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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


a purple-red mark on the skin, caused by an excess of blood vessels


bleeding into and swelling of a joint


vomiting of blood


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


an accumulation of blood from a broken blood vessel


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


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


a method used to treat kidney failure, in which blood is passed through a machine that purifies it and returns it to the body


the pigment in red blood cells that is responsible for carrying oxygen; haemoglobin bound to oxygen gives blood its red colour


haemoglobin in the urine


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


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


the medical term for bleeding


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


blood in the semen


the stopping of bleeding by the body's mechanisms


an accumulation of blood between the chest wall and the lungs

Hair follicle

a tiny opening in the skin from which a hair grows


the clinical term for bad breath; commonly caused by poor oral hygiene or eating certain foods; if persistent it can be a sign of illness


a perception that occurs when there is actually nothing there to cause it (such as hearing voices when there are none)

Hammer toe

an abnormality in the tendons of the toe that causes the toe to be flexed at all times

Hamstring muscle

a muscle located at the back of the thigh that bends the leg at the knee and moves the leg backward

Hardening of the arteries

the common name for arteriosclerosis

Hashimoto's thyroiditis

Hashimoto's thyroiditis or Hashimoto's disease is an autoimmune disease where the body's immune system attacks cells of the thyroid gland, resulting in lower production of thyroid hormones. Hashimoto's disease is named after Hakaru Hashimoto who first described it in 1912.

Hay fever

the common name for allergic rhinitis


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

Heart disease

see Coronary heart disease

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

Heart-lung machine

a machine that takes over the functions of the heart and lungs during certain types of surgery


a burning sensation experienced in the centre 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

Heat exhaustion

fatigue, dizziness, and nausea experienced because of overexposure to heat; if not treated it can result in heat stroke

Heat stroke

a life-threatening condition resulting from extreme overexposure to heat, which disrupts the body's system of regulating temperature

Heel spur

an abnormal, often painful outgrowth of bone on the back of the heel

Heimlich manoeuvre

a first-aid technique for choking; dislodges an object that is blocking a person's airway

Helper T cells

white blood cells, responsible for regulating other cells in the body's immune system, that are the main targets of the AIDS virus; also called CD4 cells


surgical removal of all or part of the liver


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


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


a cancerous tumour of the liver


enlargement of the liver


describes a genetic trait that is passed from parents to children

Hereditary spherocytosis

a genetic disorder in which red blood cells are smaller, rounder, and more fragile than normal, causing haemolytic anaemia


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


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

Herniated disk

see Disk prolapse

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 blister-like sores on the face, lips, mouth, or genitals; in rare cases, can also affect the eyes, fingers, or brain

Herpes zoster

see Shingles


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


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

Hirschsprung's disease

a condition that is present at birth in which nerve cells do not develop in parts of the intestine, causing the intestine to narrow and block the passage of faeces


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


Histamine is a chemical that is frequently involved in allergic reactions and is released by specialised blood cells called basophils and mast cells. Histamine causes swelling of the local tissues (which if in the nose or throat can cause blocked nose and difficulty breathing), increased blood flow into that area causing redness and the release of other substances such as kinins that cause itching.


a respiratory disease acquired by inhaling the spores of a fungus found in soil, especially where there are bird or bat droppings


see Human immunodeficiency virus


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

Hodgkin's disease

a cancer of lymphoid tissue (found in lymph nodes and the spleen) that causes the lymph nodes to enlarge and function improperly; may cause illness, fever, loss of appetite, and weight loss


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


a genetic disorder in which an enzyme deficiency causes a substance called homocystine to build up in the blood, leading to mental handicap and skeletal abnormalities


being sexually attracted to members of the same sex


infestation by a small, round, blood-sucking parasite; commonly causes a rash on the foot, but can also cause cough, pneumonia, and anaemia

Hormonal implant

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


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


a hospital or an area of a hospital dedicated to treating people who are dying, often of a specific cause

Hot flush

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


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 leukaemia or T-cell lymphomas


an excess of amniotic fluid in the uterus during pregnancy


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


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


a corticosteroid drug that is used to treat inflammation and allergies


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


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


a type of behaviour characterised by excessive physical activity, sometimes associated with neurological or psychological causes


a method of providing nutrients by the use of a tube or intravenously to a person who cannot eat food or needs nutrients because of an illness


a condition in which there is too much bilirubin, a substance produced when red blood cells are broken down; can lead to jaundice


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


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


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


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


over-activity of the parathyroid glands, which increases calcium levels in the blood (called hypercalcaemia) and decreases calcium in bones (causing osteoporosis)


the enlargement of an organ or tissue


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


abnormally high blood pressure, even when at rest


an abnormally high body temperature


Hyperthyroidism is the name given to an overactive thyroid gland, causing nervousness, weight loss, fatigue, diarrhoea and a host of other symptoms.


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


abnormally rapid breathing


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


abnormally low levels of glucose in the blood


failure of a tissue or organ to develop normally


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


an abnormally low body temperature


Hypothyroidism is the term given to an underactive thyroid gland, causing tiredness, cramps, a slowed heart rate, weight gain and a host of other symptoms.


a slower-than-normal breathing rate


a reduced level of oxygen in the blood


a reduced level of oxygen in tissues


surgical removal of the uterus


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


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


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

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