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H2-blockers - medications used to treat gastroesophageal reflux disease (GERD) that decrease the amount of acid made by the stomach. The stomach lining has sites that react to a chemical normally found in the body called histamine. When histamine attaches to these sites, the stomach produces acid that aids in digestion of food. H2-blockers prevent the stomach from reacting to histamine, thereby decreasing stomach acid.
Haemophilus influenzae (Also called H. influenzae.) - a group of bacteria that may cause different types of infections in infants and children. H. influenzae most commonly causes ear, eye, or sinus infections, and pneumonia.
Hair cells - sensory cells of the inner ear, which are topped with hair-like structures (stereocilia), which transform the mechanical energy of sound waves into nerve impulses.
Halitosis - an oral health condition characterized by consistently odorous breath.
Hallucinations - a strong perception of an event or object when no such situation is present; may occur in any of the senses (i.e., visual, auditory, gustatory, olfactory, or tactile).
Hammertoe - a sideways bend in the middle toe joint that affects the second, third, or fourth toe. It is caused by wearing ill-fitting shoes over a long period of time and/or an imbalance of muscles in the foot.
Hamstrings - three large muscles located in the back side of each thigh.
Handicap - a condition caused by illness or injury, or present from birth that prevents a person from performing some activities of daily living, as well as other activities, such as school or work.
Hay fever (also called rhinitis) - an inflammation of the mucous membrane that lines the nose, often due to allergy to pollen, dust or other airborne substances, which causes sneezing, itching, a runny nose, and nasal congestion.
Headache - pain or discomfort in the head or face area. Headaches can be single or recurrent in nature, and localized to one or more areas of the head and face.
Headache (primary) - includes tension (muscular contraction), vascular (migraine), and cluster headaches not caused by other underlying medical conditions.
Headache (secondary) - includes headaches that result from other medical conditions. These may also be referred to as traction headaches or inflammatory headaches.
Hearing - series of events in which sound waves in the air are converted to electrical signals that are sent as nerve impulses from the ear to the brain, where they are interpreted.
Hearing aid - electronic device that brings amplified sound to the ear.
Hearing disorder - disruption in the normal hearing process; sound waves are not converted to electrical signals and nerve impulses are not transmitted to the brain to be interpreted.
Heart attack (also called myocardial infarction) - occurs when one of more regions of the heart muscle experience a severe or prolonged decrease in oxygen supply caused by a blocked blood flow to the heart muscle.
Heart block - interrupted electrical impulse to heart muscles.
Heart rate - the rate at which the heart beats. Normal heart rates range between 60 and 100 beats per minute.
Heart valve prolapse - a condition of the heart valve, specifically the mitral valve, in which it is partially open when it should be closed.
Heartbeat - one complete contraction of the heart.
Heartburn - painful, burning feeling in the chest caused by stomach acid flowing back into the esophagus.
Heart-lung machine - a machine that performs the functions of the heart and lungs during open heart surgery by pumping blood, as well as providing oxygen in the blood that is pumped. This allows the heart and lungs to be completely still while surgery is performed.
Heat exhaustion - a form of heat-related illness that is more severe than heat cramps and results from a loss of water and salt in the body. It occurs in conditions of extreme heat and excessive sweating without adequate fluid and salt replacement. Heat exhaustion occurs when the body is unable to cool itself properly. If left untreated, heat exhaustion can progress to heat stroke.
Heat stroke - the most severe form of heat illness and is a life-threatening emergency. It is the result of long, extreme exposure to the sun, in which a person does not sweat enough to lower body temperature.
Heel spur - a bone growth on the heel bone.
Heimlich maneuver - an emergency first aid treatment consisting of a series of under-the-diaphragm abdominal thrusts used on a person choking on food or a foreign object. In the case of a pregnant woman, the thrusts can be delivered over the breastbone instead of the abdomen.
Helicobacter pylori (H. pylori) - a spiral-shaped bacterium found in the stomach. H. pylori damages stomach and duodenal tissue, causing ulcers; previously called Campylobacter pylori.
Hemarthrosis - bleeding into a joint.
Hematocrit - the measurement of the percentage of red blood cells found in a specific volume of blood.
Hematologist - a physician who specializes in the functions and disorders of the blood.
Hematology - the scientific study of blood and blood-forming tissues.
Hematoma - blood that collects under the skin or in an organ.
Hematopathology - the study of blood, bone marrow, and the organs and tissues that use blood cells to perform their functions.
Hematopoiesis - the process of producing and developing new blood cells.
Hematuria - the presence of red blood cells (RBCs) in the urine.
Hemochromatosis (also called iron overload disease) - a metabolic disorder that causes increased absorption of iron, which is deposited in the body tissues and organs. The iron accumulates in the body where it may become toxic and cause damage.
Hemoglobin - a protein in red blood cells that bonds with oxygen, carrying it to the cells of the body.
Hemoglobin A1c (also called HbA1c test) - a blood test that shows the average amount of glucose (sugar) in the blood over the last three months. The result will indicate if the blood sugar level is under control.
Hemolytic anemia - one type of anemia in which the red blood cells are destroyed prematurely.
Hemolytic uremic syndrome - a rare kidney disorder that mostly affects children under the age of 10. It is often characterized by damage to the lining of blood vessel walls, destruction of red blood cells, and/or kidney failure. It is caused by toxic substances released during an infection, most often from E. coli O157:H7; however, other organisms can also cause it.
Hemophilia (also called coagulation disorder) - a group of bleeding disorders caused by low levels, or absence of, a blood protein that is essential for clotting; hemophilia A is caused by a lack of the blood clotting protein factor VIII; hemophilia B is caused by a deficiency of factor IX; von Willebrand disease is caused by a deficiency of the von Willebrand factor.
Hemorrhage - the medical term for bleeding.
Hemorrhoidectomy - the surgical removal of hemorrhoids.
Hemorrhoids - swollen blood vessels in and around the anus that cause itching, pain, and sometimes bleeding.
Hepatic - related to the liver.
Hepatitis - inflammation of the liver that sometimes causes permanent damage; caused by viruses, drugs, alcohol, or parasites. Hepatitis has several forms:
Hepatitis A - a form of infectious hepatitis caused by the hepatitis A virus. The virus may be spread by fecal-oral contact, fecal-infected food or water, and may also be spread by a blood-borne infection (which is rare).
Hepatitis B - a form of infectious hepatitis caused by the hepatitis B virus. Transmission of the hepatitis B virus occurs through blood and body fluid exposure such as blood semen, vaginal secretions, or saliva.
Hepatitis C - a form of infectious hepatitis caused by the hepatitis C virus. Transmission of the hepatitis C virus occurs primarily from contact with infected blood, but can also occur from sexual contact or from an infected mother to her baby.
Hepatitis D - a form of infectious hepatitis caused by the hepatitis D (Delta) virus. This form of hepatitis can only occur in the presence of hepatitis B. Transmission of hepatitis D occurs the same way as hepatitis B.
Hepatitis E - a form of infectious hepatitis caused by the hepatitis E virus. This form of hepatitis is similar to hepatitis A. Transmission occurs through fecal-oral contamination. Hepatitis E is most common in poorly developed countries and is rarely seen in the US.
Hepatitis G - the most recently discovered form of infectious hepatitis. Transmission is believed to occur through blood and is seen in IV drug users, individuals with clotting disorders, such as hemophilia, and individuals who require hemodialysis for renal failure.
Hepatologist - physician who specializes in liver diseases.
Hepatology - field of medicine concerned with the functions and disorders of the liver.
Hepatomegaly - enlarged liver.
Hernia - a protrusion of part of an organ through the muscle that surrounds it.
Herpes genitalis (also called genital herpes) - an infection caused by the herpes simplex virus (HSV) and usually spread by sexual contact. Symptoms may include painful blisters or open sores in the genital area, which may be preceded by a tingling or burning sensation in the legs, buttocks, or genital region. The herpes sores usually disappear within a few weeks, but the virus remains in the body and the lesions may recur from time to time.
Herpes zoster (also called shingles) - a viral infection of the nerves, characterized by a painful skin rash of small blisters anywhere on the body.
Hiatal hernia - small opening in the diaphragm that allows the upper part of the stomach to move up into the chest and causes heartburn from stomach acid flowing back up through the opening.
High blood glucose - a condition that occurs in people with diabetes when their blood glucose levels are too high.
High blood pressure - a condition in which the blood circulates through the arteries with too much force.
High-density lipoprotein (HDL) - a protein in the blood plasma that promotes breakdown and removal of cholesterol from the body.
Hip - the region on each side of the pelvis; made up of three sections: ilium, ischium, and pubis; the upper part of the femur (upper leg bone) fits into the hip via a ball-and-socket joint; the socket is a cup-shaped bone of the pelvis, called the acetabulum, and the ball is the head of the femur.
Hirschsprung's disease - a birth defect in which some nerve cells are lacking in the large intestine. As a result, a blockage occurs because the intestinal muscles cannot contract and push food through without being stimulated by nerves.
Hirsutism - excessive hairiness.
Histamine - a chemical present in cells throughout the body that is released during an allergic reaction and one of the substances responsible for the symptoms of inflammation.
Histrionic personality disorder - a condition in which a person is overly conscious of personal appearance, constantly seeks attention, and often behaves dramatically in situations that do not warrant this type of reaction. The emotional expressions of people with histrionic personality disorder are often judged as superficial and exaggerated.
Hives (also called urticaria) - a condition in which red, itchy, and swollen areas appear on the skin - usually as an allergic reaction from eating certain foods or taking certain medications.
Hoarseness - abnormally rough or harsh-sounding voice caused by vocal abuse and other disorders.
Hodgkin disease - a type of lymphoma, a cancer in the lymphatic system; a rare disease, accounting for less than 1 percent of all cases of cancer in the U.S., occurring most often in people between the ages of 15 and 34, and in people over age 55. Hodgkin disease causes the cells in the lymphatic system to abnormally reproduce, eventually making the body less able to fight infection. Steady enlargement of lymph glands, spleen, and other lymphatic tissue occurs.
Holter monitor - an electrocardiogram (ECG or EKG) recording done over a period of 24 or more hours, using a small, portable machine.
Hormone replacement therapy (HRT) - use of the female hormones estrogen and progestin (a synthetic form of progesterone) to replace those hormones the body no longer produces after menopause.
Hormone therapy - the use of hormones, medications, or surgery to suppress (block) or mimic hormones and alter the growth of hormone-sensitive cancer.
Hormones - chemical substances created by the body that control numerous body functions.
Hospice - literal meaning "a place of shelter." Today, hospice refers to supportive care of a terminally ill patient. Hospice care may be provided in a hospital, nursing home, assisted-living facility, or in the home.
Human chorionic gonadotropin - a hormone produced by the placenta about 10 days after fertilization.
Human papillomaviruses (HPVs) - a group of viruses that can cause warts. Some HPVs are sexually transmitted and cause wart-like growths on the genitals. HPV is associated with some types of cancer.
Humerus - the bone of the upper arm.
Hyaloid canal - a narrow passageway inside the eye that allows blood to flow through the eye in the fetus and fluid to move through the eye later in life.
Hydrochloric acid - acid made in the stomach that works with pepsin and other enzymes to break down proteins.
Hydrocortisone - a hormone secreted by the adrenal cortex that affects metabolism and the immune response.
Hydronephrosis - a condition that occurs as a result of urine accumulation in the upper urinary tract; usually occurs from a blockage somewhere along the urinary tract.
Hydrotherapy - rehabilitation exercises performed in water.
Hyperactive - describes a situation in which a body tissue is especially likely to have an exaggerated reaction to a particular situation.
Hyperextension - active or passive force which takes the joint into extension, but beyond its normal range.
Hyperglycemia (also called high blood glucose) - a condition that occurs in people with diabetes when their blood glucose levels are too high.
Hyperopia - farsightedness.
Hyperplasia - an abnormal increase in the number of cells in a tissue or an organ (i.e., cervix or the lining of the uterus).
Hypertension - abnormally high blood pressure.
Hypertrophic obstructive cardiomyopathy (HOCM) - a condition in which the heart muscle becomes thickened, which decreases the heart's ability to pump blood.
Hypertrophy - an increase in the size of tissue.
Hypogeusia - diminished sensitivity to taste.
Hypoglycemia - condition in which the blood sugar is lower than normal.
Hypomobility - a decrease in the normal range of joint movement.
Hyposmia - diminished sensitivity to smell.
Hypotension - abnormally low blood pressure.
Hypothalamus - small structure at the base of the brain that regulates many body functions, including appetite, body temperature, and stimulation of the pituitary gland.
Hypothermia - an abnormally low body temperature brought on by staying in cold temperatures for a long period of time; a life-threatening emergency.
Hypoxia - abnormally low oxygen content in the organs and tissues of the body.
Hysterectomy - surgical removal of the uterus.
Hysterosalpingography - X-ray examination of the uterus and fallopian tubes that uses dye and is often performed to rule out tubal obstruction.
Hysteroscope - a viewing instrument inserted through the vagina for a visual examination of the canal of the cervix and the interior of the uterus.
Hysteroscopy - a visual examination of the canal of the cervix and the interior of the uterus using a viewing instrument (hysteroscope) inserted through the vagina.