Online Medical Dictionary

Letter H

H: Symbol for hydrogen.
Hairy Cell Leukemia: A sub-type of chronic lymphoid leukemia marked by a build up of abnormal B lymphocytes, which appear hairy when viewed under microscope.
Halitosis: Odorous breath.
Hamartoma: A benign tumour-like malformation of the tissue, resembling a neoplasm. Hamaratoma will consist of a hodgepodge of cells and tissues that are normally found in the area in which they are growing, but these develop in an unorganized mass, generating no symptoms.
Hammer: The malleus bone found in the ear.
Hammer Toe: A deformity occurring in a joint of the second, third or fourth toe, causing the toe to be bent in a hammer-like form, but not completely rotated. Treatment can usually be sought in the form of physical therapy and special shoes, though orthopedic surgery can be used to correct the formation when necessary.
Hamstring: The posterior thigh muscles and/or the tendons situated posterior, or in back, of the knee.
Hand, Foot and Mouth Disease: A common condition affecting mainly infants and children, marked by fever, rash on the hands, mouth and feet, nausea and fever.
Hansen Disease: Leprosy; a chronic granulomatous infection of the peripheral nerves and upper respiratory tract mucosa causing skin lesions. Incited by the bacterium Mycobacterium leprae.
HDV: Abbreviation for hepatitis D virus.
Heart Attack: Acute myocardial infarction. Blood supply to the heart is interrupted, usually due to a blockage and rupture of fatty deposits or plaque in the coronary artery, causing the death of heart cells. If sustained, the lack of oxygen to the heart can cause the death of the tissue of the heart muscle, resulting in chest pain, shortness of breath, anxiety and sweating.
Heart Disease: A term used to describe any disease or condition affecting the heart. Cardiac disease is the leading cause of death in Canada and the United States.
Heart Failure: The heart's inability to supply the blood flow required for the human body to function normally. Causes can include heart attack, hypertension, cardiomyopathy and other forms of heart disease. Heart failure is common, and can be fatal. Symptoms include coughing, shortness of breath, swelled ankles and chronic venous congestion.
Heart Murmur: An extra heart sound caused by turbulent blood flow sufficient enough to become audible, usually via stethoscope. Physiologic murmurs are caused by structures outside of the heart, and tend to be benign, while pathologic murmurs indicate a cardiac problem such as a leaking heart valve or abnormal passageway through which blood is flowing.
Heart Muscle: The cardiac muscle; the myocardium.
Heart Rate: The number of times in which the heart beats within a specified time lapse, usually within one minute (beats per minute, or BPM). Heart rate can be felt in the pulse, usually at the wrist or neck, and changes based on oxygen flow, such as during rest or exercise. Heart rate can be used to determine various medical conditions.
Hedonophobia: An abnormal fear of pleasure.
Helper Cells: T cells, a type of white blood cell or leukocyte, which function to support the immune system by activating and directing immune B cells and T cells when an antigen is detected.
Hemarthrosis: Bleeding in a joint, usually occurring after an injury is incurred or in those predisposed to hemorrhage due to hemophilia or certain anticoagulant medications.
Hematemesis: Vomit containing blood.
Hematochezia: Stool containing blood.
Hematocrit: The proportion of blood volume packed with red blood cells, usually dependent on body size, thus the percentage of hematocrit volume averages are higher in males than females. Also termed erythrocyte volume fraction and packed cell volume (PCV).
Hematologist: A physician specialized in the diagnostics, treatment and prevention of conditions or disease pertaining the blood, the vascular systems and the bone marrow.
Hematology: The study of blood, the vascular systems and bone marrow.
Hematology-Oncology: The diagnostics, treatment, prevention and general study of blood disease, conditions and their relation to cancer.
Hematoma: A localized collection of blood, usually situated within tissue or muscle, as a result of hemorrhage or trauma.
Hematophobia: An abnormal fear of blood.
Hematopoiesis: The production of blood cellular components. The average human body produces millions of new blood cells every day through hematopoiesis in order to maintain normal circulation levels.
Hematuria: Urine containing blood.
Hemi-: Prefix defining a half.
Hemiparesis: Weakness affecting one side of the body.
Hemiplegia: Paralysis affecting one side of the body.
Hemochromatosis: A genetic metabolic disorder characterized by the overproduction and storage of iron in the body. Hemochromatosis may give the skin a bronze colour and cause damage to the liver and/or alternate organs.
Hemodialysis: A dialysis procedure used when kidneys are in renal failure, or unable to function normally, serving to remove waste products from the blood and allow ultrafiltration by a process of diffusion through a semipermeable membrane.
Hemoglobin: The oxygen-transporting and iron carrying metalloprotein of the red blood cells. When oxygenated hemoglobin reacts to become a virulent red. When depleted of oxygen hemoglobin appears blue.
Hemoglobinuria: Urine containing hemoglobin, darkening the urine colour; symptomatic of various conditions.
Hemophilia: A group of genetic disorders impeding the body's ability to effectively blood clot when a blood vessel breaks. As hemophilia is an X-linked disorder, the condition is more prevalent in men than women.
Hemophobia: An abnormal fear of blood.
Hemoptysis: The coughing up and/or expectorating of bloody sputum.
Hemorrhage: Loss of blood, internally or through a natural opening of the body, from the circulatory system. Humans can normally withstand up to a 15 per cent loss of total blood volume. When blood loss exceeds this value, it is termed desanguination.
Hemorrhoid: Vascular structures situated in the walls of the anal canal, serving to control the release of stool. These can become inflamed due to chronic diarrhea or constipation. When internal, hemorrhoids tend to cause no discomfort other than producing blood in the stool. When external hemorrhoids can cause some pain. Treatment includes a change in diet and in some cases surgery.
Hemostasis: The body's process to bring bleeding or hemorrhage to cessation.
Hepatic Biopsy: Biopsy of the liver.
Hepatic Transplant: Liver transplant.
Hepatitis: Inflammation of the liver caused by a hepatitis virus, infection, toxin or other disease.
Hepatitis A: An acute, infectious liver disease, prevalent mainly in developing countries, caused by the hepatitis A virus and transmitted though contaminated food, liquid or directly from person to person.
Hepatitis B: A highly infectious liver disease incited by the hepatitis B virus, transmitted through infectious blood and body fluid, such as through used needles, transfusion or childbirth. Nearly one third of the global population have been infected by hepatitis B.
Hepatitis C: Disease of the liver incited by the hepatitis C virus, which is usually transmitted by blood exchange. Though the hepatitis C virus may not produce symptoms itself, the virus can incite fibrosis, cirrhosis, or liver cancer.
Hepatoblastoma: A rare malignant neoplasm of the liver which can occur in infants or young children, developing from the liver cells or bile ducts.
Hepatocarcinoma: See Hepatocellular Carcinoma
Hepatocellular Carcinoma: Cancerous hepatoma or malignancy of the liver; usually progressing from a hepatitis virus or cirrhosis, the primary liver cancer of developing countries. In developed countries the primary cause of liver cancer is the metastasis of cancer from another malignant area of the body.
Hepatoma: Cancer originating from a malignant tumour of the liver. See Hepatocellular Carcinoma.
Hepatomegaly: A liver that has become enlarged, due to any of a variety of factors including tumour, metabolic disorder, infection or toxin.
Hepatotoxic: Liver injury or damage incited by chemical effect.
Heritability: The degree to which something is genetically passed down to offspring.
Hermansky-Pudlak Syndrome: A rare genetic disorder with eight forms, marked by albinism, accumulation of an abnormal fat-protein and a bleeding condition due to a defect in platelet storage.
Hernia: A protrusion or fascia of an organ through the wall of the cavity in which it is usually held.
Herniorrhaphy: A surgical procedure to repair the effects of hernia.
Herpes Simplex Virus: Herpes simplex virus (HSV) type 1 and 2 belong to the Herpesviridae family, and are contagious from person to infected person when the infected person is shedding. Herpes simplex virus manifests in the forms of blisters, which may appear on the mouth, labia or genitals.
Heterotaxy: A rare condition causing the organs to place abnormally within the abdomen and chest. Also termed situs ambiguous.
Heterotopic: Located out of position; abnormally located.
Hidrosis: The body process of sweating.
High Blod Pressure: Hypertension; blood pressure the repeatedly exceeds a systolic pressure of 140 with a diastolic pressure of 90.
High Blood Sugar: See Hyperglycemia.
Hippocampus: A member of the limbic system of the brain, key in spacial navigation and long-term memory. The hippocampus is one of the first areas damaged in the course of Alzheimer's disease.
Hippophobia: An abnormal fear of horses.
Histamine: A nitrogen compound that triggers an inflammatory immune response, increasing the permeability of the capillaries to white blood cells and proteins, enabling their faster access to foreign pathogens.
Hodgkin Lymphoma: A form of lymphoma, a cancer that develops from the white blood cells of the body's immune system, the lymphocytes. Hodgkins lymphoma begins from a single lymph node, usually in the neck. Also referred to as Hodgkin Disease.
Hormone: A chemical substance that when released, by gland or cell, communicates an effect to another cell or organ in the body.
Hormone Therapy: Medical treatment involving the use of hormones. Can be encompassed in the treatment of cancer, aging, hormonal deficiency, sex reassignment therapy, and chemical castration.
Hospice: A palliative care facility or program, providing emotional, physical and spiritual end of life care for the terminally ill and their families.
HPV: Abbreviation for Human Papillomavirus.
Human Immunodeficiency Virus (HIV): Lentivirus belonging to the retrovirus family causing the acquired immune deficiency syndrome, AIDS. HIV is transmitted through the transfer of blood, semen and breast milk.
Human Papillomavirus (HPV): An infection that develops in the epithelium of the skin or mucous membranes. HPV can be asymptomatic or cause warts and precancerous legions. Left untreated, HPV has the potential to form into cancer of the cervix, anus, vagina or vulva in females and cancer of the anus or penis in males.; The long arm bone running from the elbow to the shoulder.
Huntington's Disease: A a neurodegenerative hereditary disorder affecting muscle coordination, deteriorating cognitive abilities and inducing dementia. Caused by an autosomal dominant mutation on the gene Huntingtin. Treatment can reduce the effects of the disease.
Hydrophobia: An abnormal fear of water.
Hyper-: Prefix defining in excess.
Hypercalcemia: An abnormally high level of calcium in the blood. May be asymptomatic or indicative of disease, such as an abnormal parathyroid gland function, breast cancer, lung cancer, kidney cancer, lymphoma, leukemia, renal failure, hyperthyroid, or a metabolic disorder of vitamin D.
Hypercapnia: Abnormal levels of carbon dioxide in the blood. May be responsible in some cases of sudden infant death syndrome.
Hyperekplexia: A genetic neurological disorder linked to gene defects or brain trauma, causing pronounced startled responses to stimuli.
Hyperglycemia: An elevated level of glucose in the blood, which can be caused by diabetes mellitus, certain medications, stress or other critical illness.
Hyperopia: Farsightedness.
Hyperplasia: Abnormal cell growth in a tissue or organ, which may cause the organ to become grossly enlarged. Can be induced by a chronic inflammatory response, disease or a hormonal dysfunction.
Hypertension: See High Blood Pressure.
Hyperthyroid: Excess of thyroid hormone resulting from an overactive thyroid gland (or taking too much thyroid hormone). Symptoms can include increased heart rate, weight loss, depression, and cognitive slowing.
Hypertrophy: Unlike hyperplasia, in which organs enlarge due to an increase in cell number, hypertrophy involves the enlargement of an organ or tissue as a result of the increase in the composing cells size.
Hyperventilation: Taking in breath at a rate that is faster than normal. May result from anxiety or other disorder and cause dizziness, faintness and headache.
Hypnolepsy: Narcolepsy.
Hypo-: Prefix defining below or less than normal.
Hypochondriac: An individual excessively preoccupied with normal body functions and sensations, misinterpreting them as signs of illness, poor health or disease; an individual illustrating the somatoform disorder hypochondriasis.
Hypoglycemia: Low levels of glucose in the blood. May occur as result of excessive insulin intake or production, metabolic dysfunctions, medications, malnutrition, alcohol consumption, hormone deficiency or poisoning. Results in impaired function, and in severe cases seizure or unconsciousness.
Hypoplasia: A congenital condition causing the underdevelopment of an organ or tissue, usually as a result of a less than normal production of composite cells. Hypoplasia may manifest in a variety of anatomical areas, including the ovaries, teeth, fingers or lungs.
Hypopnea: The shallower or slower intake of breath than is normal. Can be an aspect of a sleep disorder, resulting in a decrease in the level of oxygen in the blood, or occur during daytime and compromise respiratory muscles.
Hyposmia: An impeded ability to smell. May be a symptom in the early onset of Parkinson's Disease.
Hypotension: Blood pressure below that which is expected for the individual; generally blood pressure that measures less than 90 over 60. Usually occurs as a result of shock, certain medications, changes in hormonal levels or anemia.
Hypothalamus: The area of the brain linking the endocrine system, via the pituitary gland, to the nervous system, responsible for metabolic processes, thereby functioning to control hunger, thirst, fatigue and body temperature.
Hypothyroidism: A deficient production of the thyroid hormone, most often due to an abnormality of the thyroid gland. Can result from an iodine deficiency, exposure to nuclear iodine, or an absent thyroid gland.
Hypoxemia: Less than normal levels of oxygen in the blood; or an oxygen saturation of less than 90 per cent in the hemoglobin, induced from any of a variety of causes including low oxygen pressure or hypoventilation.
Hysterectomy: Total or partial removal of the uterus by surgical procedure. A complete hysterectomy also involves the removal of the cervix. As hysterectomy has a significant affect on female hormonal levels and removes the possibility for future childbirths, thus the procedure is usually retained in cases where cancer, endometriosis, postpartum placenta or excessive bleeding are present.