Vet Terminology starting with H on - from H2 antagonist to Hypoxia

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H2 antagonist - A compound which binds (attaches) to the area on a cell at which histamine also binds. By binding at the same site, the antagonist blocks histamine from binding and prevents histamine from producing its effects, which include the production of stomach acid.

Half-life - The time required for the level of a substance in the body (e.g., a drug or toxin) to be reduced by half.

Head pressing - Pressing the head against a wall or other hard object.

Head Tilt - see Torticollis

Heart block - A condition in which the electrical impulses of the heart are not properly conducted from the atria (chambers which receive the blood) to the ventricles (chambers which pump the blood).

Heartworm - A species of parasitic worm (Dirofilaria immitis) that lives and reproduces in the chambers of the heart of an animal. Microscopic, immature worms (microfilariae) circulate in the blood and are taken in by mosquitoes that bite the animal. Microfilariae mature in the mouthparts of the mosquito and infect another susceptible animal bitten by the same mosquito.

Heinz body - A condition in which the red blood cells are destroyed and this results in anemia. The specific type of anemia is called 'Heinz body anemia' because the red cells develop an abnormality called a 'Heinz body' which can be seen under the microscope. This anemia can occur as a reaction to certain medications and also in cats who eat onions.

Hemangiosarcoma - A malignant tumor of the blood vessels, usually occurring in the skin, liver, spleen, right atrium of the heart, and muscle; also called angiosarcoma.

Hematocrit - PCV (Packed Cell Volume), hematocrit: A laboratory test to monitor relative number of red blood cells present in the blood. A blood sample is placed in a tiny glass tube and spun in a centrifuge. The cells are heavier than the plasma and are compacted at one end of the tube. After the tube is spun, it is examined and the packed cell volume is determined as the percentage of the red cellular portion relative to the total amount of blood in the tube (i.e. remainder being the plasma). The normal for dogs is 40-59 and cats is 29-50.

Hematology - The study of blood, its physiology and pathology.

Hematoma - A mass of blood within the tissues. Generally, the result of trauma to the blood vessels or abnormal blood c lotting.

Hematuria - A condition of blood in the urine.

Hemodialysis - A process used to remove waste products from the blood.

Hemoglobin - A protein inside of red blood cells, responsible for the binding and transport of oxygen to the body tissu es (Hb).

Hemolytic - Causing the red blood cells to break open.

Hemoptysis - Blood in the sputum.

Hemorrhage - To bleed excessively; may be the result of injury or blood clotting abnormalities.

Hemostat - A small surgical instrument used to clamp blood vessels to prevent bleeding.

Hepatic - Pertaining to the liver.

Hepatic fibrosis - Scarring of the liver

Hepatitis - An inflammation or infection of the liver.

Hepatomegaly - Enlargement of the liver.

Herbivore - Animal that eats primarily plants and vegetation.

Hernia - The protrusion of an organ through an abnormal opening.

High titer vaccine - A modified live vaccine that contains a higher number of virus particles than the 'average' vaccine. High titer vaccines can generally elicit an immune system response in young animals who have a maternal antibody level that would prevent them from responding to an 'average' vaccine.

Histamine H2 receptor antagonist - A compound which binds (attaches) to the area on a cell at which histamine also binds. By binding at the same site, the antagonist blocks histamine from binding and prevents histamine from producing its effects, which include the production of stomach acid.

Hob - A male ferret.

Hormone - Chemical substance produced by one part of the body which serves as a messenger to or regulator of the processes of another part of the body.

Host - The organism in or on which a parasite lives. For example, dogs and cats are hosts for fleas and roundworms.

Humoral immunity - The immunity that is the result of antibody production by B cells. Compare with 'cell-mediated immunity.'

Hybrid - An animal that has parents of two different species, for instance, a mule's mother is a horse and its father is a donkey.

Hydrocephalus - A condition of fluid accumulation in the ventricles (spaces) of the brain; the swelling generally creates pressure on the brain tissues and can cause severe damage if not treated properly.

Hyper - A prefix meaning abnormally high or excessive.

Hypercalcemia - An increased level of calcium in the blood.

Hyperesthesia - Abnormal sensitivity to touch, pain, or other sensory stimuli.

Hyperglycemia - Higher than normal blood glucose level.

Hyperkalemia - Increased level of potassium in the blood.

Hyperphosphatemia - Elevated blood phosphate levels.

Hyperpigmentation - An increased dark color in the skin caused by the pigment 'melanin.'

Hyperplasia - An increase of the number of cells within an organ.

Hyperplastic - Abnormal increase in the amount of tissue, e.g., a hyperplastic ear would have increased numbers of cells in the ear canal, sometimes to the point of closing off the ear canal. In prostatic hyperplasia, the prostate enlarges due to an increased number of normal, not cancerous, cells.

Hyperreactive - Producing an exaggerated, or greater than normal response to a stimulus.

Hypersensitive - A type of allergic condition in which the body overreacts to a certain agent such as a bee sting or medication.

Hypertension - Blood pressure above normal.

Hyperthermia - An increase in body temperature above normal.

Hyperthyroidism - A condition, more commonly seen in cats, in which the thyroid gland produces too much thyroid hormone. See article: Hyperthyroidism in Cats.

Hypertrophy - An increase in the size of a tissue or organ due to the enlargement of existing cells.

Hyperventilate - An increase in the rate and/or depth of respiration such that the body loses too much carbon dioxide.

Hyphema - refers to the presence of blood in the anterior chamber of the eye. The condition is usually due to blunt trauma of the eye, although it may occur following surgical procedures or even spontaneously as a result of other underlying disorders. The condition is often obvious to the casual observer as blood beneath the cornea obscuring the view of the iris (colored part of the eye).

Hypo - A prefix meaning abnormally low or deficient.

Hypoglycemia - Lower than normal blood glucose level.

Hypokalemia - Lower than normal level of potassium in the blood.

Hypoplasia - Inadequate or defective development of tissue.

Hypotension - Blood pressure below normal.

Hypothermia - A decrease in body temperature below normal.

Hypothyroidism - A condition, more common in dogs, in which the thyroid gland does not produce enough thyroid hormone.

Hypovitaminosis A - A condition in which the body suffers from a deficiency in Vitamin A.

Hypoxia - Low oxygen level in blood and tissues.