Horse Health Glossary

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.

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.

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