRAPHY:
Technique using sound waves to examine the direction and velocity of blood flow within the heart and great vessels, allowing the cardiologist to observe directly the regions of abnormal blood flow that develop in association with most common cardiac abnormalities.
COLOSTRUM (“FIRST MILK”):
Milk produced by the mare during the first day or two after the birth of her foal; it is high in protein and protective antibodies (maternal immunity).
COMA:
Unconsciousness from which one cannot be aroused.
COMATOSE:
Unconscious and unable to be aroused.
COMMINUTED FRACTURE:
Fracture in which the affected bone is broken or crushed into small fragments.
COMMISSURE OF THE LIPS:
The corner of the mouth.
COMPLEMENT SYSTEM:
A specialized series of blood proteins whose major role is to disrupt the surface structure of microbes and altered body cells, resulting in their destruction.
COMPLETE BLOOD COUNT (CBC):
Blood analysis containing an enumeration of the number of red and white blood cells per unit of blood volume, the proportions of the different white blood cell types, and the amount of hemoglobin present.
COMPOUND FRACTURE:
Fracture that breaks through the skin; open fracture.
COMPUTERIZED AXIAL TOMOGRAPHY (CAT SCAN):
Highly specialized diagnostic X-ray technique that produces cross-sectional images of the inside of the body.
CONCENTRATES:
Rich sources of individual nutrients that are used to enhance the quality of the diet.
CONCEPTUS:
Embryo or fetus plus the accompanying extraembryonic membranes.
CONCUSSION:
A violent blow to the head, usually resulting in the loss of consciousness.
CONES:
Photoreceptor cells in the retina of the eye that are responsible for color vision and visual acuity.
CONFORMATION:
The overall physical appearance of a horse, reflecting the arrangement of muscle, bone, and other body tissues.
CONGENITAL:
Present at birth.
CONGENITAL HYPOTRICHOSIS:
Hairlessness.
CONGENITAL STATIONARY NIGHT BLINDNESS:
An hereditary abnormality of vision affecting Appaloosas.
CONGENITAL TESTICULAR HYPOPLASIA:
Underdevelopment of the testicles.
CONGESTIVE HEART FAILURE:
Syndrome caused by the inadequate pumping of blood by the heart.
CONIDIOBOLOMYCOSIS:
A form of phycomycosis caused by Conidiobolus coronatus, characterized by a thick nasal discharge, coughing, respiratory difficulty, and halitosis (bad breath).
CONJUNCTIVA:
Mucous membrane lining the eyelids and covering the white surface (sclera) of the eyball.
CONJUNCTIVITIS:
Inflammation of the conjunctiva.
CONNECTIVE TISSUE:
A general term encompassing the different types of supportive tissues that hold together many body structures.
CONSTITUTIONAL SIGNS:
Generalized clinical signs, such as inappetence, lethargy, weight loss.
CONTAGIOUS EQUINE METRITIS:
Highly contagious disease characterized by inflammation of the female genital tract and production of a thin, profuse, grayish-white discharge from the vulva; caused by a bacterium, Taylorella equigenitallium.
CONTINUOUS HEART MURMUR:
A murmur that is present during both contraction and relaxation of heart muscle.
CONTRACTED TENDONS:
A developmental orthopedic disease of foals, associated with rapid growth rates and high planes of nutrition.
CONTRALATERAL:
On the opposite side.
CONTUSION:
A bruise.
CONVULSIONS:
Seizures.
COOMBS’ TEST:
An immunologic procedure for the detection of autoantibody attached to red blood cells; also called an antiglobulin test; important in disease diagnosis as well as in cross-matching blood samples for transfusion purposes.
COPROPHAGY:
The eating of feces.
COR PULMONALE:
Disease of the right side of the heart caused by increased pressure within the pulmonary artery.
CORACIDIUM:
Free-swimming larval form of pseudophyllidean tapeworms.
CORE BIOPSY:
Biopsy obtained from an awake patient using local anesthesia and a specialized small-bore biopsy needle.
CORNEA:
The transparent outer coat of the eye.
CORNIFIED:
Converted into hardened tissue; keratinized.
CORNS:
Chronic lesions found in the sole of the foot, at the angle formed by the wall and the bar of the sole.
CORNSTALK DISEASE:
Common name for leukoencephalomalacia.
CORONARY BAND:
Ring of vascular tissue along the upper edge of the hoof wall from which the horn of the hoof grows.
CORONITIS:
Inflammation of the coronary band.
CORPORA NIGRA:
A row of dark protuberances normally present along the upper border of the equine iris; also called granula iridica.
CORPUS LUTEUM (PLURAL: CORPORA LUTEA):
Ovarian follicle after discharge of the ovum (egg); it secretes the hormone progesterone.
CORTEX:
Outer layer of an organ (kidney, adrenal gland, brain) or hair shaft; contrasted with medulla.
CORTICOSTEROIDS:
Steroid hormones (cortisol, corticosterone, etc.) produced by the cortex of the adrenal gland
CORTICOSTERONE:
A corticosteroid hormone.
CORTISOL:
A corticosteroid hormone.
CORTISONE:
A corticosteroid hormone (a precursor of cortisol) found in small quantities in the adrenal cortex.
CRANIAL:
Toward the head; pertaining to the head.
CRANIAL NERVES:
Nerves originating largely in the brain stem that control the facial muscles and certain specialized activities of the head (sight, smell, hearing).
CREATINE KINASE (CK):
A muscle-specific enzyme found in serum; determination of CK levels represents a useful tool for the diagnosis of muscle disorders.
CREATININE:
Nitrogen-containing compound generated from the breakdown of ingested proteins.
CREEP FEED:
Feed provided in a separate area where the foal can eat without interference from the mare.
CREMASTER MUSCLE:
Muscle that suspends the testicle.
CRIBBING:
A stable vice in which the horse places its upper teeth on the edge of a feeder or fence, arches its neck, inhales, and often produces a grunt or belching sound.
CROSS-MATCH:
Procedure by which blood samples from donor and recipient are tested before blood transfusion, in order to determine compatibility.
CROSS-TIES:
Fixed lines attached to each side of the halter.
CROUP:
Hindquarters; area between the hips and the point of the buttocks.
CROWN:
The portion of a tooth that lies above the gum line.
CRYOGEN:
Any substance, such as liquid nitrogen, used to produce extreme cold during cryosurgery.
CRYOSURGERY:
A procedure by which local application of intense cold (freezing) is used to destroy unwanted tissue.
CRYPTORCHIDISM:
Developmental defect wherein one or both of the testicles has not descended into the scrotum.
CRYPTOSPORIDIOSIS:
Diarrheal disease of debilitated or immunodeficient foals, caused by a protozoan, Cryptosporidium parvum.
CULICOIDES HYPERSENSITIVITY:
Allergic skin disease caused by the bites of midges of the genus Culicoides; also known as Queensland itch and sweet itch.
CUNEAN BURSITIS:
Inflammation of the cunean bursa underneath the cunean tendon, which travels over the front and inside of the hock.
CURB:
Inflammation and thickening of the plantar ligament (the ligament that courses along the back of the calcaneus bone in the hock).
CUSHING’S DISEASE:
Hyperactivity of the adrenal cortex, representing the most common endocrine disorder of horses.
CUSPS:
The sharp points of the tooth crown.
CUTANEOUS:
Pertaining to the skin.
CUTANEOUS HABRONEMIASIS:
A skin disease of horses caused by stomach worms (Habronema spp.); also called summer sores.
CUTANEOUS HORNS:
Projections of hardened skin.
CUTANEOUS ONCHOCERCIASIS:
Skin disease caused by Onchocerca cervicalis, a threadworm that lives in the nuchal ligament of the neck.
CUTICLE:
The outermost layer of a hair shaft; also, the thick, noncellular covering on the surface of a roundworm (nematode) parasite.
CYANOCOBALAMIN:
Vitamin B12.
CYANOSIS:
A bluish discoloration of the skin and mucous membranes, resulting ultimately from a deficiency of oxygen in the blood.
CYST:
Simple, saclike cavity that can develop in any of a number of different body tissues; it usually contains fluid or a semisolid, cheesy or doughy material.
CYSTADENOMA:
A benign tumor of cystic and glandular structures.
CYSTITIS:
Inflammation of the urinary bladder, often occurring secondary to diseases causing incomplete emptying of the bladder.
CYTOKINES:
“Messenger molecules” by which cells of the immune system signal and instruct one another; the interferons and the interleukins are examples.
CYTOLOGIC EXAMINATION, CYTOLOGY:
The microscopic examination of cells obtained by scraping, aspiration, or biopsy, for the purpose of disease diagnosis.
CYTOPLASM:
Cell protoplasm; the fluid and particulates within a cell, exclusive of the cell nucleus.
CYTOTOXIC:
Harmful to cells.
DECIDUOUS TEETH:
“Milk teeth,” the temporary teeth that are lost to make way for the permanent teeth.
DEFINITIVE HOST:
Host in or on which a parasite reaches sexual maturity or undergoes sexual reproduction.
DEGENERATIVE JOINT DISEASE:
Term for a group of disorders resulting in progressive deterioration of the articular cartilage of a joint, accompanied by bone proliferation around the joint margins and thickening of the soft tissues of the joint; also called degenerative arthritis.
DEGRANULATION:
Release of granules from a cell.
DEHISCENCE:
Breakdown of healing at a wound or suture site.
DEHYDRATION:
Loss of body water, occurring when the intake of water is insufficient to cover water losses.
DEMARCATED:
Having sharp borders.
DEMATIACEOUS FUNGI:
Dark, pigmented fungi represented by the genera Drechslera, Alternaria, and others.
DEMENTIA:
Mental deterioration.
DENDRITES:
Short threadlike extensions of a nerve cell; they act to receive nerve impulses from adjacent nerve cells.
DENSITY:
The concentration of a nutrient in a feed.
DENTAL FLOAT:
Veterinary instrument for grinding down enamel points.
DENTIN:
The tooth layer lying between the inner pulp (containing the tooth’s blood and nerve supply) and the overlying enamel.
DEOXYGENATED:
Having a low oxygen content; said of venous blood.
DEOXYRIBONUCLEIC ACID (DNA):
The genetic material of living cellular organisms and of certain viruses.
DEPIGMENTATION:
Localized loss of normal skin color.
DEPOLARIZATION:
A change from a negative to a positive charge, generating an electrical wave (as in the production of the heartbeat).
DERMAL PAPILLA:
Structure at the base of each hair follicle that, with the associated hair matrix cells, is responsible for the production of hair.
DERMATITIS:
Any inflammatory skin disease.
DERMATOMYCOSIS:
Any fungal skin infection.
DERMATOPHILOSIS:
Relatively sporadic skin disease caused by an unusual threadlike bacterium, Dermatophilus congolensis; also known as streptothricosis and rain-scald.
DERMATOPHYTES:
Fungi causing ringworm.
DERMATOPHYTOSIS:
Ringworm.
DERMATOSIS:
Any skin disease, particularly one without an inflammatory component.
DERMIS:
The middle and thickest major layer of the skin; composed of connective tissue fibers and a ground substance, it lies just beneath the epidermis, the outermost layer of the skin.
DERMOID:
A misplaced piece of skin found on the conjunctiva as a congenital lesion; it may also involve the cornea.
DESMITIS:
Inflammation of a ligament.
DETOXIFICATION:
Reduction in toxic properties of compounds.
DETRUSOR:
Smooth muscle layer of the bladder wall; contraction of the detrusor results in voiding of urine.
DEXTROSE:
Glucose; blood sugar.
DIABETES MELLITUS:
Diabetes, a chronic disease caused by either insufficient production of insulin by the islets of Langerhans in the pancreas, or by resistance of target tissues to the effects of insulin. Diabetes results in an inability of cells to utilize glucose (blood sugar), with widespread adverse effects owing to impaired utilization of carbohydrates, fats, and proteins by the body.
DIABETIC KETOACIDOSIS:
Serious, life-threatening complication of untreated or poorly treated diabetes mellitus, characterized by the buildup of ketone bodies in the circulation and a fall in blood pH, i.e., increasing acidity of the blood.
DIAPHRAGM:
The large muscle used for breathing which separates the abdominal and chest cavities.
DIAPHRAGMATIC HERNIA:
Rupture of the diaphragm, with movement of some of the abdominal contents into the chest cavity.
DIAPHYSIS:
The central shaft of a long bone.
DIARRHEA:
An increase in the fluid content, volume, or frequency of bowel movements.
DIASTOLE:
The relaxation/filling phase of the heartbeat, following systole.
DIASTOLIC BLOOD PRESSURE:
The pressure that occurs when the heart is not pumping blood into the arterial system (i.e., during the relaxation period between contractions).
DIASTOLIC HEART MURMUR:
Murmur that is present only during diastole (the relaxation phase of the heartbeat).
DIESTRUS:
The quiescent period between one estrus period and the next; also called interestrus.
DIFFERENTIAL WHITE BLOOD CELL COUNT:
Total white blood cell (WBC) counts and percentages of different WBC types present; component part of a complete blood count (CBC).
DIFFERENTIATION:
The development of cellular specialization as cells mature.
DIGESTIBLE CARBOHYDRATES:
Sugars and starches.
DIGESTIBLE ENERGY (DE):
For a feed, the sum of the digestible carbohydrate, protein, fat, and fiber; also called total digestible nutrients (TDN).
DIGESTION:
The breakdown of larger substances into smaller subunits, which can be more readily carried into the body for use in energy production and the construction of body tissues.
DIGITAL PRESSURE:
Pressure applied by the fingers.
DIGITAL PULSE:
The pulse as felt in the digital arteries of the feet; important for the detection of laminitis (founder).
DIGOXIN:
Medication that increases the strength of the heartbeat while decreasing the heart rate; used most often for the treatment of congestive heart failure.
DILATED:
Enlarged or widened; expanded.
DILATED FIXED PUPIL:
Pupil that does not contract.
DILATION:
Expansion.
DIRECT LIFE CYCLE:
With regard to parasites, a life cycle that can be completed without the participation of an intermediate host.
DISCOSPONDYLITIS:
Inflammation of an intervertebral disk.
DISPENSABLE AMINO ACIDS:
Amino acids that can be synthesized by the body so long as a source of nitrogen is present in the diet.
DISSEMINATED INTRAVASCULAR COAGULATION (DIC):
A bleeding disorder characterized by the excessive utilization of blood-clotting factors, due to widespread clotting within blood vessels; the resultant hemorrhaging often represents a terminal event in a number of diseases.
DISTAL:
Farther, more distant.
DISTEMPER:
Alternative name for strangles.
DISUSE ATROPHY:
Loss of muscle mass because of muscle disuse.
DIURETIC:
Any drug that promotes urination.
DIURNAL:
Having a daily cycle or rhythm.
DNA:
Deoxyribonucleic acid, the genetic material of living cellular organisms and of certain viruses.
DOMINANT GENE:
A gene capable of expressing its trait even when carried by only one member of a chromosome pair.
DOPPLER ECHOCARDIOGRAPHY:
Technique using sound waves to examine the direction and velocity of blood flow within the heart and great vessels.
DORSAL:
Pertaining to the back; toward the back.
DUCT:
Tiny tube or passageway.
DUCTUS ARTERIOSUS:
Blood vessel normally present during fetal life that allows blood to bypass the lungs, which of course are nonfunctional at this time; the ductus normally closes shortly after birth.
DUODENUM:
The first part of the small intestine, connecting the stomach with the jejunum.
DYSGERMINOMA:
Malignant but extremely rare tumor of the ovary.
DYSPHAGIA:
Difficult or painful swallowing.
DYSPLASIA:
Any abnormality in the size, shape, or development of cells.
DYSPNEA:
Difficulty breathing; labored breathing.
DYSTOCIA:
Difficult birth.
DYSURIA:
Painful or difficult urination.
ECCRINE SWEAT GLANDS:
Sweat glands that empty their contents directly onto the skin surface
ECHINOCOCCOSIS:
Hydatid disease
ECHOCARDIOGRAPHY:
Examination of the heart by means of ultrasonic sound waves, for the purpose of disease diagnosis; also known as cardiac ultrasound
ECLAMPSIA:
Calcium deficiency in a lactating mare
ECTOPARASITE:
External parasite; examples include ticks, fleas, and mites
ECTOPIC:
In or at an abnormal site; not in the normal position
EDEMA:
The accumulation of abnormally large quantities of fluid in the intercellular tissue spaces (spaces between cells); pulmonary edema refers specifically to fluid buildup in the lungs
EDEMATOUS:
Swollen with fluid
EFFUSION:
Fluid escaping into a body cavity or tissue
ELASTIN:
Protein found in elastic connective tissue fibers that imparts flexibility to the tissue
ELECTIVE SURGERY:
Surgery that is medically necessary but need not be performed immediately
ELECTROCARDIOGRAM (ECG):
Examination of the electrical activity of the heart, for the purpose of disease diagnosis. The ECG records the size and direction of the waves of depolarization that spread across the heart during muscle contraction and relaxation
ELECTROENCEPHALOGRAPHY (EEG):
Examination of the electrical activity of the brain, for the purpose of disease diagnosis
ELECTROLYTES:
Simple, inorganic salts that act as charged particles in water solutions, i.e., they are able to conduct electricity; examples include sodium, potassium, and chloride
ELECTROMYOGRAPHY (EMG):
Examination of the electrical activity within a muscle at rest or during voluntary or evoked muscular contractions, for the purpose of disease diagnosis
ELECTROPHORESIS:
Separation of components of a mixture by their differing migration in an applied electric field
ELECTRORETINOGRAM (ERG):
Examination of the electrical activity of the retina (light-sensitive layer of cells at the back of the eye), for the purpose of disease diagnosis
ELECTROSURGERY:
Surgical techniques (such as electrocautery) wherein electrical methods are used to remove tissue and/or seal broken blood vessels to alleviate hemorrhage
ELISA:
Enzyme-linked immunosorbent assay; any of the many highly sensitive color-based test methods for detecting either antibody or antigen in blood, serum, or plasma
EMBOLISM:
Sudden blockage of an artery by a blood clot
EMBRYONIC VESICLE:
The fertilized egg (embryo) with its surrounding fluid and membranes
EMETICS:
Drugs used to induce vomiting
ENAMEL:
The thin, calcium-rich outer surface of the teeth, overlying the harder dentin layer; it functions to resist wear
ENAMEL HYPOPLASIA:
Underdevelopment or incomplete development of the enamel layer of a tooth
ENAMEL POINTS:
Sharp points that develop in the enamel of the teeth, owing to the normal positioning and growth of the teeth in the mouth; the sharp points can be ground down with a special instrument called a dental float
ENDOCARDITIS:
Inflammation of the innermost lining of the heart (endocardium), usually caused by bacterial infection of one or more heart valves
ENDOCARDIUM:
A thin serous membrane, the innermost lining of the chambers of the heart
ENDOCRINE GLANDS:
Glands that secrete their contents directly into the blood or interstitial fluid (the fluid surrounding cells)
ENDOCRINOLOGY:
The study of hormones and hormone-producing glands
ENDOCRINOPATHY:
Hormonal imbalance leading to disease
ENDOGENOUS:
Originating within the body
ENDOMETRITIS:
Inflammation of the innermost lining of the uterus; the leading cause of infertility in broodmares
ENDOPARASITE:
Any parasite found inside the host, chiefly in the gastrointestinal tract
ENDOSCOPY:
Procedure wherein tubelike viewing apparatus (an endoscope) is inserted into an orifice or body cavity, for the purpose of examining the internal portions of that cavity or a hollow organ
ENDOSPORE:
The type of spore produced during the spherule stage of the life cycle of the fungus Coccidioides immitis, the cause of coccidioidomycosis ("valley fever")
ENDOTRACHEAL TUBE:
A plastic tube for breathing, commonly inserted into the trachea during general anesthesia
ENERGY DENSITY:
The amount of energy contained in a given quantity of food
ENOPHTHALMOS:
Recession of the eye deep within the orbit
ENTERIC:
Referring to the small intestine
ENTERITIS:
Inflammation of the small intestine; contrasts with colitis (inflammation of the large intestine)
ENTEROLITH:
Stony concretion that develops in the large intestine
ENTROPION:
Turning in of an eyelid
ENUCLEATION:
Surgical removal of the eyeball
ENZOOTIC:
Widespread in a population and always present, but producing disease in only relatively few animals; said of infectious disease agents
ENZYME:
Any of a myriad number of different proteins produced by cells, capable of accelerating biochemical reactions occurring within the cells
EOSINOPHIL:
A white blood cell that contains granules readily stained with eosin; functions in the allergic reaction to parasitic infections
EPICARDIUM:
The outermost membrane of the surface of the heart
EPIDERMAL APPENDAGES:
Collectively the hair follicles, sweat glands, and sebaceous glands
EPIDERMIS:
The outermost layer of the skin
EPIDERMOID CYST:
Follicular cyst
EPIDIDYMIS:
In the male, the duct connecting the testis to the vas deferens; used for the storage, maturation, and movement of sperm
EPILATION:
Plucking of hair by the roots
EPILEPSY:
Brain disorder resulting in seizures
EPINEPHRINE (ADRENALINE):
A hormone secreted by the adrenal glands; it acts to increase blood sugar levels and blood pressure and to accelerate the heart rate
EPIPHYSIS:
Either end of a long bone
EPISIOTOMY:
Surgical enlargement of the vulvar opening
EPISTAXIS:
Bleeding from the nostril; nosebleed
EPITHELIOGENESIS IMPERFECTA:
A rare, lethal skin defect of draft-horse foals; inherited as an autosomal recessive disorder
EPITHELIUM:
Cellular covering of the internal and external surfaces of the body
EPIZOOTIC:
Attacking many animals over a short period of time, with resulting high morbidity (high percentage of animals becoming ill); said of infectious disease agents. Also, an acute disease outbreak
EQUIDS:
Members of the horse family
EQUINE COITAL EXANTHEMA:
Disease characterized by painful wartlike lesions on the skin of the vulva and perineum or on the shaft of the penis; caused by equine herpesvirus type 3
EQUINE COLLAGENOLYTIC GRANULOMA:
The most common nodular skin disease of horses, possibly caused by a hypersensitivity to insect bites; also called nodular necrobiosis
EQUINE DEGENERATIVE MYELOENCEPHALOPATHY:
Chronic, progressive disease of young horses, characterized by abnormalities of gait; the cause is thought to be related to a vitamin E deficiency and is associated with lack of green forage or the feeding of heat-processed pelleted rations
EQUINE GRANULOCYTIC EHRLICHIOSIS:
Tick-transmitted disease characterized by fever, depression, reluctance to move, depressed white blood cell and platelet counts, and lower-limb swelling; caused by a rickettsia, Ehrlichia equi
EQUINE HERPESVIRUS MYELOENCEPHALITIS:
Inflammatory disorder of the brain and spinal cord, caused by
EQUINE HERPESVIRUS TYPE 1, THE ABORTION-INDUCING S:
EQUINE INFECTIOUS ANEMIA (EIA):
One of the most important viral diseases of horses, caused by a retrovirus; it is a chronic infection resulting in a persistent (lifelong) carrier state with periodic exacerbations of anemic illness; also called swamp fever
EQUINE INFLUENZA:
Very important viral respiratory disease of horses caused by subtypes (A1 and A2) of equine influenza virus, an orthomyxovirus
EQUINE MONOCYTIC EHRLICHIOSIS:
Potomac horse fever
EQUINE PROTOZOAL MYELOENCEPHALITIS:
Inflammatory disorder of the brain and spinal cord, caused by a poorly characterized protozoan parasite tentatively designated Sarcocystis neurona
EQUINE VIRAL ARTERITIS (EVA):
Contagious viral disease of horses causing fever, ocular and respiratory signs, fluid distension or swelling of the limbs, and abortion
EQUINE VIRAL ENCEPHALOMYELITIS:
Inflammation of the brain and spinal cord, caused by eastern equine encephalo-myelitis (EEE) virus, western equine encephalomyelitis (WEE) virus, or venezuelan equine encephalomyelitis (vee) virus
EQUINE VIRAL PAPILLOMATOSIS:
Disease characterized by the development of papillomas (warts) on the muzzle, around the lips, or on the extremities; caused by equine papillomavirus, a member of the Papovaviridae family of DNA viruses
ERECTILE TISSUE:
Tissue capable of erection, i.e., stiffening following engorgement of blood; found in the penis of the male and the clitoris of the female
EROSION:
A superficial denudation of the skin involving only the epidermis
ERUCTATION:
Forceful, retrograde expulsion of air from the stomach; "burping" or "belching."
ERYTHEMA:
Reddening of the skin, due to congestion of the underlying capillaries
ERYTHEMA CHRONICUM MIGRANS:
A skin reaction seen in human beings with Lyme borreliosis
ERYTHEMA MULTIFORME, EPIDERMAL TYPE:
An uncommon but highly characteristic skin disease with a proposed immunologic basis
ERYTHROCYTE:
Red blood cell, the carrier of oxygen in the blood
ERYTHROPOIETIN:
A hormone produced by the kidneys that stimulates red blood cell production in the bone marrow
ESOPHAGITIS:
Inflammation of the esophagus
ESOPHAGUS:
The muscular tube extending from the pharynx (back of the mouth) to the stomach
ESSENTIAL AMINO ACIDS:
Amino acids that cannot be synthesized in sufficient quantities by the body and therefore must be provided in the diet
ESSENTIAL FATTY ACIDS:
Fatty acids that have structural functions in cell membranes and serve as precursors for prostaglandins
ESTROGENS:
General term for female sex hormones
ESTRUS:
"Heat"; a recurrent period of varying length, during which the mare produces a watery secretion from the genital tract, becomes sexually receptive to the stallion, and ovulates
ETIOLOGY:
The cause of a disease
EUMYCOTIC MYCETOMA:
A swollen, progressing, tumorlike lesion caused by certain species of fungi
EUSTACHIAN TUBE:
Short canal that connects the middle ear with the back of the throat
EUTHANASIA:
Humane killing; putting to sleep
EXCISE:
To cut out; remove surgically
EXCISIONAL BIOPSY:
Biopsy sample representing an entire (small) lesion, removed surgically both as diagnosis and treatment
EXERTIONAL MYOPATHIES:
Muscle diseases caused by exertion; these include azoturia, tying-up, and endurance-related myopathy
EXHAUSTIVE DISEASE SYNDROME:
Condition seen in endurance horses, three-day event horses, and horses on long trail rides; characterized by a significant level of dehydration, owing both to massive losses of fluid and electrolytes in sweat and to decreased fluid intake
EXOCRINE GLANDS:
Glands that secrete their contents through ducts (tiny tubes)
EXOGENOUS:
Originating outside the body
EXOSTOSIS:
A benign growth protruding from the surface of a bone
EXPIRATION:
The act of breathing air out; exhalation
EXTENDER:
Fluid added to collected semen to increase or "extend" the volume
EXTERNAL URETHRAL SPHINCTER:
Sphincter located at the junction of the bladder and urethra
EXTRAGONADAL:
External to the testes
EXTRAOCULAR:
External to the eyeball
EXUDATE:
A high-protein fluid derived from blood and deposited in tissues or on tissue surfaces, usually as a result of inflammation.</p>
FABELLA (PLURAL: FABELLAE):
Small sesamoid bone occasionally found in the area of the knee.
FACULTATIVE PARASITE:
A parasite whose life cycle can be completed without a parasitic phase, but which may optionally include a parasitic phase under certain circumstances.
FALLOPIAN TUBES:
Uterine tubes or oviducts.
FAMILIAL:
Running in a family line; occurring in a family line with greater frequency than by chance alone.
FARCY:
A form of glanders that affects the skin; characterized by nodules, ulcers, and swollen lymph nodes and lymphatic channels, most often involving the legs or abdomen.
FASCIAE (SINGULAR: FASCIA):
Sheets of fibrous tissue that ensheath the muscles and define their shape.
FASCICULATIONS:
Frequent small, localized muscle contractions.
FAT-SOLUBLE VITAMINS:
Vitamins A, D, E, and K.
FEBRILE:
Having a fever.
FECAL FLOTATION:
Laboratory procedure for identification of parasite eggs in a fecal specimen.
FEMINIZATION:
Development of certain female sex characteristics in a male.
FEMUR:
Thigh bone.
FERAL:
Wild; untamed.
FERMENTABLE:
Able to be digested by intestinal microorganisms.
FETAL RESORPTION:
Disintegration of the fetus while in the uterus.
FETLOCK JOINT:
The joint between the long pastern bone and the cannon bone.
FEVER:
A rise in body temperature caused by a change in the thermoregulatory set-point in the brain; usually caused by disease.
FIBRIN:
An insoluble protein that forms the nucleus of a blood clot.
FIBRINOGEN:
Clotting factor in the blood, is converted into its active form (fibrin) by the enzyme thrombin.
FIBROBLAST:
Immature fibrocyte.
FIBROSARCOMA:
A malignant tumor of connective tissue cells.
FIBROSIS:
Formation of fibrous tissue; scarring.
FIBROUS TISSUE:
Tough connective tissue.
FIBROUS TUNIC:
The outer layer of the eyeball.
FILAMENTOUS:
Threadlike.
FLAGGING:
Rhythmic up-and-down movements of the stallion’s tail during ejaculation.
FLATULENCE:
Presence of excessive air or gas within the intestinal tract.
FLEHMEN REACTION:
A unique behavior wherein the horse extends its head and curls back the upper lip while drawing air into the nasal cavity; usually expressed by a stallion attempting to detect estrus (“heat”) in a mare.
FLORA:
The population of microorganisms (bacteria, viruses, fungi, protozoa) normally resident within an individual host, or within a certain portion of the host (e.g., the intestinal tract).
FLUORESCEIN:
A fluorane dye used for, among other things, identifying ulcers on the cornea.
FOAL HEAT:
A mare’s first heat period after the birth of a foal.
FOAL HEAT SCOURS:
A normal physiological diarrhea occurring during the first heat cycle of a mare after foaling.
FOCAL VENTRAL MIDLINE DERMATITIS:
A frequently encountered skin disease of horses kept in close proximity to cattle; probably caused by the bites of horn flies.
FOLLICLE-STIMULATING HORMONE (FSH):
Hormone produced by the pituitary gland, that stimulates the development of ovarian follicles in the female and sperm production in the male.
FOLLICULAR CYST:
Cyst originating within a hair follicle; also called epidermoid cyst.
FOLLICULAR PHARYNGITIS:
Alternative name for chronic pharyngeal lymphoid hyperplasia.
FOLLICULAR SHEATH:
Long tubelike structure through which a hair passes through the dermis (middle layer of the skin) and exits to the skin surface.
FOLLICULITIS:
Inflammation of one or more hair follicles.
FORAGE DISEASE:
Common name for leukoencephalomalacia.
FORAGE POISONING:
Form of botulism in horses caused by ingestion of botulinal toxin produced by Clostridium botulinum in decaying plant material.
FOUNDER:
Common name for laminitis.
FROG:
Thickened, horny area located in the middle of the sole of the foot.
FROZEN-SECTION BIOPSY:
Biopsy sample frozen and cut for immediate examination and diagnosis, as during exploratory surgery.
FULMINANT:
Sudden and intense.
FUNDUS:
General term for the back of the eye.
FUNGAL TUMOR:
Eumycotic mycetoma.
FUNGI (SINGULAR: FUNGUS):
A large group of organisms characterized by the presence of a rigid cell wall and the absence of chlorophyll, and whose primary purpose is the decomposition of organic material; examples include the yeasts and molds, mushrooms, smuts, and rusts.
GALVAYNE’S GROOVE:
A dark line that forms on the outside of the corner incisor teeth; its length and appearance are useful in aging a horse.
GAMETES:
Reproductive cells, each containing a single set of chromosomes; ova (eggs) in the female and spermatozoa (sperm) in the male.
GAMETOGAMY:
Sexual reproduction involving the formation of male and female reproductive cells which fuse to form a zygote; also called syngamy.
GANGRENE:
Death and decay of tissue, usually owing to the loss of blood supply and subsequent invasion by bacteria.
GAS COLIC:
Colic caused by overconsumption of lush grass feed, resulting in excessive gas production in the intestine.
GASKIN:
The portion of the hind limb below the stifle.
GASTRIC:
Pertaining to the stomach.
GASTRITIS:
Inflammation of the stomach.
GASTROESOPHAGEAL SPHINCTER:
Sphincter located between the esophagus and the stomach.
GASTROSCOPY:
Endoscopic examination of the stomach.
GASTRULA:
An early stage of the developing embryo that follows the blastula stage.
GAUGE:
A measure of the diameter of an injection needle.
GELDING:
Castrated male horse.
GENE LINKAGE:
Phenomenon wherein genes located on the same chromosome tend to be inherited together more often than they are split apart.
GENERA:
Plural form of genus.
GENES:
The individual units of inheritance, composed of stretches of DNA found along the chromosomes within the nucleus of every cell.
GENOME:
The total genetic information of an individual cell or virus.
GENOTYPE:
The genetic makeup of a given physical trait; also, the total genetic makeup of an individual organism.
GENUS (PLURAL: GENERA):
One of the major classifying categories of taxonomy, further divided into species or subgenera.
GERIATRICS:
Branch of medical science concerned with the diseases, disabilities, and care of aged patients.
GESTATION:
The full period of pregnancy, from fertilization of the egg by a spermatozoon until birth.
GIARDIASIS:
Chronic diarrhea caused by the protozoan Giardia.
GINGIVA:
The gums of the mouth.
GINGIVITIS:
Inflammation of the gums.
GLAND:
Collection of cells that produces secretions or excretions of a specialized character.
GLANDERS:
An ancient and once worldwide bacterial disease of equids, now rare and restricted to certain areas of the Middle East and Asia; caused by Pseudomonas mallei.
GLANS PENIS:
The cap-shaped termination of the penile shaft.
GLAUCOMA:
Group of diseases caused by increased pressure within the eyeball, which damages the optic nerve and can result in blindness.
GLOBE:
The eyeball.
GLOMERULAR FILTRATION RATE (GFR):
Rate at which the kidney glomeruli filter the blood passing through them.
GLOMERULONEPHRITIS:
An inflammatory disease involving the capillaries (small blood vessels) of the kidney glomeruli.
GLOMERULUS (PLURAL: GLOMERULI):
Any one of the many tiny clusters of blood vessels within the kidney; they filter waste products from the blood and excrete them in the form of urine, which is transported to the bladder for elimination.
GLUCOCORTICOIDS:
Steroid hormones such as cortisol that are produced by the cortex of the adrenal gland; they elevate blood sugar levels, increase fat and protein breakdown and the secretion of stomach acid, and exert an anti-inflammatory effect on conditions such as arthritis and dermatitis.
GLUCOSE:
Blood sugar, the body’s most important fuel molecule.
GLUCOSURIA:
Spillage of glucose into the urine, as in diabetes mellitus.
GLYCOGEN:
Animal starch; a complex carbohydrate stored primarily in the liver and muscles, and broken down into its component glucose (sugar) molecules whenever they are needed by the body.
GOITER:
An enlarged thyroid gland.
GOITROGEN:
Any substance that causes goiter.
GONADAL HYPOPLASIA:
Underdevelopment of the gonads (testes or ovaries).
GONADOTROPIN-RELEASING HORMONE (GNRH):
Hormone released from the hypothalamus of the brain, that triggers the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland.
GONADS:
Ovaries (in the mare) and testes (in the stallion); the reproductive glands that produce ova (eggs) in the female and spermatozoa (sperm) in the male, as well as the sex hormones progesterone and estrogen (ovaries), and testosterone (testes).
GOSSYPOL:
A toxic fatty acid that can be found in cottonseed meal.
GRAM STAIN:
A routine stain used for the laboratory identification of bacteria.
GRANULA IRIDICA:
Corpora nigra.
GRANULAR CELL LAYER:
A layer of cells within the epidermis, the outermost layer of the skin; it lies above the prickle cell layer and below the horny layer.
GRANULATION TISSUE:
Newly formed, velvety tissue, rich in blood vessels but lacking nerve endings, that develops at the site of a healing wound; “proud flesh.”
GRANULE:
A tiny grain or particle.
GRANULOCYTES:
White blood cells that contain stainable granules; examples include neutrophils, eosinophils, and basophils.
GRANULOCYTIC LEUKEMIA:
Cancer of granulocytes.
GRANULOMA:
Lesion indicative of a chronic inflammatory response, characterized by the accumulation of white blood cells around an offending agent for the purpose of walling off the agent from the rest of the body.
GRANULOSA CELLS:
The cells that surround the developing ovarian follicle.
GRAVEL:
Common term describing drainage at the coronary band of the foot; caused by infection that migrates up the hoof wall and breaks out as an abscess at the coronary band.
GREASE HEEL:
General term for a variety of inflammatory skin conditions affecting the pastern region.
GROSS APPEARANCE:
Appearance as viewed by the unaided (naked) eye; as opposed to microscopic appearance.
GROWTH HORMONE (GH):
Hormone produced by the pituitary gland; it controls the rate of body growth.
GUTTURAL POUCH:
In horses, an internal sac that represents an outgrowth of the eustachian tube, the short canal that connects the middle ear with the back of the throat and that acts to equalize pressure within the ear.
GUTTURAL POUCH EMPYEMA:
Accumulation of the pus in the guttural pouch, often a complication of strangles.
GUTTURAL POUCH MYCOSIS:
Fungal infection of the guttural pouch, usually caused by fungi of the genus Aspergillus.
GUTTURAL POUCH TYMPANY:
Distension of the guttural pouch.
GYMKHANA:
Athletic event.
HABITUATION:
Learning process wherein the response to a repeated stimulus gradually declines, resulting eventually in the total absence of the response; becoming desensitized.
HAIR BULB:
The deepest portion of the hair follicle; its cells are referred to as hair matrix cells.
HAIR FOLLICLE:
The structural unit of hair production within the skin, containing two major components, the follicular sheath and the hair bulb; two major types exist, simple follicles and compound follicles.
HAIR MATRIX CELLS:
Cells at the base of the hair follicles that together with the dermal papilla are responsible for the production of hair.
HAIR MATRIXOMA:
Benign skin tumor arising from cells at the base of hair follicles (hair matrix cells).
HAIR ROOT:
The lower, anchoring structure of a hair.
HAIR SHAFT:
The upper, free portion of a hair; as distinguished from the hair root.
HARD PALATE:
Bone and tissue composing the roof of the mouth, separating the nasal cavity from the oral cavity.
HEAD-NODDING:
A stable vice characterized by a repetitive bobbing motion of the head, usually performed alone in a stall while in a drowsy state of consciousness.
HEAD-SHAKING:
A normal behavior that developed as a defense mechanism against irritating and often biting insects.
HEART MURMUR:
An abnormal heart sound produced when blood flows too rapidly or too chaotically through a portion of the heart; a common sign of heart disease.
HEART RATE:
The heart’s rate of contraction (systole) and relaxation (diastole).
HEAVES:
Common term for chronic obstructive pulmonary disease.
HELMINTHOSIS:
Any parasitic worm infestation.
HELMINTHS:
Parasitic worms.
HELPER T CELLS:
T lymphocytes that have a major role in assisting other lymphocytes, known as B cells, to produce antibody against an antigen.
HEMAGGLUTININS:
Autoantibodies directed against the body’s own red blood cells.
HEMANGIOMA:
Benign tumor of newly formed blood vessels.
HEMANGIOSARCOMA:
Malignant tumor of blood vessels and associated tissue.
HEMARTHROSIS:
Bleeding into a joint.
HEMATINICS:
Compounds that improve the quality of the blood; “blood builders.”
HEMATOCRIT:
The percentage of red blood cells in a specified volume of whole blood; measurement of the hematocrit is performed to check for anemia; also called packed cell volume (PCV).
HEMATOLOGIC:
Referring to the blood and/or blood cells.
HEMATOPOIESIS:
The production of new red blood cells.
HEMATURIA:
Presence of blood in the urine.
HEMERALOPIA:
“Day blindness,” a disorder of the retina characterized by blindness during the day but partial return of vision in dim light.
HEMOGLOBIN:
An iron-containing pigment found in red blood cells; it serves as the carrier of oxygen to the tissues.
HEMOGLOBINURIA:
Presence of hemoglobin in the urine; “red water.”
HEMOGRAM:
Results of blood examination including red blood cell count, packed cell volume (PCV) or hematocrit, and total and differential white blood cell counts.
HEMOLYSIS:
Red blood cell destruction.
HEMOLYTIC:
Characterized by red blood cell destruction.
HEMOLYTIC DISEASE OF THE NEWBORN:
Neonatal isoerythrolysis.
HEMOPHILIA A:
Recessive, X-linked bleeding disorder characterized by a deficiency of clotting factor VIII; the most common bleeding disorder of horses.
HEMOPTYSIS:
Coughing up blood.
HEMORRHAGE:
Bleeding.
HEMORRHAGIC DIATHESIS:
Disease condition in which an abnormal bleeding tendency exists, as in disseminated intravascular coagulation (DIC).
HEMORRHAGIC ENTERITIS:
Inflammation of the intestine accompanied by bleeding in the intestinal tract.
HEMORRHAGIC SHOCK:
Shock caused by severe bleeding (usually from trauma) resulting in depletion of blood from the circulatory system, so that less oxygen is transported from the lungs to the tissues.
HEMOSPERMIA:
Blood in the semen.
HEMOTHORAX:
Pooling of blood in the chest cavity.
HEPARIN:
An anticoagulant; it prevents blood clotting by indirectly inhibiting the formation of fibrin (the chief protein component of blood clots).
HEPATIC:
Pertaining to the liver.
HEPATIC LIPIDOSIS:
Abnormal accumulation of fat in liver cells.
HEPATIC NECROSIS:
Liver-cell death.
HEPATOMEGALY:
Enlargement of the liver.
HEPATOPATHY:
Any disease of the liver, particularly one characterized by degenerative changes.
HEPATOSPLENOMEGALY:
Enlargement of the liver and spleen.
HEREDITARY MULTIPLE EXOSTOSIS:
Inherited bone disorder characterized by the development of numerous small projections along the bones, resulting in an abnormal bony contour.
HERMAPHRODITISM:
Presence of male and female sex organs in the same individual.
HERNIA:
Protrusion of an organ or tissue through an abnormal fissure; rupture.
HETEROZYGOUS:
Having inherited a different allele from each parent, at a given locus on a chromosome; contrasted with homozygous, in which the same allele for a given trait is inherited from both parents.
HIGH RINGBONE:
Ringbone affecting the pastern joint.
HINNY:
Animal produced by crossing a jennet (female donkey) with an equine stallion.
HISTAMINE:
Powerful molecule produced by mast cells and basophils, that is responsible for an army of unpleasant effects seen in allergy; it causes contraction of smooth muscle and dilation of capillaries and increases the heart rate, among other actions.
HISTIOCYTE:
A tissue macrophage.
HISTIOCYTOMA:
Benign skin tumor composed of histiocytes (tissue macrophages).
HISTOLOGY:
The microscopic examination of normal tissue.
HISTOPATHOLOGY:
The microscopic examination of diseased tissue.
HOBBLING:
Tieing the legs together.
HOCK JOINT:
Position in the hind limb where the tibia joins the tarsal bones; equivalent to the human ankle and heel.
HOLOCRINE SECRETION:
Type of secretion in a gland wherein each entire gland cell disintegrates, with the cell contents becoming the secretion.
HOMOGENEOUS:
Uniform.
HOMOZYGOUS:
Having inherited the same allele for a particular trait from both parents.
HORMONE:
Any molecule produced by an organ or tissue, usually in extremely small quantities, that has a specific regulatory effect on the activity of another organ or tissue.
HORNER’S SYNDROME:
A specific set of clinical signs,constriction of the pupils, protrusion of the third eyelid, drooping of the upper eyelid, sweating of the face and neck on the affected side,resulting from partial interruption of the nerve supply to the eyes and head.
HORNY LAYER:
A cell layer of the epidermis, the outermost layer of the skin; it is composed entirely of tightly adherent, dead keratinocytes containing abundant quantities of keratin.
HOST:
The living organism in or on which a parasite resides.
HUMAN CHORIONIC GONADOTROPIN (HCG):
Hormone produced by the placenta that can stimulate ovulation.
HUMORAL IMMUNE RESPONSE:
The mounting of an antibody response to an antigen by the immune system.
HYDATID DISEASE:
Disease of humans caused by the tapeworms Echinococcus granulosus and Echinococcus multilocularis; characterized by the production in the tissues of large, fluid-filled structures (hydatid cysts), in which the parasite undergoes a further process of maturation.
HYDROCEPHALUS:
Cerebrospinal fluid accumulation within the brain.
HYDROMETRA:
Accumulation of watery fluid within the uterus.
HYDROPHILIC:
Having the property of attracting or absorbing water molecules.
HYDROTHERAPY:
Use of water externally as a therapeutic measure.
HYGROMA:
Fluid-filled sac or cyst, most often caused by trauma.
HYMEN:
Membranous tissue partially or completely covering the external opening of the vagina in virgin mares.
HYPER-:
A prefix meaning above or beyond; excessive.
HYPERAMMONEMIA:
Abnormally elevated ammonia levels in the blood.
HYPERANDROGENISM:
Excessive production of male sex hormones.
HYPERCALCEMIA:
Abnormally elevated levels of calcium in the blood.
HYPERCHLOREMIA:
Abnormally elevated levels of chloride in the blood.
HYPERELASTOSIS CUTIS:
Skin disease of Quarter Horses, characterized by a lack of subcutaneous attachment of the skin to the underlying tissues.
HYPEREMIA:
Reddening caused by increased blood flow.
HYPERESTROGENISM:
Excessive production of the female sex hormone estrogen.
HYPERGLYCEMIA:
Abnormally elevated levels of glucose (blood sugar) in the blood.
HYPERHIDROSIS:
Excessive sweating.
HYPERKALEMIA:
Abnormally elevated levels of potassium in the blood.
HYPERKALEMIC PERIODIC PARALYSIS (HYPP):
Genetic disease of Quarter Horses and derived breeds (Paints, Appaloosas), characterized by sporadic episodes of generalized muscle tremors and stiffness accompanied by elevated serum levels of potassium.
HYPERKERATOSIS:
Abnormal overgrowth of the horny layer of the epidermis.
HYPERLIPIDEMIA:
Abnormally elevated levels of fat in the blood.
HYPERNATREMIA:
Abnormally elevated levels of sodium in the blood.
HYPERPARATHYROIDISM:
Hyperactivity of one or more parathyroid glands.
HYPERPHOSPHATEMIA:
Abnormally elevated levels of phosphorus in the bloodstream.
HYPERPIGMENTATION:
Localized, abnormal darkening of the normal skin color.
HYPERPLASIA:
Overgrowth due to an abnormal increase in the number of cells in a given tissue; contrasted with hypertrophy.
HYPERPROGESTINISM:
Excessive production of the hormone progesterone.
HYPERSENSITIVITY VASCULITIS:
An abnormal immunologic reaction targeted at blood-vessel walls.
HYPERTENSION:
Abnormally elevated blood pressure.
HYPERTHERMIA:
Abnormally elevated body temperature; also, a method of heating tumors to lethal temperatures in an attempt to kill tumor cells.
HYPERTHYROIDISM:
Abnormally increased activity of the thyroid gland, with elevated secretion of thyroid hormones; has not been reported to occur spontaneously in the horse.
HYPERTROPHY:
Overgrowth due to an abnormal increase in the size of cells in a given tissue; contrasted with hyperplasia.
HYPHEMA:
Bleeding into the anterior chamber of the eye.
HYPO-:
A prefix meaning below or under; deficient.
HYPOADRENOCORTICISM:
Addison’s disease; insufficient secretion of steroid hormones from the adrenal cortex.
HYPOALBUMINEMIA:
Abnormally low levels of the protein albumin in the blood, often reflecting abnormally low body stores of protein.
HYPOALLERGENIC:
Minimizing allergic reactions.
HYPOCALCEMIA:
Abnormally low levels of calcium in the blood.
HYPOCHLOREMIA:
Abnormally low levels of chloride in the blood.
HYPODERMIS:
Alternative name for subcutis.
HYPOGLYCEMIA:
Abnormally low levels of glucose (blood sugar) in the blood.
HYPOKALEMIA:
Abnormally low levels of potassium in the blood.
HYPOLUTEOIDISM:
Sterility in the female caused by insufficient secretion of the hormone progesterone.
HYPONATREMIA:
Abnormally low levels of sodium in the blood.
HYPOPARATHYROIDISM:
Insufficient secretion of parathyroid hormone (PTH) from the parathyroid glands.
HYPOPERFUSION:
Reduced blood flow.
HYPOPHOSPHATEMIA:
Abnormally low levels of phosphorus in the blood.
HYPOPLASIA:
Underdevelopment or incomplete development of a given tissue.
HYPOPROTEINEMIA:
Abnormally low level of plasma proteins in the blood.
HYPOPYON:
Accumulation of white blood cells (pus) in the anterior chamber of the eye.
HYPOSTATIC GENE:
A gene whose expression is masked by another gene.
HYPOTHALAMUS:
The part of the brain concerned with operation of much of the autonomic (unconscious) nervous system, the production of specific hormones that are subsequently stored in and released by the pituitary gland, and the regulation of body temperature, sleep cycles, and food and water intake.
HYPOTHERMIA:
Abnormally low body temperature; cooling of the body to slow metabolism.
HYPOTHYROIDISM:
Abnormally decreased thyroid function.
HYPOTRICHOSIS:
Condition characterized by a sparse hair coat.
HYPOVOLEMIA:
Abnormally decreased volume of circulating blood; can lead to shock.
HYPOXEMIA:
Abnormally low blood oxygen levels
HYPOXIA:
Oxygen deprivation.
IATROGENIC:
Arising as a complication of medical treatment.
IDIOPATHIC:
Having no known cause.
ILEOCECAL ORIFICE:
The point at which the small intestine joins the large intestine.
ILEUS:
Loss of normal intestinal motility.
IMMUNE COMPLEX:
Antibody attached to (complexed with) an antigen.
IMMUNE-MEDIATED, IMMUNOLOGICALLY MEDIATED:
Refers to any condition in which the deleterious effects are caused wholly or in part by components of the immune system.
IMMUNIZATION:
The administration of a vaccine in order to produce protective immunity against the infectious disease agent(s) present in the vaccine.
IMMUNOFLUORESCENCE ASSAY (IFA):
Assay technique for the detection of antigen or antibody using antibodies labeled with a fluorescent dye.
IMMUNOGLOBULINS (ANTIBODIES):
Specialized proteins produced by plasma cells (end-stage B lymphocytes) in response to the presence of foreign material (bacteria, viruses, toxins, etc.). Antibodies are capable of binding to the foreign material and thus alerting other immune cells to its presence. Often abbreviated Ig, there are five major classes: IgG, IgM, IgA, IgE, and IgD. In horses a subset of IgG known as IgG(T) is involved in the immune response to parasites and tetanus toxoid.
IMMUNOTHERAPY:
The use of medications that boost the immune response, to assist in the treatment of a disease.
IMPACTION COLIC:
Colic resulting in blockage of the intestine; can result from excessive consumption of grain or lush pasture, or ingestion of foreign material.
IN UTERO:
Within the uterus.
INACTIVATED (“KILLED”) VACCINE:
A vaccine in which the infectious agent has been modified in some way (most often chemically) so that it no longer can infect and replicate within the host, but nevertheless is still capable of stimulating an immune response.
INAPPETENCE:
Lack of appetite; anorexia.
INCISIONAL BIOPSY:
Biopsy sample representing a portion of a larger lesion.
INCISIONAL HERNIA:
A defect in a healing incision wound that results in a bulging out of the underlying tissues.
INCISORS:
The front teeth.
INCONTINENCE:
Loss of voluntary control over urination or defecation.
INCUBATION PERIOD:
The time between exposure to an infectious disease agent and the onset of clinical signs of disease.
INDIRECT LIFE CYCLE:
With regard to parasites, a life cycle that can only be completed with the participation of an intermediate host.
INFARCT:
Localized tissue death resulting from obstruction of the blood supply to the affected site.
INFECTIVE STAGE:
The specific stage in the life cycle of a parasite that is able to initiate an infection in a definitive or intermediate host.
INFERTILITY:
Diminished ability to produce offspring.
INFLAMMATION:
Protective response, often localized, involving white blood cells and other components of the body, wherein a disease agent or other irritant factor is sequestered and attempts made to destroy it or neutralize its effects.
INGESTA:
Ingested food.
INGUINAL:
Pertaining to the groin area.
INGUINAL CANAL, INGUINAL RING:
An opening deep within the groin area for passage of the spermatic cord or the round ligament of the uterus.
INHALATION PNEUMONIA:
Pneumonia caused by inhalation of noxious fumes, as during a house or forest fire.
INNERVATION:
The distribution of nerves to a particular tissue or body part.
INSOLUBLE FIBERS:
Dietary fibers such as cellulose and wheat bran; they are good bulk-forming agents and are only poorly fermented (digested) by bacteria in the large intestine.
INSPIRATION:
The act of breathing air in; inhalation.
INSULIN:
Critically important hormone produced by the beta cells of the endocrine pancreas; responsible for regulating the blood concentration of glucose, the body’s most important fuel molecule.
INSULIN-DEPENDENT DIABETES MELLITUS:
Diabetes mellitus characterized by an inability to utilize blood glucose because of inadequate amounts of circulating insulin.
INSULINLIKE GROWTH FACTORS:
Alternative name for somatomedins.
INTEGUMENT:
The skin.
INTERESTRUS:
Diestrus; the quiescent period between one heat period and the next.
INTERFERONS:
A specialized group of protein molecules capable of inhibiting virus replication and the growth of tumor cells, and of modulating the activities of certain components of the immune system.
INTERMEDIATE HOST:
A host that (usually) is essential to the life cycle of a parasite and in which the parasite undergoes development to juvenile but not mature stages.
INTERSEXUALITY:
Having characteristics of both sexes intermingling in the same individual.
INTERSTITIAL FLUID:
The fluid surrounding cells.
INTERVERTEBRAL DISKS:
Cartilaginous, cushioning structures positioned between the vertebrae of the spinal column.
INTOXICATION:
Poisoning.
INTRACRANIAL:
Within the skull.
INTRAMUSCULAR (IM):
A route of injection (into the muscle).
INTRAOCULAR PRESSURE:
The pressure within the eye.
INTROMISSION:
Insertion of the penis of the male into the vagina of the female during intercourse.
INTUBATION:
Insertion of a breathing tube into the trachea during anesthesia.
INTUSSUSCEPTION:
Prolapse (“telescoping”) of one section of bowel into an adjoining section.
INVOLUTION:
Period of repair in which there is a return to normal size and composition, as of the uterus following birth and expulsion of the placenta.
IONIZE:
To separate into ions (charged atoms).
IONIZING RADIATION:
Radiation capable of ionizing matter; examples include X rays and radioactive isotopes of elements such as radon, cesium, and strontium.
IRIDOCYCLITIS:
Inflammation of the iris and ciliary body of the eye.
IRIS (PLURAL: IRIDES):
The circular, pigmented structure located behind the cornea; by expanding or contracting its central opening, or pupil, it regulates the amount of light penetrating the inner reaches of the eye.
IRRITANT CONTACT DERMATITIS:
Uncommon inflammatory skin disease caused by direct contact with an irritating concentration of an offending substance.
ISCHEMIC INJURY:
Injury caused by loss of blood supply to a tissue.
ISLETS OF LANGERHANS:
The endocrine cells of the pancreas; the beta cells within the islets of Langerhans are the source of the critically important hormone insulin.
IXODID TICKS:
Hard-bodied ticks; distinguished from argasid (soft-bodied) ticks.
JACK:
A male donkey.
JAUNDICE:
Yellow discoloration of the skin and mucous membranes, caused by the deposition of bile pigment; most commonly a result of liver and/or bile-duct disease.
JEJUNUM:
The middle (and longest) portion of the small intestine, situated between the duodenum and the ileum.
JENNET:
A female donkey.
JOINT CAPSULE:
Thin, saclike structure that envelopes a joint and contains within it all the elements of the joint, such as the the articular cartilage, synovial membrane, synovial fluid, etc.
JUVENILE ARABIAN LEUKODERMA:
A depigmenting syndrome seen in young Arabian horses; also called Arabian fading syndrome and pinky syndrome.
KARYOTYPE:
A magnified photographic array of the chromosomes derived from an individual cell.
KERATECTOMY:
Surgical removal of a portion of the cornea.
KERATIN:
An insoluble, sulfur-rich protein that represents the principal component of skin, hair, and nails (hooves).
KERATINIZATION:
The process whereby keratinocytes in the epidermis mature to form the outer, horny layer of the skin.
KERATINOCYTES:
Skin cells that produce keratin; they are the major cell type of the epidermis, the outermost layer of the skin.
KERATITIS:
Inflammation of the cornea.
KERATOLYTIC:
Capable of causing softening and peeling of the outer (horny) layer of the skin.
KERATOMA:
Slowly growing tumor of the underlying structures of the hoof wall.
KETONE BODIES, KETONES:
Organic compounds produced by fatty acid and carbohydrate metabolism in the liver; elevated (toxic) levels are often produced in individuals with diabetes mellitus.
KETONURIA:
Spillage of ketone bodies (ketones) into the urine in diabetic ketoacidosis.
KICKING CHAINS:
Restraint device placed on the hind leg above the fetlock to discourage kicking.
KIDNEY:
Either of the two bean-shaped organs in the lower abdominal cavity that are responsible for filtering toxic waste products from the blood, producing the important hormone erythroipoietin, and maintaining the body’s water and electrolyte balance.
KILOCALORIE (KCAL):
Unit defined as the amount of energy required to raise the temperature of 1 kilogram of water 1 degree Celsius (centigrade); the “large” calorie; commonly called simply Calorie.
KILOGRAM:
One thousand grams (2.2 pounds).
LABIA:
The external lips or folds of the vulva of the female.
LABILE:
Chemically unstable; easily destroyed.
LACERATIONS:
Tears in the skin and underlying muscle.
LACRIMAL GLAND:
Tear gland.
LACTATED RINGER’S SOLUTION:
A sterile salt solution for (usually intravenous, but sometimes subcutaneous) administration containing sodium lactate, sodium chloride, potassium chloride, and calcium chloride; given to restore fluid and electrolyte balance.
LACTATION:
The production of milk by the mare.
LACTOSE:
Milk sugar.
LAGOPHTHALMOS:
An inability to close the eyelids completely.
LAMINITIS:
Inflammation of the laminae of the foot, which serve to attach the coffin bone to the hoof wall; also known as founder.
LANGERHANS CELLS:
Cells found in the epidermis, the outermost layer of the skin, that are important in generating immune responses in the skin.
LAPAROSCOPY:
Visual inspection of the interior of the abdominal cavity with a specialized instrument (a laparoscope), inserted through the body wall.
LARVAE (SINGULAR: LARVA):
Immature forms or stages in the life cycle of certain small animals, such as insects or parasites.
LARYNGEAL HEMIPLEGIA:
Paralysis affecting one side of the larynx, caused by damage to either of the two recurrent laryngeal nerves; also called roaring.
LARYNGITIS:
Inflammation of the larynx.
LARYNGOSCOPY:
Visual examination of the larynx.
LARYNX:
Muscular, cartilage-containing structure comprising the upper part of the respiratory tract between the pharynx and trachea, and containing the vocal chords; the “voice-box.”
LATENT INFECTION:
Dormant stage of certain infections during which the infectious agent is known to be present but is not actively replicating and cannot be detected by usual means.
LATERAL:
Closer to the side than to the midline of the body.
LAVAGE:
Irrigation or flushing out.
LAXITY:
Looseness.
LECITHIN:
Fatty acid-rich constituent of the outer surface of cell membranes; also called phosphatidylcholine.
LEIOMYOMA:
Benign tumor of smooth muscle cells.
LEIOMYOSARCOMA:
Malignant tumor of smooth muscle cells.
LENS:
Transparent refractive structure that finely focuses images onto the retina for clear and sharp vision.
LEPTOSPIRES:
Spiral-shaped bacteria belonging to the spirochete group.
LEPTOSPIROSIS:
Bacterial disease caused by leptospires (spiral-shaped bacteria).
LESION:
Any disease-induced abnormality of tissue structure or tissue function.
LETHARGY:
An abnormal state of drowsiness or dullness.
LEUKOCORIA:
A whitening of the pupil of the eye.
LEUKOCYTES:
White blood cells.
LEUKOCYTOSIS:
Increase in the number of circulating white blood cells.
LEUKODERMA:
Whitening of the skin, often in localized patches.
LEUKOENCEPHALOMALACIA:
Degenerative brain disorder, apparently caused by a toxin produced by the mold Fusarium moniliforme; also called cornstalk disease, moldy corn poisoning, forage disease, and blind staggers.
LEUKOPENIA:
Reduction in the number of circulating white blood cells.
LEUKOTRICHIA:
Abnormal whitening of the hair, often in localized patches.
LEUKOTRIENES:
Compounds that act as modulators of allergic and inflammatory reactions.
LEYDIG CELLS:
Specialized cells in the testes that produce the male sex hormone testosterone.
LIBIDO:
Sexual drive.
LIGAMENT:
Strengthening band of fibrous tissue, for supporting and stabilizing a joint structure.
LIGATE:
To bind or tie off.
LIMBUS:
The line of demarcation between the cornea and sclera of the eye.
LINOLEIC ACID:
An essential fatty acid acquired from vegetable sources; important in the biosynthesis of cell membranes.
LIPASE:
An enzyme that breaks down fat.
LIPID FILM:
A layering of fat.
LIPID(S):
Fat(s).
LIPIDOSIS:
Abnormal accumulation of fat within cells.
LIPOMA:
Benign tumor of fat cells.
LIPOSARCOMA:
Malignant tumor of fat cells.
LOBULATED:
Divided into small lobes or lobules.
LOCKJAW:
Synonym for trismus, a clinical sign of tetanus.
LOCUS (PLURAL: LOCI):
The site on a chromosome where a specific gene is located.
LORDOSIS:
Downward curvature of the lumbar spine; “swayback.”
LOW RINGBONE:
Ringbone affecting the coffin joint.
LUMBOSACRAL:
Pertaining to the lower back region
LUMEN:
The interior of a blood vessel or tubular organ, such as the intestine.
LUTEAL PHASE:
In the reproductive cycle, the period during which the ovarian follicle converts to a corpus luteum and secretes the hormone progesterone.
LUTEINIZATION:
Conversion of the ovarian follicle to a corpus luteum.
LUTEINIZING HORMONE (LH):
Hormone produced by the pituitary gland; together with follicle-stimulating hormone (FSH) it assists in causing ovulation and inducing production of the hormone estrogen.
LUXATION:
Dislocation of a joint; also, total displacement of the lens of the eye from its normal position.
LYME BORRELIOSIS, LYME DISEASE:
An infectious arthritis of people and dogs caused by a spirochete bacterium, Borrelia burgdorferi; whether this organism is the cause of any significant disorder in horses remains controversial at this time.
LYMPH:
Generally clear fluid drained from tissues, that circulates within the lymphatic vessels and contains fats, proteins, and specialized cells (lymphocytes).
LYMPH NODE:
Any of the body’s many nodular accumulations of lymphoid cells; they are interconnected by means of lymphatic vessels.
LYMPHADENITIS:
Inflammation of one or more lymph nodes.
LYMPHADENOPATHY:
Enlargement of one or more lymph nodes, as from inflammation, infection, or cancer.
LYMPH-NODE ASPIRATE:
Sample of fluid and cells from deep within a lymph node, obtained using a needle and syringe.
LYMPHOCYTE:
A type of white blood cell capable of responding to the presence of foreign material in the body; lymphocytes play a central role in directing and coordinating immune responses.
LYMPHOCYTIC THYROIDITIS:
Immune-mediated inflammation of the thyroid gland.
LYMPHOCYTOSIS:
Abnormal increase in the number of circulating lymphocytes.
LYMPHOMA, LYMPHOSARCOMA:
Malignant tumor of lymphocytes.
MACERATION:
Softening or dissolution of skin cell layers, resulting from overexposure to moisture or topical medications.
MACROPHAGE:
A specialized white blood cell of central importance to the body; it ingests cellular debris and foreign material, destroys ingested microorganisms, processes ingested antigens as an initial step in the induction of a specific immune response, and synthesizes a number of important enzymes, coagulation factors, and messenger molecules; also referred to as a mononuclear phagocyte.
MACULE:
A discolored area of skin that is not elevated above the skin surface.
MALABSORPTION:
Faulty absorption of nutrients by the intestine.
MALASSIMILATION:
Defective transport of one or more nutrients from the intestinal contents across the intestinal wall.
MALDIGESTION:
Faulty digestion.
MALIGNANT:
Capable of spreading and invading other tissues; said of tumors.
MAMMARY GLAND:
Breast.
MANDIBLE:
The lower jaw.
MANE-CHEWING:
A stable vice exhibited primarily by yearlings and two-year-olds.
MANIA:
Frantic behavior.
MAST CELL:
A specialized, granule-containing cell found in the skin and lining of the inner body surfaces; it plays a central role in the development of allergy.
MASTICATION:
The action of chewing.
MASTITIS:
Inflammation of one or more mammary glands.
MASTOCYTOSIS:
Abnormal infiltration of mast cells into a body tissue.
MATERNAL IMMUNITY:
A form of temporary immunity that is passed from the mare to the foal in utero (in the uterus) and/or after birth in the colostrum and milk; primarily antibody, maternal immunity serves to protect the foal until its own immune defenses become fully operative.
MAXILLA:
The upper jaw.
MECHANICAL VECTOR:
A vector that merely serves physically to transport a parasite from one host to another.
MECONIUM:
The contents of the foal’s first bowel movement.
MEDIAL:
Closer to the midline of the body.
MEDIAL CANTHUS:
The inner corner of the eye.
MEDULLA:
The innermost part of an organ (kidney, adrenal gland, brain) or hair shaft; contrasted with cortex.
MEGACALORIE (MCAL):
One thousand kilocalories; a useful term for quantifying the energy in a ration.
MEGAKARYOCYTE:
A giant cell found in the bone marrow; it is the precursor of the blood platelets.
MEIOSIS:
Process involved in the formation of gametes (reproductive cells), wherein cell division produces new cells (spermatozoa and ova) containing only one set of chromosomes.
MELANIN:
Dark pigment of skin and hair.
MELANOBLASTS:
Immature melanin-forming cells that originate early in fetal life.
MELANOCYTES:
Cells of the epidermis, the outermost layer of the skin, that produce the skin pigment melanin.
MELANOCYTE-STIMULATING HORMONE (MSH):
Hormone produced by the pituitary gland that mediates the deposition of melanin (dark pigment of skin and hair) in the body.
MELANOMA:
A (usually) malignant tumor of pigmented skin cells.
MELANOTRICHIA:
Abnormal darkening of the hair color.
MELENA:
Dark, pitchy stool caused by bleeding into the digestive tract.
MELIOIDOSIS:
A glanderslike disease caused by Pseudomonas pseudomallei, characterized by the development of nodules in internal organs; not known to occur in the United States.
MENINGES:
The three protective membranes surrounding the brain and spinal cord; specifically, the dura mater, pia mater, and arachnoid.
MENINGITIS:
Inflammation of the meninges.
MERONT:
Alternative term for schizont.
MEROZOITES:
The daughter cells resulting from either schizogony or endodyogeny (asexual forms of reproduction in certain protozoa).
MESENTERIC:
Pertaining to the mesentery, the membrane that lines the abdominal organs and attaches them to the body wall.
MESOVARIUM:
Fold of tissue that holds the ovaries in place.
METABOLIC ENERGY (ME):
The caloric content of a diet; can be roughly estimated from the proximate analysis.
METABOLIC WATER:
Water the body obtains from solid food and the breakdown of ingested fat, carbohydrate, and protein.
METABOLISM:
All the life-sustaining biochemical processes in the body; the conversion of nutrients into energy.
METABOLITES:
By-products of metabolism.
METABOLIZABLE ENERGY (ME):
The difference between the gross energy of a food and the energy that is lost in urine and feces.
METACERCARIA:
Infective larval form of flukes that arises from the cercaria stage.
METAPHYSIS:
The region immediately beneath the growth plate (epiphysis) of a bone.
METASTASIS:
Spread of tumor cells from the primary tumor site to distant body sites; a characteristic of malignant tumors.
METESTRUS:
In the estrus cycle, the period of subsidence of follicular activity that follows estrus (“heat”).
METRITIS:
Inflammation of the uterus.
MICROBE:
Any minute living organism, particularly one capable of causing disease; viruses, because they are not living organisms, technically are not considered “microbes,” but are more correctly referred to by a term such as “infectious agent.”
MICROVASCULATURE:
The smallest blood vessels (capillaries).
MILLER’S DISEASE:
Colloquial term for nutritional secondary hyperparathyroidism.
MINERALOCORTICOIDS:
Corticosteroids whose primary function is regulation of water and electrolyte balance; they act by retaining sodium and excreting potassium within the kidney tubules.
MINIMAL INHIBITORY CONCENTRATION (MIC):
Laboratory test procedure for determining the sensitivity or resistance of a bacterial isolate to several antibiotics.
MIOTIC:
Any ophthalmic medication that causes the pupil to contract.
MIRACIDIUM:
Free-living larval form in the life cycle of flukes.
MITICIDE:
Any medication that kills mites.
MITOCHONDRIA (SINGULAR: MITOCHONDRION):
Specialized structures within body cells that are responsible for producing energy.
MITOSIS:
Process wherein a body cell divides into two exact copies of itself, each new cell receiving two complete sets of chromosomes.
MITOTIC:
Actively undergoing cell division.
MITRAL REGURGITATION:
Partial backflow of blood through a dysfunctioning mitral valve.
MITRAL VALVE:
The atrioventricular valve on the left side of the heart.
modified-live virus:
Attenuated (weakened) virus that no longer produces clinical disease in the host but retains the ability to induce a protective immune response, and can be used as a vaccine; technically a misnomer, since viruses are not living organisms.
MOLARS:
The large grinding teeth.
MOLDY CORN POISONING:
Common name for leukoencephalomalacia.
MONENSIN:
Feed additive for cattle and poultry; toxic for horses.
MONOCULAR FIXATION:
Focusing of one eye on an object.
MONOCYTE:
Nondescript white blood cell found in the circulation, which converts into an active macrophage upon entry into tissue.
MOON BLINDNESS:
Periodic ophthalmia.
MORPHOGENESIS:
The progressive development of form and shape of an organism, or of an individual organ or tissue within the organism.
MORPHOLOGY:
The shape and structure of an organ or of an entire organism.
MOTILE:
Capable of movement.
MOTILITY:
Ability to move.
MOTONEURON:
A nerve cell that supplies myofibers in skeletal muscle.
MOTOR UNIT:
The basic functional and anatomical organization of nerves and muscle fibers within skeletal muscle.
MUCOCILIARY ESCALATOR:
A coordinated and forceful wavelike movement of the cilia lining the air passageways from the trachea to the bronchioles; essential for the normal removal of mucus and inhaled particulate matter and bacteria.
MUCOCUTANEOUS JUNCTIONS:
Areas where mucous membranes and skin adjoin, such as the lip margins.
MUCOID:
Resembling mucus.
MUCOMETRA:
Presence of mucus in the uterus.
MUCOSAL-ASSOCIATED LYMPHOID TISSUE (MALT):
Lymphoid tissue associated with the linings of the digestive, respiratory, and urogenital tracts.
MUCOUS MEMBRANES:
Lubricating membranes lining the internal surfaces of body cavities, such as the mouth, digestive tract, respiratory tract, and urinary tract.
MUCUS:
Slimy substance secreted by certain membranes (mucous membranes); contains a variety of secretions, salts, and cells.
MULTILOCULAR:
Having many compartments.
MULTIPLE MYELOMA:
An uncommon malignant tumor of plasma cells arising from the bone marrow.
MURMUR:
An abnormal heart sound produced when blood flows too rapidly or too chaotically through a portion of the heart; a common sign of heart disease.
MUTATION:
A permanent genetic change, sometimes resulting in altered structure or function.
MYCETOMA:
General term for a swollen, progressing, tumorlike skin lesion caused either by fungi or certain bacteria.
MYCOLOGY:
The study of fungi.
MYCOPLASMAS:
Microscopic organisms closely related to bacteria that are ubiquitous inhabitants of the respiratory and genital tracts.
MYDRIATIC:
Any ophthalmic medication that dilates the pupil.
MYELIN:
Fatty substance forming the outer tunic (myelin sheath) around many nerve axons; facilitates the conduction of nerve impulses along the axons.
MYELOGENOUS:
Originating within the bone marrow.
MYELOPATHY:
General term for any degenerative disorder affecting the spinal cord.
MYIASIS:
Infestation of body tissue by fly maggots.
MYOCARDITIS:
Inflammatory heart-muscle disease.
MYOCARDIUM:
The muscular layer of the heart; heart muscle.
MYOCLONUS:
Involuntary rapid, jerky twitching or contraction of muscles.
MYOFIBERS:
Muscle fibers.
MYOFIBRILS:
Slender threadlike structures, bundles of which make up each muscle fiber.
MYOFILAMENTS:
Smaller threadlike elements making up the myofibrils of muscles.
MYOGLOBIN:
The oxygen-transporting pigment of muscle tissue.
MYOGLOBINURIA:
Presence of myoglobin in the urine.
MYONECROSIS:
Muscle-cell death.
MYOPATHY:
General term for any muscle disorder.
MYOSIN:
A vital protein component of muscle, one of the proteins responsible for muscle contraction.
MYOSITIS:
Muscle inflammation.
NANOGRAM:
One billionth of a gram.
NARES (SINGULAR: NARIS):
The two halves of the nasal passages; also, the external and internal openings of the nasal passages.
NASAL SEPTUM:
Vertical dividing wall that separates the two nasal passages or nares.
NASAL TURBINATES:
Delicate, scroll-like, rolled bony structures within the nasal cavity that filter, warm, and humidify inhaled air; also referred to simply as turbinates.
NASOPHARYNX:
The rear portion of the pharynx, above the soft palate.
NATURAL KILLER (NK) CELLS:
Specialized lymphocytes that are important in detecting and eliminating tumor cells and virus-infected cells.
NAVICULAR DISEASE:
Lameness caused by damage to the navicular bone; one of the most common causes of intermittent forelimb lameness in the horse.
NECROLYSIS:
Separation or peeling of tissue caused by cell death.
NECROPSY:
Examination of an animal after death; postmortem; autopsy on an animal.
NECROSIS:
Cell death.
NECROTIC:
Composed of dead cells.
NECROTIZING:
Causing cell death.
NEGATIVE REINFORCEMENT:
In training, the use of an unpleasant stimulus, such as a whip or bit, if a task is not performed.
NEGRI BODIES:
Intracellular inclusion bodies sometimes found in brain cells of animals or humans with rabies.
NEMATODE:
General term for a roundworm.
NEONATAL:
Newborn.
NEONATAL ISOERYTHROLYSIS:
Acute hemolytic anemia of the newborn caused by ingestion of antibodies in the mare’s colostrum and milk that are directed against the neonate’s red blood cells; also called hemolytic disease of the newborn.
NEONATAL MALADJUSTMENT SYNDROME:
Disease or group of diseases of foals characterized by progressive neurologic dysfunction.
NEOPLASIA:
Uncontrolled, progressive proliferation of cells under conditions that normally should be restrictive of cell growth; formation of a tumor.
NEOPLASM:
Tumor.
NEOVASCULARIZATION:
Growth of new blood vessels into an abnormal site, such as a tumor.
NEPHRITIS:
Kidney inflammation.
NEPHROLITH:
Kidney stone.
NEPHRONS:
The microscopic, functional units of the kidney.
NEPHROSCLEROSIS:
Scarring of kidney tissue; a principal cause of the normal, progressive deterioration of kidney function that accompanies aging.
NEPHROTIC SYNDROME:
Abnormal fluid retention as edema or ascites, resulting from glomerular disease of the kidneys.
NERVOUS TUNIC:
Retina; innermost layer of the eye.
NEURECTOMY:
Surgical cutting of a nerve to relieve pain.
NEURITIS:
Inflammation of a nerve.
NEUROFIBROMA:
Benign tumor of the nervous system arising from Schwann cells.
NEUROMA:
Tumor arising from a nerve.
NEUROMUSCULAR JUNCTIONS:
The intimate connections between muscle cells and adjacent nerve cells, representing a specialized extension of the sarcolemma.
NEUROMYOPATHY:
General term for any disorder affecting both neurons and muscle fibers.
NEURON:
An individual nerve cell.
NEUROPATHY:
Any disorder of the peripheral nervous system.
NEUROTOXIN:
Any toxin targeting the nervous system.
NEUTROPENIA:
An abnormal decrease in the number of circulating neutrophils.
NEUTROPHIL:
A type of white blood cell capable of engulfing and destroying bacteria and other disease agents, immune complexes, and cell debris.
NEUTROPHILIA:
An abnormal increase in the number of circulating neutrophils.
NIT:
Louse egg.
NOCARDIOSIS:
Bacterial infection caused by members of the genus Nocardia; in horses Nocardia is most often a cause of local wound infections.
NODULAR:
Characterized by nodules.
NODULAR NECROBIOSIS:
Equine collagenolytic granuloma.
NODULE:
A large papule; small lump.
NOSOCOMIAL INFECTION:
An infection acquired in the hospital environment.
NUCHAL LIGAMENT:
A large, strong band of connective tissue that provides support for the neck.
NUCLEIC ACIDS:
General term for deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), DNA serving as the genetic material of all living organisms and some viruses.
NUCLEOTIDE:
An individual unit of DNA.
NULLIPAROUS:
Having never given birth.
NUTRITIONAL SECONDARY HYPERPARATHYROIDISM:
Disease caused by an imbalance in the quantities of calcium and phosphorus in the diet, resulting in a net withdrawal of calcium from the bones; also called “big head” or “millers’ disease.”
NYSTAGMUS:
Rapid, involuntary, rhythmic eye movements, often indicative of central nervous system dysfunction.
OBLIGATORY PARASITE:
A parasite whose life cycle cannot be completed without a parasitic phase at some stage.
OCCLUDE:
To close off or obstruct.
OCCLUSION:
The fit or “bite” of the upper and lower teeth together when in contact following closure of the mouth.
OCULAR:
Pertaining to the eyes.
OLECRANON:
The point of the elbow.
OLECRANON BURSITIS:
Bursitis caused by repeated trauma to the point of the elbow; also called shoe boil.
OLFACTORY:
Pertaining to smell.
OLFACTORY NERVES:
Nerves found in the nasal turbinates in which the sense of smell originates.
OLIGURIA:
Reduction in the amount of urine excreted.
OMPHALOPHLEBITIS:
Infection (usually bacterial) of the veins of the umbilical cord in the newborn; “navel ill.”
ONCOGENESIS:
The process of tumor development.
ONCOLOGIST:
Cancer specialist.
OOCYST:
An encapsulated ovum (egg) of a sporozoan parasite such as Toxoplasma gondii, usually excreted in the feces.
OOCYTE:
Developing egg cell (ovum) in the ovary.
OPACIFICATION:
Loss of transparency.
OPACITY:
An opaque area or spot, as in the lens or cornea of the eye.
OPEN REDUCTION:
Any procedure to repair a fracture wherein the broken bone is exposed surgically.
OPERANT CONDITIONING:
“Trial and error” learning, usually involving a reward.
OPHTHALMOSCOPE:
Instrument for viewing the interior of the eye.
OPPORTUNISTIC PATHOGEN:
Any organism that is able to induce disease only if the host’s immune or other defenses are compromised.
OPTIC DISK:
That portion of the optic nerve visible at the surface of the retina; also called optic nerve head.
OPTIC NERVE:
Literally an extension of the brain, which reaches to the back of the eye (retina) and transmits signals derived from light energy that are translated into a visual image by the brain.
OPTIC NEURITIS:
Inflammation of the optic nerve.
ORCHITIS:
Inflammatory disease of the testicle.
ORGAN OF CORTI:
The spiral-shaped organ of hearing within the inner ear, containing specialized sensory receptors.
OROPHARYNX:
The back of the throat; tonsillar area, between the soft palate and epiglottis.
OSSELETS:
Puffiness around the fetlock joint.
OSSEOUS:
Bony.
OSSICLES:
Very small bones.
OSSIFICATION:
The formation of bone.
OSSIFYING MYOPATHY:
Condition most commonly affecting the hindlimbs of the horse, in which scarring and/or bone formation occurs within injured muscles.
OSTEITIS:
Inflammation of a bone.
OSTEOBLAST:
A bone-forming cell.
OSTEOCHONDRITIS DISSECANS (OCD):
Cartilage disorder characterized by the presence of large flaps of cartilage or loose cartilaginous bodies within a joint.
OSTEOCHONDROSIS:
A disorder of growing cartilage that may affect either the growth plate or the articular cartilage.
OSTEOCYTE:
Cell type in bone that, in response to certain hormones, is responsible for maintaining normal calcium and phosphorus levels in the bloodstream.
OSTEOMYELITIS:
Infection of a bone accompanied by pus formation; usually caused by bacteria.
OSTEOPENIA:
Loss of bone calcium.
OSTEOPOROSIS:
Thinning and weakening of bone.
OSTEOSARCOMA:
A malignant tumor of bone.
OSTEOTOMY:
Surgical cutting of bone.
OTITIS EXTERNA:
Inflammation of the outer ear.
OTITIS INTERNA:
Inflammation of the inner ear; also called labyrinthitis.
OTITIS MEDIA:
Inflammation of the middle ear; also called tympanitis.
OVARIAN FOLLICLE:
An ovum (egg) and its surrounding cells.
OVARIECTOMY:
Surgical removal of one or both ovaries.
OVARIES:
Paired organs of the female responsible for the production of ova (eggs).
OVARIOHYSTERECTOMY:
Surgical removal of the uterus and ovaries.
OVERO:
Recessive equine coat-color pattern, consisting of a colored base coat with white patches and colored legs. The white markings are more irregular than the colored patches of the tobiano. White does not cross the back and the head is mostly white.
OVIDUCTS:
Uterine or fallopian tubes.
OVOTESTES:
Abnormal gonads containing both testicular and ovarian tissue.
OVULATION:
Release of an egg from an ovary.
OVUM (PLURAL: OVA):
Egg.
OXIDATION:
The cellular “burning” of glucose, amino acids, and fatty acids to produce energy in the form of adenosine triphosphate (ATP), the major form of energy used by cells.
OXYGENATED:
Filled with oxygen; said of arterial blood.
OXYTOCIN:
A hormone formed in the hypothalamic region of the brain and stored in the pituitary gland; it stimulates contraction of the uterus and milk ejection from the mammary glands.
PACEMAKER:
Nerve tissue that controls the heart’s rate of contraction and relaxation; also known as the sinoatrial node. An artificial pacemaker is an electrical device implanted surgically to treat abnormally slow heart rhythms (bradycardias).
PACKED CELL VOLUME (PCV):
A measurement of the volume of red blood cells in relation to the volume of blood fluid, expressed as a percentage; also called the hematocrit.
PALLIATION:
Alleviation of clinical signs in the absence of specific treatment of the underlying disorder.
PALMAR DIGITAL NEURECTOMY:
Permanent nerve block performed to relieve navicular disease.
PALPABLE:
Detectable by touch or feeling.
PALPATE:
To examine by feeling with the hands and fingers.
PALPEBRAL:
Pertaining to an eyelid.
PALSY:
Paralysis.
PANCYTOPENIA:
Condition wherein red blood cell, white blood cell, and platelet cell numbers are all decreased in the circulation.
PAPILLEDEMA:
Swelling of the optic nerve.
PAPILLOMA:
Wart.
PAPULE:
A minute, firm, well-demarcated elevation of the skin.
PARALYSIS:
Total absence of voluntary movement in a muscle or set of muscles.
PARANASAL SINUSES:
Nasal chambers that act to filter, warm, and humidify incoming air.
PARASITE:
Any organism that is dependent in some manner for its continued existence on another organism (its host), most often to the detriment of the host.
PARASITEMIA:
Presence of a parasite in the blood circulation.
PARASITOLOGY:
The study of parasites.
PARATENIC HOST:
An “optional” host in a parasite’s life cycle in which juvenile stages may persist but do not develop.
PARATHYROID GLANDS:
Twin, small pairs of endocrine glands located adjacent to the thyroid gland; they secrete parathyroid hormone (PTH), which is essential for the regulation of calcium and phosphorus balance in the body.
PARATHYROID HORMONE (PTH):
Hormone secreted by the parathyroid glands that regulates the metabolism of calcium and phosphorus in the body.
PARENTERAL:
By injection (i.e., not by the oral route); injectable.
PARESIS:
Diminished ability to move a muscle or a body part voluntarily.
PARIETAL PLEURA:
Thin transparent membrane that forms the inner lining of the chest cavity.
PAROXYSM:
A sudden bout.
PARROT MOUTH:
Dental malformation consisting of an overshot jaw; actually caused by a shortening of the lower jaw.
PARTURITION:
The act of giving birth.
PASTERN FOLLICULITIS:
The most commonly encountered pus-forming skin infection in the horse, caused by Staphylococcus aureus.
PASTERN JOINT:
The joint between the short pastern bone and the long pastern bone.
PATCH:
A large macule.
PATELLA:
Knee cap, a small triangular sesamoid bone located in front of the knee.
PATELLAR LUXATION:
Congenital displacement of the knee-cap (patella); rare in horses.
PATENT:
Unobstructed, open.
PATENT DUCTUS ARTERIOSUS (PDA):
Abnormal persistence after birth of an embryonic blood vessel connecting the pulmonary artery to the aorta; only rarely seen in horses.
PATENT INFECTION:
With regard to parasites, an infection in a definitive host that results in the appearance of products of the parasite’s reproduction (eggs, larvae, etc.).
PATENT URACHUS:
Abnormal persistence of the urachus after birth.
PATHOGEN:
Any microbial agent capable of causing disease.
PATHOGENESIS:
The cellular, biochemical, and pathological mechanism(s) underlying the development of a disease.
PATHOGENIC:
Able to cause disease.
PATHOGENICITY:
The relative ability of an organism to cause disease.
PEDAL OSTEITIS:
Increased vascularization and demineralization affecting the coffin bone, usually secondary to inflammation resulting from repeated, excessive concussion on the sole.
PEDICLE:
A small stalk or stem.
PEDUNCULATED:
Situated on a stalk.
PELVIC FLEXURE:
Area of the large intestine where the intestine narrows and folds back on itself.
PELVIC SYMPHYSIS:
The joint formed by the union of the two halves of the pubic bone of the pelvis.
PELVIS:
Hip.
PEMPHIGUS FOLIACEUS:
Autoimmune skin disease characterized by autoantibody production and the subsequent development of vesicles and pustules in the superficial layers of the skin.
PENICILLINS:
A large group of antibiotics derived primarily from fungi of the genus Penicillium; of pivotal importance in the treatment of diseases caused by certain bacteria such as the streptococci, clostridia, and spirochetes, penicillins interfere with the vital synthesis of bacterial cell walls.
PEPTIDE:
A short chain of amino acids; peptides form the building blocks of proteins.
PEPTIDE HORMONES:
Hormones manufactured by the body from amino acids, sometimes with the addition of carbohydrates (sugars).
PERACUTE:
Of extremely rapid onset.
PERCUTANEOUS NEEDLE BIOPSY:
Technique by which a sample of organ tissue is obtained for examination by maneuvering a biopsy needle through the skin and into the organ of interest.
PERIANAL:
In the region of the anus.
PERICARDIAL EFFUSION:
Abnormal accumulation of fluid in the pericardial sac.
PERICARDITIS:
Inflammation or infection of the pericardium.
PERICARDIUM:
The thin, membranous sac that surrounds the heart, stabilizing its position and protecting it from disease affecting nearby structures.
PERINATAL PERIOD:
The period shortly before and after birth.
PERINEUM:
Region between the thighs encompassing the anus and genitalia.
PERIOCULAR:
Pertaining to the area around the eye.
PERIODIC OPHTHALMIA:
Recurrent inflammation of the eye associated with an abnormal immunologic reaction to leptospires (spiral-shaped bacteria) or threadworms; also known as recurrent uveitis or moon blindness.
PERIODONTAL LIGAMENT:
Structure composed of tiny fibers that serves to attach the tooth root to the bone of the jaw.
PERIORBIT:
Eye socket.
PERIOSTEAL STRIPPING:
The most common surgery for correction of angular limb deformities in foals.
PERIOSTEUM:
The highly sensitive connective tissue sheathing the bones; it contains a rich blood supply and provides for the nutrition, growth, repair, and protection of the underlying bone.
PERIPHERAL NERVOUS SYSTEM (PNS):
The cranial, spinal, and peripheral nerves and their connections to muscle or to sensory receptors.
PERISTALSIS:
Muscular movements of the intestinal tract that function to propel contents longitudinally through the tract.
PERMEABILITY:
Leakiness; ability to be penetrated.
PH:
A measure of the hydrogen ion concentration of a solution, reflective of acidity (pH below 7) or alkalinity (pH above 7), with a pH value of 7 representing neutrality.
PHAEOHYPHOMYCOSIS:
An uncommon chronic infection of the subcutaneous tissues caused by dark, pigmented fungi (dematiaceous fungi).
PHAGOCYTE:
Any cell type (such as a neutrophil or macrophage) able to engulf and digest minute particulate matter.
PHALANX (PLURAL: PHALANGES):
General term for any bone forming part of a finger or toe.
PHARYNGEAL:
Pertaining to the pharynx.
PHARYNGITIS:
Inflammation of the pharynx; “sore throat.”
PHARYNX:
Area extending from the rear of the mouth and nasal passages to the larynx and esophagus.
PHENOTYPE:
The visible, physical expression of a genetic trait, e.g., blue eyes or red hair.
PHEROMONES:
Chemical secretions that elicit a specific behavioral response (often attraction) in another individual of the same species.
PHLEBITIS:
Inflammation of a vein.
PHLEBOTOMY:
Therapeutic blood-letting.
PHLEGM:
Viscous secretion produced by the respiratory tract.
PHOSPHOLIPIDS:
Fats containing phosphorus.
PHOTOAGGRAVATED VASCULITIS:
Specific disease unique to horses, characterized by an inflammation of blood vessels (vasculitis) that appears to be “triggered” and subsequently aggravated by exposure to sunlight.
PHOTON:
The energy unit of visible light, having characteristics both of a wave as well as a discrete particle.
PHOTOPERIOD:
The length of time per day that an animal is exposed to natural or artificial light.
PHOTOPHOBIA:
Visual hypersensitivity to light.
PHOTORECEPTORS:
Specialized light receptors (rods and cones) present in the retina of the eye.
PHOTOSENSITIZATION:
Clinical syndrome resulting from excessive exposure to ultraviolet radiation (sunlight).
PHYCOMYCOSIS:
General term describing several tropical and subtropical diseases caused by different organisms, including Basidiobolus haptosporus (causing basidiobolomycosis), Conidiobolus coronatus (causing conidiobolomycosis), and Pythium insidiosum (causing pythiosis).
PHYSIOLOGY:
The study of body function and metabolism.
PHYSIS (PLURAL: PHYSES):
A growth plate of a bone; an area where new bone growth originates.
PHYSITIS:
Generalized bone disease of young growing horses, characterized by enlargement of the growth plates of certain long bones and of the vertebrae of the neck.
PHYTATES:
Form of inositol (a sugarlike compound) found in plants; excessive amounts in the diet can interfere with the absorption of zinc from the digestive tract.
PICOGRAM:
One trillionth of a gram.
PIEBALD:
Black and white (horse coloration).
PINKY SYNDROME:
Juvenile Arabian leukoderma.
PINNA:
The external portion or flap of the ear.
PITUITARY GLAND:
Endocrine gland located at the base of the brain, and connected to it by a narrow stalk; it stores and/or secretes many hormones of pivotal importance to body function, including growth hormone (GH), thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), oxytocin, prolactin, antidiuretic hormone (ADH, vasopressin), and adrenocorticotropic hormone (ACTH).
PLACENTA:
The organized tissue in the uterus joining the fetus to the mother.
PLACENTITIS:
Inflammation of the placenta.
PLANTAR LIGAMENT:
Ligament that courses along the back of the calcaneus bone in the hock.
PLAQUE:
The mixture of oral bacteria, bacterial sugars, salivary proteins, and food and cellular debris, that accumulates on the teeth; also, a flat area in the skin.
PLASMA:
The fluid portion of the blood (excluding the blood cells).
PLASMA CELLS:
End-stage B lymphocytes (B cells), whose function is to produce antibodies.
PLATELETS:
Cell fragments released from megakaryocytes, that play an important role in blood clotting.
PLEURA:
Thin, transparent membrane covering the lungs and lining the chest cavity.
PLEURAL CAVITY:
The potential space between the visceral pleura and parietal pleura.
PLEURAL EFFUSION:
Excessive fluid accumulation in the pleural cavity.
PLEURITIS:
Inflammation of the pleura.
PLEUROPNEUMONIA:
Bacterial infection secondary to pneumonia or lung abscesses.
PNEUMONIA:
An inflammatory condition of the lungs; characterized by the filling of air spaces with fluid, resulting in impaired gas exchange.
PNEUMOTHORAX:
Accumulation of air within the pleural cavity, inside the chest but outside the lungs, impeding the ability of the lungs to expand normally; collapsed lung.
PNEUMOUTERUS:
Accumulation of air inside the uterus; a consequence of pneumovagina.
PNEUMOVAGINA:
Aspiration of air and debris into the vagina; also known as wind-sucking.
POLL:
The back of the head.
POLLAKIURIA:
Increased frequency of urination.
POLYCLONAL GAMMOPATHY:
Increase in serum gamma globulins (blood proteins that include most of the antibody classes) that tends to be spread over a wide range of protein types.
POLYCYTHEMIA:
An excessive number of red blood cells.
POLYDIPSIA:
Excessive thirst.
POLYESTROUS:
Having more than a single estrous cycle per year.
POLYGENIC TRAITS:
Traits that are the result of the action of more than a single gene.
POLYMORPHISM:
Genetic variation.
POLYMORPHONUCLEAR LEUKOCYTE:
Any white blood cell having a lobular nucleus, such as a neutrophil.
POLYNEURITIS:
Inflammation occurring simultaneously in more than one nerve.
POLYP:
A small fleshy mass projecting from the surface of a mucous membrane.
POLYPEPTIDE:
Any peptide containing two or more amino acids; often referred to simply as a peptide.
POLYPHAGIA:
Excessive eating.
POLYSYNOVITIS:
Inflammation of the lining membrane of a joint.
POLYURIA:
Excessive urination.
POSITIVE REINFORCEMENT:
In training, giving a reward such as food for suitable behavior.
POSTERIOR CHAMBER:
That portion of the eye between the iris and the lens.
POSTERIOR PARESIS:
Partial paralysis of either or both hind limbs.
POSTHITIS:
Inflammation of the prepuce.
POSTPARTUM:
Occurring after birth.
POSTPRANDIAL:
Occurring after a meal.
POTOMAC HORSE FEVER:
A gastrointestinal disease of horses, characterized by high fever, colitis (inflammation of the large intestine), diarrhea, and dehydration; caused by a rickettsia, Ehrlichia risticii
POULTICE:
Soft, often medicated paste spread on a cloth and draped over a wound.
PREDILECTION:
Preference.
PREMUNITION:
Maintenance of immunity to a parasite by the persistent presence of small numbers of the parasite, usually in the gastrointestinal tract; premunition immunity wanes if the parasite is completely eliminated from the body.
PREPATENT PERIOD:
The time elapsing between the initiation of a parasite’s infection of a definitive host and the appearance of the products of parasite reproduction, e.g., eggs, larvae, etc.
PREPUBERTAL:
Pertaining to the period before sexual maturity.
PREPUCE:
Fold of skin enclosing the penis; also called the sheath.
PRICKLE CELL LAYER:
A layer of cells within the epidermis, the outermost layer of the skin; also known as the squamous cell layer, it lies above the basal cell layer and below the granular cell layer.
PRIMARY HYPERPARATHYROIDISM:
Hyperparathyroidism resulting from excessive, relatively uncontrolled secretion of parathyroid hormone (PTH) by one or more abnormal parathyroid glands.
PRIMARY HYPOPARATHYROIDISM:
Hypoparathyroidism resulting from an absolute or relative deficiency of secretion of parathyroid hormone (PTH).
PRIMARY LYMPHOID ORGANS:
Organs in which the production and maturation of lymphocytes takes place; in horses they include the bone marrow, the mucosal-associated lymphoid tissue (MALT), and the thymus.
PROESTRUS:
In the estrus cycle, the period just before estrus.
PROGESTERONE:
Hormone secreted by the corpus luteum, adrenal cortex, and placenta, whose primary function is to prepare the uterus for pregnancy; also called progestin.
PROGESTOGEN:
Any compound with progesteronelike activity.
PROGLOTTID:
One of the chain of segments comprising the strobila or body of a tapeworm parasite.
PROGNATHISM:
Condition characterized by an elongated lower jaw.
PROGNOSIS:
The outlook for recovery from a disease.
PROLACTIN:
Hormone secreted by the pituitary gland that simulates and sustains lactation; also called lactogenic hormone.
PROLAPSE:
A bulging through or protrusion of a tissue or organ.
PROLIFERATIVE OPTIC NEUROPATHY:
An incidental finding in old horses, consisting of excessive tissue growth in the area of the optic disk (at the back of the eye).
PROPHYLAXIS:
Disease prevention.
PROPTOSIS:
Bulging or protrusion of the eyeball from the eye socket; also called exophthalmos.
PROPULSIVE DIARRHEA:
Squirting, watery diarrhea from the rectum.
PROSTAGLANDINS:
A group of fatty acid-derived compounds that are important as regulators of a number of physiological processes involving allergic reactions, contraction of smooth muscle, dilation of blood vessels, blood clotting, and others.
PROSTATE GLAND:
Gland in male mammals that surrounds the urethra where it joins the bladder and is important in the production of seminal fluid.
PROSTATITIS:
Inflammation of the prostate gland.
PROTEIN-LOSING ENTEROPATHY:
Syndrome occurring in adult horses, characterized by weight loss in the face of a ravenous appetite; the cause is unknown but the result is a “leaky” intestine that does not absorb nutrients properly.
PROTEINS:
Molecules, composed of amino acids, that make up many of the structural components of the body and that are needed to maintain all normal body functions.
PROTEINURIA:
Excessive loss of protein in the urine.
PROTEOLYTIC:
Capable of breaking down protein.
PROTOZOA:
Simple organisms that are usually composed of a single cell; most are free-living but some are capable of producing disease in animals or humans.
PROXIMATE ANALYSIS:
A measure of the nutrient content of a diet, including the maximum moisture, maximum fiber, minimum crude protein, and minimum crude fat content.
PRURITUS:
Itchiness.
PSEUDOHYPERPARATHYROIDISM:
Disorder characterized by elevated levels of blood calcium resulting from production of a parathyroid hormonelike substance by a tumor.
PTYALISM:
Excessive drooling; hypersalivation.
PULMONARY:
Pertaining to the lungs.
PULMONARY EDEMA:
Noninflammatory buildup of fluid in the tissues and air spaces within the lungs.
PULMONARY EMBOLISM:
A detached clot from elsewhere in the body occluding a blood vessel within the lungs.
PULMONIC STENOSIS:
Congenital heart defect characterized by a narrowing (stenosis) of the connection between the right ventricle and the pulmonary artery.
PULMONIC VALVE:
The semilunar valve on the right side of the heart; also called the pulmonic semilunar outflow valve.
PULP:
The blood vessels, nerves, lymphatic channels, and cells that line the pulp chamber or root canal of each tooth.
PUNNETT SQUARE:
Checkerboard diagram for delineating possible outcomes of mating two individuals of defined genotype.
PUPIL:
The central opening of the iris, through which light penetrates into the inner reaches of the eye.
PURPURA HEMORRHAGICA:
Immunologically mediated condition characterized by swelling of the limbs and widespread skin hemorrhages, varying in severity from a mild transient reaction to a severe fatal condition; associated with a number of different inciting factors, occasionally streptococcal infections.
PURULENT:
Pus-forming.
PUS:
Fluid produced by an inflammatory process, containing many white blood cells.
PUSTULE:
A skin vesicle containing pus.
PUTREFACTIVE:
Pertaining to the normal decomposition of organic matter by microorganisms.
PYELONEPHRITIS:
Any infection of the kidney involving as well the renal pelvis.
PYLORIC SPHINCTER:
Sphincter located between the stomach and duodenum.
PYLORUS:
The terminal portion of the stomach, connecting it with the duodenum (first part of the small intestine).
PYODERMA:
General term for any skin disease in which pus is formed.
PYOMETRA:
Accumulation of pus within the uterus, resulting usually from a severe bacterial infection.
PYOMETRITIS:
Purulent inflammation of the uterus.
PYOTHORAX:
Accumulation of pus within the chest; also called thoracic empyema.
PYRROLIZIDINE ALKALOIDS:
Plant toxins that produce a very specific type of liver damage; the most common cause of chronic liver failure in horses in the western United States
QUADRIPARESIS:
Partial paralysis in all four limbs.
QUADRUPED:
An animal such as the horse that walks on all four limbs.
QUEENSLAND ITCH:
Commonly encountered skin disease of horses, caused by an allergic reaction to the bites of midges belonging to the genus Culicoides; also called sweet itch.
QUIDD:
To drop partially chewed feed material from the mouth.
QUITTOR:
Chronic inflammatory process of the collateral cartilage of the coffin bone.
RABIES:
Inevitably fatal viral disease, primarily of bats and carnivores, characterized by neurologic dysfunction; caused by a rhabdovirus.
RADIOGRAPH:
An X ray film.
RADIOGRAPHY:
The use of X rays or gamma rays to view the internal structures of the body.
RADIOISOTOPES:
Radioactive elements.
RADIOTHERAPY:
Radiation therapy.
RAIN-SCALD:
Common term for dermatophilosis.
RECESSIVE GENE:
A gene that can be expressed only when both members of a chromosome pair contain the same allele for a given characteristic (i.e., the same allele must be inherited from both the dam and the sire).
RECOMBINATION:
Genetic exchange among chromosomes, producing new combinations of genes.
RECTAL-VAGINAL FISTULA:
A tear from the top of the vestibule (entrance to the vagina) to the floor of the rectum.
RECTUM:
Lowermost portion of the large intestine, immediately adjacent to the anus.
RECUMBENCY:
Inability to stand.
RECUMBENT:
Lying down.
RECURRENT UVEITIS:
Periodic ophthalmia.
REDIA:
Larval stage of flukes arising from the sporocyst stage.
REDUCTION:
The setting of a bone fracture.
REFLEX:
In general, muscle movement orchestrated by the nervous system in response to a stimulus and without conscious (voluntary) control; an example is the knee-jerk reflex.
REFLUX:
Backward flow.
REFRACTIVE:
Light-bending.
REFRACTOMETER:
Small hand-held device that can be used for determining how concentrated or dilute a urine sample is (a measurement referred to as urine specific gravity).
REGURGITATION:
Involuntary return of undigested food to the mouth after swallowing; differs from vomiting in that it is a passive process (i.e., unaccompanied by the reflex, propulsive movements characteristic of vomiting).
RENAL:
Pertaining to the kidneys.
RENAL PELVIS:
“Collecting funnel” deep within each kidney into which the kidney tubules drain filtrate.
RESERVOIR HOST:
An animal from which infection may be passed to domesticated stock or to human beings.
RESORPTION:
Biochemical dissolution or loss of tissue.
RESPIRATION:
Breathing.
RETCHING:
Abdominal contractions in preparation for vomiting.
RETICULATED LEUKOTRICHIA:
A form of leukotrichia seen primarily in Quarter Horses.
RETINA:
The light-sensitive layer of cells at the back of the eye.
RETINITIS:
Inflammation of the retina.
RETROGRADE:
Backward.
RHABDOMYOMA:
A benign tumor of striated muscle cells.
RHABDOMYOSARCOMA:
A malignant tumor of striated muscle cells.
RHINITIS:
Inflammation of the nasal passages.
RHINOPNEUMONITIS:
Respiratory condition of horses caused by equine herpesvirus.
RHINOSCOPY:
Visual examination of the nasal passages, using an endoscope, otoscope, or other instrument.
RHINOSPORIDIOSIS:
An uncommon disease caused by an as yet poorly characterized fungus, Rhinosporidium seeberi; it is a chronic localized infection characterized by the formation of polyps (fleshy masses protruding from the surface of a mucous membrane) in the nasal passages.
RHYTHMIC SEGMENTATION:
Rhythmic muscular movements of the intestinal tract that serve to delay the passage of intestinal contents until digestion and absorption have been completed.
RIBONUCLEIC ACID (RNA):
A nucleic acid occurring in all cells and involved in cell division, gene expression, and protein synthesis; also serves as the genetic material for some viruses.
RICKETTSIAE (SINGULAR: RICKETTSIA):
Specialized bacteria that multiply only within host cells and that are usually transmitted to animals or human beings by lice, ticks, fleas, or mites; examples include Ehrlichia risticii, the cause of Potomac horse fever (equine monocytic ehrlichiosis), and Ehrlichia equi, the cause of equine granulocytic ehrlichiosis.
RINGBONE:
Disorder characterized by new bone growth adjacent to either the pastern or coffin joints; caused by tearing of the collateral ligaments stabilizing the joint. High ringbone describes bone growth around the pastern joint, while low ringbone describes bone growth around the coffin joint.
RINGWORM:
A common skin infection caused by ringworm fungi (dermatophytes), which invade the outer, superficial layers of the skin, hair, and nails; also called dermatophytosis.
RNA:
See ribonucleic acid.
ROARING:
Common name for laryngeal hemiplegia.
RODS:
Photoreceptor cells in the retina of the eye that are responsible for night vision and detection of motion.
ROOT:
The portion of a tooth that lies below the gumline.
ROOT CANAL:
The chamber within each tooth that contains nerves, blood vessels, and lymphatic channels; also known as the pulp chamber.
SACROILIAC JOINT:
Joint where the pelvis connects with the spine.
SACRUM:
Bone formed by the fusion of the sacral vertebrae, at the lower end of the spinal column.
SALINE:
A physiologically balanced salt solution; physiological sodium chloride solution.
SALMONELLOSIS:
A primarily diarrheal disease caused by members of the bacterial genus Salmonella.
SAN JOAQUIN VALLEY FEVER:
Coccidioidomycosis (“valley fever”).
SAND COLIC:
Colic resulting when horses are fed on the ground in areas where the soil is sandy, or when they develop the vice of eating soil.
SARCOID:
A skin tumor unique to horses, mules, and donkeys; lesions usually appear as small growths on a stalk or as large, broad-based masses.
SARCOLEMMA:
The outer membrane surrounding every skeletal muscle fiber.
SARCOMA:
General term for malignant tumors of connective-tissue cells (those cells within an organ or structure that bind it together and support it).
SATIETY:
Appeasement of the appetite; a feeling of sufficiency or satisfaction with regard to food intake.
SCAPULA:
Shoulder-blade.
SCHIZOGONY:
A form of asexual reproduction seen in certain protozoa, in which the nucleus of the organism divides several times before the remainder of the cell divides; also called multiple fission.
SCHIZONT:
A developmental stage of certain protozoa, specifically, a dividing cell undergoing schizogony; also called a meront.
SCHWANN CELLS:
Large cells that are wrapped around certain nerve axons to form a myelin sheath, which serves to facilitate the conduction of nerve impulses along the axon.
SCLERA:
The white outer covering of the eyeball, continuous with the cornea.
SCLEROTIC:
Hardened.
SCOLEX:
The “head” of a tapeworm parasite, armed with hooks or suckers and used for attachment and locomotion.
SCOTOMA:
A localized, disease-caused “blind spot” in the retina.
SCOURS:
Diarrhea.
SCROTUM:
Dependent pouch of skin containing the testicles.
SCUTUM:
The hard “shield” present on the back of a hard tick.
SEBACEOUS GLANDS:
Minute skin glands, many of which are attached to hair follicles; they secrete sebum, an oily secretion that lubricates and protects the skin.
SEBORRHEA:
General term used to describe clinical signs of excessive scaling, crusting, and greasiness of the skin.
SEBUM:
The oily secretion of the sebaceous glands, containing fats, bacteria, and dead skin cells; it lubricates and protects the skin surface.
SECONDARY LYMPHOID ORGANS:
Organs in which antigens are trapped and destroyed by immune-system cells; they include the lymph nodes, spleen, and portions of the bone marrow and the mucosal-associated lymphoid tissue (MALT).
SEIZURES:
Relatively brief episodes of neurologic derangement caused by abnormal bursts of electrical activity within the brain; also called convulsions or fits.
SELECTIVE IGM DEFICIENCY:
Immunologic disorder characterized by subnormal levels of circulating IgM; seen primarily in the Arabian and Quarter Horse breeds.
SELF-LIMITING:
Said of disease, with reference to any illness that will run its (usually benign) course without the need for treatment.
SEMEN:
Thick milky fluid from the male containing the male reproductive cells or spermatozoa (sperm).
SEMICIRCULAR CANALS:
Structures in the inner ear that are concerned with the sensation of balance.
SEMILUNAR VALVES:
The heart valves that separate each ventricle from the great artery with which it is connected (either aorta or pulmonary artery). The semilunar valve on the right side of the heart is known as the pulmonic valve, and the corresponding valve on the left side is called the aortic valve.
SEMINAL VESICLES:
Pouches attached to the urinary bladder.
SEMINIFEROUS TUBULES:
Small channels within the testes wherein the spermatozoa (sperm) develop.
SEMINOMA:
The most common type of testicular tumor in the horse.
SEPTIC ARTHRITIS:
Inflammation of the joints caused by an infectious agent, usually bacterial.
SEPTIC SHOCK:
Shock caused by invasion of the body by bacteria that produce substances injurious to cells such that the cells can no longer utilize oxygen.
SEPTICEMIA:
The presence of bacteria in the blood circulation, accompanied by related clinical signs of disease.
SEPTUM (PLURAL: SEPTA):
A dividing wall, such as that dividing the right and left sides of the heart or the right and left nasal cavities.
SEQUESTRUM (PLURAL: SEQUESTRA):
A fragment of dead bone that has broken off from the underlying normal bone tissue.
SEROLOGY:
The use of specialized diagnostic tests for the detection of antigens and antibodies in serum.
SEROTYPE:
Variant of an infectious agent based on immunological testing.
SEROVAR:
Variant or subspecies of leptospire.
SERTOLI CELLS:
Cells within the testicular tubules that are important for nuture and development of spermatozoa (sperm).
SERUM:
Blood plasma minus the clotting factor fibrinogen; the clear liquid that remains after the blood clots, containing many important blood proteins including antibodies (immunoglobulins).
SERUM ALKALINE PHOSPHATASE (SAP):
An enzyme present in the blood that is produced in many body tissues and is of greatest diagnostic significance in diseases of the bone and liver.
SERUM HEPATITIS:
An acute form of liver failure in adult horses associated in most cases with the injection of some biological product of equine origin, usually tetanus antitoxin; also called Theiler’s disease.
SESAMOID BONE:
Any small, nodular bone (such as the kneecap) that is located within the tendon of a muscle or the capsule of a joint.
SESAMOIDITIS:
Inflammation of the proximal sesamoid bones, sometimes involving the suspensory ligament and distal sesamoidian ligaments as well.
SEVERE COMBINED IMMUNE DEFICIENCY (SCID, CID):
Lethal, inherited disease of Arabian foals, characterized by an absence of T- and B-lymphocytes. Approximately 2% of Arabian foals are born with this condition.
SEX-LINKED DISEASES:
Genetic diseases of males caused by defective genes located on the X chromosome; also called X-linked diseases.
SEXUAL DIMORPHISM:
Size differences between the sexes, as seen with certain parasites.
SHAKER FOAL SYNDROME:
Form of botulism in 2- to 8-week-old foals that occurs following ingestion of Clostridium botulinum spores and their transformation into mature, toxin-producing bacterial forms in the intestinal tract.
SHAPING:
In training, the gradual refining or improvement of a task or movement.
SHEARED HEELS:
Breakdown of the tissue between the bulbs of the heel, caused by the hoof wall’s being out of balance.
SHEATH:
Fold of skin enclosing the penis; prepuce.
SHOCK:
Failure of the blood vascular system to provide adequate circulation to the vital organs; circulatory collapse.
SHOE BOIL:
Common term for olecranon bursitis.
SIALOLITH:
Small stony concretion that forms within a duct draining a salivary gland, potentially resulting in blockage of the duct.
SIDEBONES:
Term describing ossification (bone formation) of the collateral cartilages of the foot; usually occurs in the forefeet of horses with poor conformation.
SIGN:
A characteristic of a disease; “signs” are seen by observation, while “symptoms” are characteristics reported by the patient; thus, animals exhibit signs of disease, while human beings report symptoms.
SINOATRIAL (SA) NODE:
A collection of specialized cardiac muscle fibers found at the junction of the right atrium and the vena cava; the heart’s natural pacemaker, generating the electrical discharges that stimulate the beating and pumping of the heart.
SINUS EMPYEMA:
Formation of pus in the paranasal sinuses; the underlying cause in many cases is dental disease.
SINUSITIS:
Inflammation of a sinus.
SKELETAL MUSCLE:
The type of muscle making up most of the muscles of movement attached to the skeleton; also known as striated muscle.
SKEWBALD:
White and any color other than black (horse coloration).
SLEEPING SICKNESS:
Common term for the depression and somnolence characteristic of equine viral encephalomyelitis.
SMEGMA:
Thick, oily or cheesy secretion that collects beneath the sheath of the penis.
SMOOTH MOUTH:
“Smoothing” of the tooth surfaces seen in very old horses.
SMOOTH MUSCLE:
The type of muscle found in the walls of blood vessels and the major internal organs.
SOFT PALATE:
At the rear of the mouth, the soft, fleshy posterior partition separating the nasal and oral cavities.
SOFT-TISSUE ORBIT:
The nonbony structures (muscles, nerves, blood vessels) that lie within the bony orbit.
SOLUBLE FIBERS:
Dietary fibers as found in fruits, oat bran, and psyllium (the chief component of commercial stool softeners such as “Metamucil”); they attract water and form a gel, are highly fermentable (able to be digested by bacteria) in the large intestine, and have been shown in people to slow emptying of the stomach and to inhibit the absorption of cholesterol.
SOMATOMEDINS:
Small proteins produced mainly in the liver that exert an anabolic effect on the body, resulting in proliferation of bone, cartilage, and soft tissues, and enlargement of body organs; also known as insulinlike growth factors.
SOW MOUTH:
Dental malformation consisting of an underextended upper jaw.
SPASMODIC COLIC:
Colic characterized by increased numbers of bowel movements and episodes of pain following sudden changes in environmental temperature, diet, or activity level.
SPECIES:
One of the major classifying categories of taxonomy, representing divisions of a genus, and sometimes further classified into subspecies.
SPECIFIC GRAVITY:
A measurement of the concentration of urine in a urine sample; determined by using a small hand-held device called a refractomer.
SPERMATIC CORD:
Combined structure extending from the groin area to the testes, through which run the vas deferens and a number of vessels and nerves.
SPERMATOGENESIS:
The process whereby sperm cells within the testes of the stallion undergo cell divisions and cellular changes that result in the produce of mature spermatozoa (sperm).
SPERMATOZOA (SINGULAR: SPERMATOZOON):
The mature reproductive cells of the male; produced by the testes, their role is to fertilize the female egg (ovum).
SPHERULE:
The parasitic, noninfectious stage of the fungus Coccidioides immitis, formed during the organism’s growth phase in host tissue.
SPHINCTER:
Circular band or ring of muscle that serves to open or close a tube or orifice; analogous to a valve.
SPINAL NERVES:
Nerves arising from the spinal cord that form nerves of the peripheral nervous system.
SPIROCHETES:
Filamentous, spiral-shaped bacteria, such as the leptospires and Borrelia.
SPLEEN:
Large abdominal organ that removes senescent (aged) red blood cells and foreign material from the bloodstream; an important component of the immune system.
SPLENECTOMY:
Surgical removal of the spleen.
SPLINT BONES:
The second and fourth metacarpal bones of the forefoot, attached to the cannon bone by interosseous ligaments.
SPLINTING:
Tightening of the muscles in an area in order to avoid pain associated with muscle movement.
SPLINTS:
Inflammation of the interosseous ligament that attaches the splint bones to the cannon bone.
SPORE:
Highly resistant, thick-walled “resting stage” formed by certain bacteria, to ensure their survival during periods of unfavorable environmental conditions; it germinates quickly once favorable conditions have been restored to produce a new generation of bacteria. Also, a general term referring to the reproductive cells of certain microorganisms, particularly fungi and protozoa.
SPOROCYST:
Larval stage of flukes that arises from the free-swimming miracidium stage.
SPOROTRICHOSIS:
An uncommon chronic, pus-forming infection caused by the dimorphic fungus Sporothrix schenckii.
SPOROZOITES:
In certain protozoa, the daughter cells resulting from division of a fertilized cell (zygote).
SPRAIN:
Joint injury involving damage to one or more ligaments, but without actual ligament rupture.
SQUAMOUS CELL CARCINOMA:
A malignant skin tumor of cells within the squamous cell layer of the epidermis.
SQUAMOUS CELL LAYER:
A layer of cells within the epidermis, the outermost layer of the skin; also known as the prickle cell layer, it lies above the basal cell layer and below the granular cell layer.
STALL-WALKING:
A stable vice characterized by constant circling, the horse’s feet describing a roughly circular path through the bedding material on the floor of the stall.
STANDING HEAT:
Behavioral estrus; the full behavioral signs of estrus.
STENOSIS:
A constriction or narrowing of a vessel or duct.
STEP MOUTH:
Abnormality of older horses characterized by a wavelike or stair-step configuration of the premolars and molars from front to back; also called wave mouth.
STEREOPSIS:
Depth perception.
STERNAL:
Resting on the breastbone or sternum.
STERNUM:
Breastbone.
STEROID HORMONES:
Hormones manufactured by the body from cholesterol and protein.
STERTOR:
Noisy breathing.
STIFLE JOINT:
Joint where the femur joins the tibia; equivalent to the human knee joint.
STOMATITIS:
Inflammation of the lining of the mouth.
STRANGLES:
Extremely important, highly contagious bacterial disease of young horses caused by Streptococcus equi; characterized by inflammation of the pharyngeal mucous membranes, with swelling, inflammation, and abscess formation in the associated lymph nodes; also called distemper.
STRANGULATION:
Constriction resulting in impairment of the blood supply.
STREPTOTHRICOSIS:
Dermatophilosis.
STRIATED MUSCLE:
Skeletal muscle.
STRICTURE:
Narrowing of the diameter of a hollow tube, usually the result of contraction caused by local tissue damage.
STRIDOR:
Loud, strained, high-pitched noise on inhalation.
STRINGHALT:
Condition in which the horse involuntarily hyperflexes the hock as it walks; the cause is unknown.
STROBILA:
The body of a tapeworm parasite, comparised of a chain of segments called proglottids.
STRONGYLES:
Nematode parasites of horses; come in two varieties, large and small strongyles
SUBCUTANEOUS (SC):
Beneath the skin; a route of injection.
SUBCUTANEOUS EDEMA:
Accumulation of fluid beneath the skin.
SUBCUTIS:
The skin layer lying beneath the dermis, and composed of fat cells and strands of collagenous connective tissue; also called hypodermis.
SUBFERTILITY:
A state of being less than normally fertile, but not infertile.
SUBGINGIVAL:
Below the gumline.
SUBINVOLUTION:
Partial involution (return to normal size) of an organ, as of the uterus following delivery of the fetus.
SUBLUXATION:
Partial dislocation of a joint; also, a slight alteration in the position of the lens of the eye.
SUBMANDIBULAR:
Beneath the lower jaw.
SUCROSE:
Table sugar.
SULFUR GRANULES:
Yellowish clumps of bacteria mixed with dead and dying cells, commonly observed in the pus draining from lesions of actinomycosis.
SUMMER SORES:
Common term for cutaneous habronemiasis.
SUPPURATIVE:
Producing pus (said of bacterial infections).
SURFACTANT:
A soaplike substance produced by specialized cells lining the alveoli of the lungs; responsible for decreasing the pressure (surface tension) within the alveoli and preventing them from collapsing during normal respiratory movements.
SUTURE:
A surgical stitch.
SWAMP FEVER:
Equine infectious anemia.
SWEENY:
Atrophy of the supraspinatus and infraspinatus muscles, located over the scapula (shoulder-blade); usually caused by damage to the nerve supply to these muscles.
SWEET ITCH:
Queensland itch.
SYMPTOMATIC THERAPY:
Therapy aimed at alleviating the signs or symptoms of a disease rather than treating its underlying cause.
SYNAPTIC CLEFT:
The space between an axon terminal and the myofiber it supplies, and across which the nerve impulse is transmitted by means of “messenger molecules” such as acetylcholine.
SYNGAMY:
Alternative term for gametogamy.
SYNOVIAL FLUID:
Joint fluid, the material that lubricates the joint surfaces.
SYNOVIAL MEMBRANE:
The lining membrane of a joint.
SYNOVITIS:
Inflammation of the lining membrane of a joint.
SYSTEMIC:
Throughout the body; pertaining to the body as a whole.
SYSTEMIC LUPUS ERYTHEMATOSUS (SLE):
A rare, chronic, multisystemic autoimmune disorder, characterized by the production of autoantibodies to DNA and normal cellular constituents.
SYSTOLE:
The contraction/ejection phase of the heartbeat.
SYSTOLIC BLOOD PRESSURE:
The pressure that occurs when the heart contracts and pushes blood into the arterial system.
T LYMPHOCYTES (T CELLS):
Specialized lymphocytes that mature within the thymus; two important types are cytotoxic T cells and helper T cells.
TACHYCARDIA:
Abnormally fast heart rate.
TACHYPNEA:
Abnormally rapid breathing.
TACHYZOITES:
Actively dividing form of the parasite Toxoplasma gondii found in the tissues of an infected animal.
TAIL-CHEWING:
A stable vice exhibited primarily by yearlings and two-year-olds.
TAPETUM:
The reflective layer in the upper half of the back of the eye.
TAXONOMY:
The classification of organisms into different categories on the basis of their individual physical and biochemical relationships to each other.
TELOGEN:
The phase of hair follicle activity during which the follicle is resting and not producing new hair.
TEMPORAL REGION:
Area of the head in front of the ears and lateral to the forehead.
TENDINITIS:
Inflammation of a tendon or tendon muscle attachment; also spelled tendonitis.
TENDON:
Fibrous tissue that attaches muscle to bone.
TENOSYNOVITIS:
Inflammation of the lining membrane that surrounds the tendon sheath.
TENOTOMY:
Surgical cutting of a tendon.
TERATOGEN:
Any compound or agent that disrupts normal development in utero, producing defects in the developing embryo.
TERATOLOGY:
The study of abnormal development and congenital malformations.
TERATOMA:
Ovarian tumor characterized by the formation of cysts as well as a bizarre combination of different embryonic tissues such as bone, cartilage, teeth, and hair.
TEST CROSS:
A mating between a homozygous recessive and an animal with the phenotype of the dominant allele.
TESTES, TESTICLES:
Paired reproductive organs of the male wherein the spermatozoa (sperm) are produced.
TESTOSTERONE:
The principal male sex hormone, produced in the testes.
TETANOSPASMIN:
The neurotoxin produced in tetanus.
TETANUS:
Acute, often fatal disease caused by a neurotoxin from the bacterium Clostridium tetani, and characterized by violent muscle spasms and contractions, hyperreflexive responses, and “lockjaw” (trismus); horses are highly sensitive to the action of tetanus neurotoxin.
TETANY:
Seizurelike tremors caused most often by a decrease in circulating calcium levels.
TETRALOGY OF FALLOT:
Congenital heart defect characterized by the presence of a ventricular septal defect (VSD) and severe pulmonic stenosis, together with an abnormally positioned aorta and thickening of the right ventricle.
TETRAPLEGIA:
Paralysis of all four limbs.
THALAMUS:
Portion of the brain that serves as a relay center for sensory information coming from the rest of the body, and for nerve impulses concerned with balance and coordination arising from the cerebellum.
THEILER’S DISEASE:
Alternative name for serum hepatitis.
THERIOGENOLOGY:
Study of the physiology and pathology of animal reproduction.
THERMOCAUTERY:
Destruction of tissue using a hot point or instrument.
THORACIC:
Pertaining to the chest.
THORACOCENTESIS:
Procedure in which a sterile hypodermic needle is inserted into the chest cavity in order to remove accumulated air or fluid, or to obtain a sample of fluid or lung tissue for examination.
THORACOLUMBAR:
Pertaining to the upper trunk and back.
THOROUGHPIN:
Stress on the deep digital flexor tendon, with puffiness in the web of the hock.
THROATLATCH:
Area of the throat under which the strap of a bridle or halter passes.
THROMBOCYTOPENIA:
Abnormally decreased numbers of circulating blood platelets.
THROMBOEMBOLISM:
Obstruction of a blood vessel by a clot originating at another site.
THROMBOPHLEBITIS:
Inflammation of a vein, accompanied by the formation of a blood clot.
THROMBOPLASTIN:
A protein essential for blood clotting.
THROMBOSIS:
Formation of a blood clot (thrombus) that results in obstruction of a blood vessel at the site of clot formation; contrasts with embolism, which is a blood-borne clot that lodges at a site distant from its site of formation.
THROMBUS:
A blood clot causing obstruction of a blood vessel at the site of clot formation.
THRUSH:
Degenerative condition of the frog of the foot, characterized by infection and blackening of the affected area; usually occurs in horses housed under unsanitary conditions.
THYMUS:
Lymphoid organ located in the chest that produces hormones (thymopoietin, thymosin) and that regulates the maturation process of specialized lymphocytes known as T cells.
THYROID GLAND:
Endocrine gland located on either side of the trachea that produces hormones (thyroxine, triiodothyronine) important in regulating the body’s metabolic rate.
THYROID HORMONE:
Collective name for the two major hormones produced by the thyroid gland, thyroxine (T4) and triiodothyronine (T3).
THYROIDECTOMY:
Removal of all or part of the thyroid gland.
THYROID-STIMULATING HORMONE (TSH):
Hormone elaborated by the pituitary gland that stimulates the thyroid gland to produce the hormones thyroxine (T4) and triiodothyronine (T3).
THYROXINE (T4):
One of two important iodine-containing hormones secreted by the thyroid gland that assist in regulating the cellular metabolic rate of the body.
TITER:
A quantitative measure of the concentration of an antibody or antigen in blood serum; determined in principle by making serial dilutions of serum and identifying the highest dilution at which the antibody or antigen can still be detected.
TOBIANO:
Dominantly inherited equine coat-color pattern, expressed as a white base coat with colored patches on the body. The legs are usually white, and white normally crosses the back. The colored areas are regular, usually oval or round. The head is colored as are the flanks.
TOCOPHEROLS:
General term for vitamin E.
TOLERANCE:
The normal state whereby the immune system remains nonreactive or “tolerant” to the body’s own cells.
TORSION:
A twisting.
TOTAL DIGESTIBLE NUTRIENTS (TDN):
For a feed, the sum of the digestible carbohydrate, protein, fat, and fiber; also called digestible energy (DE).
TOVERO:
Equine coat-color pattern with characteristics of both tobiano and overo.
TOXEMIA:
Presence of toxins in the blood, accompanied by related signs of disease.
TOXOPLASMOSIS:
A protozoan disease caused by Toxoplasma gondii.
TRACE MINERALS:
Minerals that are required in the diet only in very minute amounts; for horses these usually include copper, iodine, iron, manganese, selenium, and zinc.
TRACHEA:
Cartilage-lined tubular airway that descends from the larynx into the chest and branches at its lower end into two bronchi that enter the lungs; it conducts air between the upper nasal passages and the lungs; colloquially known as the windpipe.
TRACHEITIS:
Inflammation of the trachea.
TRACHEOSTOMY:
Surgically created opening through the skin into the trachea, to allow for insertion of a tube for breathing and to clear airway obstructions.
TRANSMAMMARY:
Through the milk or colostrum.
TRANSPLACENTAL(LY):
By way of the placenta; across the placenta.
TRANSPORT HOST:
An animal in which part of the immature phase of a parasite’s life cycle is spent, but no development occurs.
TRANSTRACHEAL WASH:
Flushing of material from the trachea and bronchi for diagnostic purposes, by needle puncture and aspiration through the skin and tracheal wall.
TREMATODES:
Flukes.
TRICHIASIS:
Condition wherein facial hair or eyelashes arising from normal sites are misdirected and contact the cornea or conjunctiva.
TRICHINOSIS:
Serious, occasionally fatal food-borne disease of humans caused by a parasitic worm, Trichinella spiralis, whose larval forms are found in muscle tissue. When the (raw or undercooked) muscle is eaten, the larvae are liberated and mature in the small intestine, where the adults reproduce and produce offspring.
TRICUSPID VALVE:
The atrioventricular valve on the right side of the heart.
TRIGLYCERIDES:
A component of fat, consisting of fatty acids linked to glycerol.
TRIIODOTHYRONINE (T3):
An important iodine-containing hormone secreted by the thyroid gland that assists in regulating the cellular metabolic rate of the body; much more powerful than its companion hormone thyroxine, it is considered to be the active form of thyroid hormone in tissue.
TRISMUS:
“Lockjaw,” caused by spasm of the chewing muscles; seen in tetanus..
TROCHANTERIC BURSITIS:
Inflammation of the bursa that lies beneath the tendon of the middle gluteal muscle as it passes over the point of the hip.
TROPHOZOITES:
Motile feeding forms of the parasite Giardia; they multiply in the small intestine by means of binary fission.
TRUNCUS ARTERIOSUS:
Congenital heart defect consisting of a ventricular septal defect (VSD) and a single large arterial trunk exiting both ventricles.
TUBERCULOSIS:
An ancient disease of humans and animals, caused by bacteria belonging to the genus Mycobacterium. Most infections in horses are caused by Mycobacterium bovis and are characterized by fever, respiratory difficulty, inappetence, weight loss, and lymph node enlargement.
TUMOR:
A large nodule, or obvious cancerous mass.
TURGOR:
Skin elasticity.
TURNER’S SYNDROME:
The most common chromosomal abnormality of mares, characterized by a missing X chromosome; also called 63,X gonadal dysgenesis.
TYING-UP:
A mild form of azoturia.
TYMPANIC MEMBRANE:
Eardrum.
TYMPANY:
Distension.
TYZZER’S DISEASE:
An extremely rare and highly fatal liver disease of foals caused by a spore-forming bacterium, Bacillus piliformis.
ULCER, ULCERATION:
A severe sloughing of the surface of an organ or tissue, as a result of a toxic or inflammatory response at the site.
ULCERATIVE KERATITIS:
Inflammation of the cornea accompanied by corneal ulceration.
ULCERATIVE LYMPHANGITIS:
Uncommon condition affecting the lymphatic vessels; can be caused by either Corynebacterium pseudotuberculosis or Sporothrix schenckii, usually as the result of wound contamination. The lesions appear as nodules that develop most often on the hind legs below the hocks. The nodules eventually break down and ulcerate, releasing a thick greenish pus mixed with blood.
ULTRASONOGRAPHY:
Noninvasive diagnostic technique for visualizing the internal structures of the body by means of sound (echo) reflections; ultrasound.
ULTRASOUND:
Ultrasonography.
ULTRAVIOLET RADIATION:
High-energy radiation existing beyond the violet region of the electromagnetic spectrum; ultraviolet rays emitted by the sun are responsible for a number of effects on the skin, including tanning, burning, and activation of vitamin D.
UMBILICAL CORD:
Blood-vessel connection between the mare and the fetus.
UNICELLULAR:
Single-celled.
UNILATERAL:
Occurring on only one side.
UNILATERAL PAPULAR DERMATOSIS:
Poorly understood skin disease of Quarter Horses.
UNSOUNDNESS:
Any deviation in structure or function that interferes with a horse’s intended use or performance.
UNTHRIFTY:
Unkempt in appearance and failing to thrive.
URACHUS:
Structure that during fetal life transports the foal’s urine into the placental fluids; it normally closes off after birth.
UREA:
Nitrogen-containing compound generated by the breakdown of ingested proteins.
UREMIA:
Abnormally elevated levels of urea and other nitrogenous waste products in the blood.
URETER:
Membranous tube that transports urine from the kidney to the urinary bladder.
URETEROLITH:
Urinary stone lodged in the ureter.
URETHRA:
Membranous tube that transports urine from the urinary bladder to the exterior of the body.
URETHRAL DIVERTICULAR CONCRETION:
The accumulation of smegma into a solidified mass in the urethra, resulting in inflammation and obstruction; also called bean.
URETHRITIS:
Inflammation of the urethra.
URETHROLITH:
Urinary stone lodged in the urethra.
URINALYSIS (UA):
Panel of physicochemical tests carried out on urine, as an aid in the diagnosis of urinary-tract disorders.
URINARY CALCULUS (PLURAL: CALCULI):
General term for a stone lodged anywhere within the urinary tract; also known as a urolith.
URINE:
The fluid filtrate of the kidneys.
URINE SEDIMENT:
Urine solids obtained by centrifuging a urine sample.
UROLITH:
General term for a urinary stone.
UROLITHIASIS:
The formation of urinary stones; uncommon in horses.
UROPERITONEUM:
Accumulation of urine in the abdominal cavity.
UROSPERMIA:
Urination during ejaculation.
UROVAGINA:
Urine “pooling” in the vagina; also called vesicovaginal reflux.
URTICARIA (“HIVES”):
Acute, usually localized skin swelling caused by an increased permeability of capillaries, producing a net outflow of fluid into the tissue spaces; often a manifestation of an allergic process.
UTERINE HORNS:
Paired branchings of the uterus leading from the body of the uterus to the uterine tubes.
UTERINE INVERSION:
Protrusion of a portion of the uterus through the cervix; uterine prolapse.
UTERINE PROLAPSE:
Uterine inversion.
UTERINE TORSION:
Twisting of the uterus, which may occur late in pregnancy when the uterus is very enlarged.
UTERINE TUBES:
Paired fallopian tubes of the uterus wherein fertilization of the eggs with sperm occurs; also called oviducts.
UTERUS:
Organ in the female wherein the fertilized egg implants and develops through embryonic and fetal stages until birth; womb.
UVEA:
Cellular layer of the eye that contains blood vessels, the iris, ciliary body, and choroid.
UVEITIS:
Inflammation of the uvea of the eye.
VACUOLE:
Small, round to oval space or cavity within a cell.
VAGINA:
The genital canal of the mare, extending from the cervix of the uterus outward to the vulva.
VAGINITIS:
Inflammation of the vagina.
VAGINOSCOPIC:
By means of visual inspection of the vagina, using a speculum.
VALLEY FEVER:
Coccidioidomycosis.
VALVULAR DEGENERATION:
Heart disease wherein the leaflets or cusps comprising a heart valve curl back on themselves, allowing the valve to leak.
VAS DEFERENS:
Ducts that serve as the transport conduit for sperm from the testes to the urethra; also called ductus deferens.
VASCULAR:
Pertaining to blood vessels.
VASCULAR ENDOTHELIUM:
Cells lining the inner surface of blood vessels.
VASCULAR RING DEFECT:
Abnormal retention of embryonic blood vessels in the region of the aorta.
VASCULARIZATION:
The formation of blood vessels at a tissue site.
VASCULARIZED:
Supplied with blood vessels.
VASCULATURE:
The blood vessels,arteries, arterioles, capillaries, venules, and veins,that traverse the body.
VASCULITIS:
Inflammation of a blood vessel or vessels; also called angiitis.
VASECTOMY:
Sterilization of the male by severing the testicular tubules (vas deferens) without removing the testes.
VASODILATION:
Dilation (expansion in diameter) of a blood vessel.
VASOPRESSIN:
Alternative name for antidiuretic hormone (ADH).
VECTOR:
A term usually applied to insects, ticks, and mites that carry disease-causing microorganisms from an infected animal to a noninfected animal.
VEINS:
Large, thin-walled vessels that direct dexygenated blood from the tissues back to the heart.
VENIPUNCTURE:
Taking a blood sample from a vein.
VENOUS:
Pertaining to veins or venules.
VENTRAL:
In a direction toward the belly surface.
VENTRAL EDEMA:
Tissue swelling affecting the underside of the body.
VENTRICLES:
The two muscular, lower chambers of the heart, that are primarily responsible for pumping blood out of the heart; also, cavities in the brain within which is produced the cerebrospinal fluid.
VENTRICULAR AFTERLOAD:
The resistance to blood flow faced by the ventricles of the heart as they contract.
VENTRICULAR FIBRILLATION:
Rapid, repeated firing of ventricular muscle fibers without coordinated contraction of the muscle itself; can result in cardiac arrest and death.
VENTRICULAR PRELOAD:
The ability of the ventricles of the heart to fill adequately during the relaxation phase (diastole) of the heartbeat.
VENTRICULAR SEPTAL DEFECT (VSD):
Congenital abnormality in which a hole exists in the wall (septum) separating the left and right ventricles of the heart; the most commonly recognized congenital heart defect of horses.
VENTRICULAR TACHYCARDIA:
Abnormal condition wherein damaged or diseased heart muscle within a ventricle begins contracting on its own, which it normally does not do.
VENULES:
Small veins.
VERMINOUS PNEUMONIA:
Pneumonia caused by parasitic worms.
VERTEBRAE:
Blocklike bones that make up the spinal column and through which the spinal cord runs.
VESICLE:
A circumscribed elevation of the epidermis, filled with serum; blister.
VESICOVAGINAL REFLUX:
The retention of incompletely voided urine in the forward portion of the vagina, next to the cervix; also called urovagina.
VESICULAR:
Fluid-filled; causing blisters.
VESICULAR STOMATITIS:
Disease characterized by fever and the development of vesicles (blisters) and ulcerations of the mouth, tongue, coronary band, and teats; caused by a rhabdovirus.
VESTIBULAR:
Pertaining to the balance mechanism in the inner ear and brain.
VESTIBULE:
Outer portion of the vagina into which the urethra (the connecting tube from the urinary bladder) empties.
VILLI (SINGULAR: VILLUS):
Tiny hairlike projections lining the interior of the small intestine, that serve to increase greatly the surface area available for the absorption of nutrients.
VIREMIA:
Presence of virus in the bloodstream.
VIRILIZING:
Producing male characteristics.
VIROLOGY:
The study of viruses.
VIRULENCE:
Measure of the disease-causing capacity of an infectious disease agent.
VIRULENCE FACTOR:
Any factor that enhances the ability of an infectious disease agent to infect the host and damage tissue.
VIRUS ISOLATION:
Procedure of propagating a virus artificially in the laboratory; more specifically, the process of recovering a virus from a tissue or fluid sample of an infected animal or human being.
VIRUSES:
Minute, nonliving infectious disease agents composed primarily of protein and nucleic acid (either RNA or DNA), and characterized by the absence of independent metabolism and an inability to replicate outside susceptible host cells.
VISCERA (SINGULAR: VISCUS):
Any of the large interior organs of the body.
VISCERAL PLEURA:
Membrane covering the surface of the organs in the chest cavity.
VITAMIN:
General term for a number of substances required in very small quantities for the normal functioning of the body’s metabolic processes.
VITILIGO:
Uncommon, acquired disorder of pigmentation characterized by progressive, usually well-circumscribed, areas of pigment loss in the skin.
VITREOUS BODY:
Viscous fluid filling the posterior portion of the eyeball (behind the lens); also called simply vitreous.
VITREOUS CHAMBER:
The deepest chamber of the eye, behind the lens.
VOMITING:
The forceful ejection of contents of the stomach and upper small intestine through the mouth.
VOMITING CENTER:
Portion of the brain that initiates vomiting.
VOMITUS:
Vomited material.
VULVA:
The external genitalia of the female, representing the entrance to the vagina; composed of the external lips or folds (labia) and the clitoris.
WALKING DISEASE:
Older name for pyrrolizidine alkaloid intoxication.
WAVE MOUTH:
Abnormality of older horses characterized by a wavelike or stair-step configuration of the premolars and molars from front to back; also called step mouth.
WEAVING:
A stable vice characterized by a repetitive rocking motion made by rhythmically swinging the head and neck from side to side while transferring the weight back and forth from one foreleg to the other.
WHEAL:
A discrete, well-circumscribed, reddened skin swelling with a flat top and steep-walled margins, produced by edema in the dermis; often associated with allergic reactions, i.e., urticaria; also called a “hive.”
WHITE MUSCLE DISEASE:
Muscle abnormality resulting from inadequate intake of selenium or vitamin E.
WINDPUFFS:
Chronic swelling of the fetlock joint.
WIND-SUCKING:
A stable vice in which the horse flexes its neck while forcibly swallowing air; also, aspiration of air and debris into the vagina (pneumovagina).
WITHERS:
Ridge between the shoulder blades.
WOBBLER SYNDROME:
A common cause of incoordination in young horses, particularly Thoroughbreds; results from spinal cord compression caused by a narrowing of the vertebral canal, malalignment of neck vertebrae, or excessive growth of the surrounding soft tissue; also called wobbles.
WOLF TOOTH:
A vestigial first premolar tooth, sometimes present.
X-LINKED DISEASES:
Genetic diseases of males caused by defective genes located on the X chromosome; also called sex-linked diseases.
YELLOW STAR THISTLE POISONING:
Degenerative brain disease caused by ingestion of yellow star thistle (Centaurea solstitialis) or Russian knapweed (Centaurea repens).
ZONA PELLUCIDA:
Thick, transparent outer envelope or casing that surrounds an ovum (egg).
ZOONOSIS, ZOONOTIC DISEASE:
Any disease that can be spread between animals and human beings; examples include plague, rabies, salmonellosis, and ringworm.
ZOOSPORE:
The motile, infective stage of Dermatophilus congolensis, the cause of a skin disorder known as dermatophilosis.
ZYGOTE:
Fertilized ovum (egg).