Glossary

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H 

Hair follicle - a tiny opening in the skin from which a hair grows

Hardening of the arteries - the common name for arteriosclerosis

Hashimoto's disease - a disease in which the body's immune system attacks cells of the thyroid gland, resulting in a decrease in thyroid hormones

HDL - see High-density lipoprotein

Heart attack - see Myocardial infarction

Heart block - a disorder of the heart caused by a blockage of the nerve impulses to the heart that regulate heartbeat; may lead to dizziness, fainting, or stroke

Heartburn - a burning sensation experienced in the center of the chest up to the throat; may be caused by overeating, eating spicy food, or drinking alcohol; recurrent heartburn may be caused by acid reflux

Heart failure - the inability of the heart to pump blood effectively

Heart rate - the rate at which the heart pumps blood, measured in the number of heartbeats per minute

Heart valve - the structure at each exit of the four chambers of the heart that allows blood to exit but not to flow back in

Hematemesis - vomiting of blood

Hematocrit - the percentage of total blood volume that consists of red blood cells, which is determined by laboratory testing; can be an indicator of disease or injury

Hematoma - an accumulation of blood from a broken blood vessel

Hematuria - blood in the urine, which can be caused by urinary tract disorders (such as cysts, tumor, or stones) or by an infection

Hemochromatosis - a genetic disorder in which too much iron is absorbed from food

Hemoglobin - the pigment in red blood cells that is responsible for carrying oxygen; hemoglobin bound to oxygen gives blood its red color

Hemoglobinuria - hemoglobin in the urine

Hemolysis - the breakdown of red blood cells in the spleen, which is normal but can cause jaundice and anemia when the red blood cells are broken down too quickly

Hemophilia - an inherited disorder in which a person's blood lacks a certain protein important in forming blood clots, leading to excessive bleeding

Hemorrhage - the medical term for bleeding

Hemorrhoid - a bulging vein either at the opening of the anus or just inside the anus, often caused by childbirth or straining during bowel movements

Hemospermia - blood in the semen

Hemostasis - the stopping of bleeding by the body's mechanisms

Hepatic - a term used to describe something that is related to the liver

Hepatitis - inflammation of the liver, which may be caused by a viral infection, poisons, or the use of alcohol or other drugs

Hepatitis A - a form of hepatitis caused by the hepatitis A virus, usually transmitted by contact with contaminated food or water

Hepatitis B - a form of hepatitis (generally more serious than hepatitis A) caused by the hepatitis B virus, which is transmitted through sexual contact or contact with infected blood or body fluids

Hepatitis C - a form of hepatitis caused by the hepatitis C virus, which is transmitted through sexual contact or contact with infected blood or body fluids

Hepatitis D - a form of hepatitis that only causes symptoms when the individual is already infected with hepatitis B

Hepatoma - a cancerous tumor of the liver

Hepatomegaly - enlargement of the liver

Hereditary - describes a genetic trait that is passed from parents to children

Hermaphroditism - a rare condition in which an individual is born with both male and female reproductive organs

Hernia - the bulging of an organ or tissue through a weakened area in the muscle wall

Herpes encephalitis - brain inflammation caused by a herpes simplex virus that has spread from another part of the body

Herpes simplex - infection by the herpes simplex virus, which causes blisterlike sores on the face, lips, mouth, or genitals; in rare cases, can also affect the eyes, fingers, or brain

Heterosexuality - being sexually attracted to members of the opposite sex

Hiatal hernia - a type of hernia in which the stomach bulges up into the chest cavity through an opening in the diaphragm

Hiccup - involuntary sudden contraction of the diaphragm along with the closing of the vocal cords, producing a "hiccup" sound

High-density lipoprotein - a type of protein found in the blood that removes cholesterol from tissues, protecting against heart disease

Hirsutism - excessive hair or hair growth in unusual places, especially in women

Histamine - a chemical in some cells of the body that is released during allergic reactions, causing inflammation; also causes production of acid in the stomach and narrowing of the airways

H1 (histamine) blocker - a drug that blocks the action of histamine; used to treat inflammation

H2 (histamine) blocker - a drug used in the treatment of peptic ulcers that blocks histamine from causing acid production in the stomach

HIV - see Human immunodeficiency virus

Hives - the common term for urticaria, an itchy, inflamed rash that results from an allergic reaction

Homeostasis - the body's coordinated maintenance of the stable, internal environment by regulating blood pressure, blood sugar, body temperature, etc

Homosexuality - being sexually attracted to members of the same sex

Hormonal implant - surgical insertion of a small object just under the skin that slowly releases a synthetic hormone for purposes such as birth control

Hormone - a chemical produced by a gland or tissue that is released into the bloodstream; controls body functions such as growth and sexual development

Hormone replacement therapy - the use of natural or artificial hormones to treat hormone deficiencies

Hot flash - a sudden, temporary feeling of heat and sometimes sweating; usually occurs as a result of low estrogen levels in women because of menopause or after a hysterectomy

HTLV - see Human T-cell lymphotrophic virus

Human immunodeficiency virus - a retrovirus that attacks helper T cells of the immune system and causes acquired immunodeficiency syndrome (AIDS); transmitted through sexual intercourse or contact with infected blood

Human T-cell lymphotrophic virus - a virus similar to HIV that affects the same helper T cells, but usually accompanies adult T-cell leukemia or T-cell lymphomas

Hydramnios - an excess of amniotic fluid in the uterus during pregnancy

Hydrocele - a painless swelling of the scrotum, caused by a collection of fluid around the testicle; commonly occurs in middle aged men

Hydrocephalus - excess cerebrospinal fluid within the brain; commonly referred to as "water on the brain"

Hydrocortisone - a corticosteroid drug that is used to treat inflammation and allergies

Hygiene - the practice, maintenance, and study of health; commonly refers to cleanliness

Hymen - a thin fold of membrane partly closing the opening of the vagina; usually torn during first sexual intercourse or insertion of a tampon

Hypercalcemia - a condition marked by abnormally high levels of calcium in the blood; can lead to disturbance of cell function in the nerves and muscles and, if not treated, can be fatal

Hypercholesterolemia - an abnormally high level of cholesterol in the blood, which can be the result of an inherited disorder or a diet that is high in fat

Hyperglycemia - a condition characterized by abnormally high levels of glucose in the blood, usually as a result of untreated or improperly controlled diabetes mellitus

Hyperlipidemia - a general term for a group of disorders in which lipid levels in the blood are abnormally high, including hypercholesterolemia

Hyperparathyroidism - overactivity of the parathyroid glands, which increases calcium levels in the blood (called hypercalcemia) and decreases calcium in bones (causing osteoporosis)

Hyperplasia - the enlargement of an organ or tissue

Hypersensitivity - an excessive response of the body's immune system to a foreign protein

Hypertension - abnormally high blood pressure, even when at rest

Hyperthermia - an abnormally high body temperature

Hyperthyroidism - overactivity of the thyroid gland, causing nervousness, weight loss, fatigue, and diarrhea

Hypertrophy - increase in the size of an organ due to an increase in the size of its cells

Hypochondriasis - an abnormal condition in which a person is overly concerned with health and believes that he or she is suffering from a major illness despite medical opinion to the contrary

Hypodermic needle - a thin, hollow needle attached to a syringe; used to inject a medication under the skin, into a vein, or into a muscle

Hypoglycemia - abnormally low levels of glucose in the blood

Hypoplasia - failure of a tissue or organ to develop normally

Hypotension - the medical term for abnormally low blood pressure, which results in reduced blood flow to the brain, causing dizziness and fainting

Hypothermia - an abnormally low body temperature

Hypothyroidism - underactivity of the thyroid gland, causing tiredness, cramps, a slowed heart rate, and possibly weight gain

Hypoxemia - a reduced level of oxygen in the blood

Hypoxia - a reduced level of oxygen in tissues

Hysterectomy - surgical removal of the uterus

Hysteria - a term used to describe symptoms that are caused by mental stress and occur in someone who does not have a mental disorder

Hysterosalpingography - an X-ray examination performed to examine the inside of the uterus and fallopian tubes, in order to investigate and possibly treat infertility

Hysteroscopy - a method used to examine the inside of the uterus and the cervix using a viewing instrument

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