The British Medical Association ILLUSTRATED MEDICAL DICTIONARY CORONARY ARTERY Superior vena cava Pulmonary veins Right main coronary artery Aorta Left main coronary artery Left circumflex artery Left anterior descending artery Coronary vein Inferior vena cava Descending aorta coronary Any structure that encircles like a crown The term usually refers to the coronary arteries encircling the heart It is also sometimes used as a nonmedical term for a heart attack (see myocardial infarction) coronary artery Either of the main arteries that supply the tissues of the heart with oxygen-rich blood These arteries, known as the left and right main coronary arteries, arise directly from the aorta The term coronary artery is also applied to any of the arteries that branch off from the main coronary arteries, such as the left circumflex artery and the left anterior descending artery Blockage of a coronary artery as a result of atherosclerosis can lead to myocardial infarction (See also coronary artery disease.) Essential A–Z quick reference to over 5,500 medical terms The British Medical Association ILLUSTRATED MEDICAL DICTIONARY A Dorling Kindersley Book ABDOMEN A ABDOMINAL SWELLING intake, eating unwisely, or an attack of diarrhoea Pain in the lower abdomen is common during menstruation but is occasionally due to a gynaecological disorder such as endometriosis Cystitis is a common cause of pain or discomfort in the abdomen Bladder distension as a result of urinary obstruction may also cause abdominal pain Abdominal colic is pain that occurs every few minutes as one of the internal organs goes into muscular spasm in an attempt to overcome an obstruction such as a stone or an area of inflammation The attacks of colic may become more severe and may be associated with vomiting (see abdomen, acute) Peptic ulcer often produces recurrent gnawing pain Other possible causes of abdominal pain are infection, such as pyelonephritis, and ischaemia (lack of blood supply), as occurs when a volvulus (twisting of the intestine) obstructs blood vessels Tumours affecting an abdominal organ can cause pain Abdominal pain can also result from anxiety For mild pain, a wrapped hot-water bottle is often effective Pain due to peptic ulcer can be temporarily relieved by food or by taking antacid drugs Abdominal pain that is not relieved by vomiting, persists for more than hours, or is associated with sweating or fainting requires urgent medical attention Urgent attention is also necessary if pain is accompanied by persistent vomiting, vomiting of blood, or passing of bloodstained or black faeces Unexplained weight loss or changes in bowel habits should always be investigated Investigation of abdominal pain may include the use of imaging tests such as ultrasound scanning, and endoscopic examination in the form of gastroscopy, colonoscopy, or laparoscopy abdominal swelling Enlargement of the abdomen Abdominal swelling is a natural result of obesity and growth of the uterus during pregnancy Wind in the stomach or intestine may cause uncomfortable, bloating distension of the abdomen Some women experience abdominal distension due to temporary water retention just before menstruation Other causes may be more serious A abdomen The region of the body between the chest and the pelvis The abdominal cavity is bounded by the ribs and diaphragm above, and by the pelvis below, with the spine and abdominal muscles forming the back, side, and front walls It contains the liver, stomach, intestines, spleen, pancreas, and kidneys In the lower abdomen, enclosed by the pelvis, are the bladder, rectum, and, in women, the uterus and ovaries ABDOMEN Stomach Liver Large intestine Area of abdomen Small intestine Rectum abdomen, acute Persistent, severe abdominal pain of sudden onset, usually associated with spasm of the abdominal muscles, vomiting, and fever The most common cause of an acute abdomen is peritonitis Other causes include appendicitis, abdominal injury, perforation of an internal organ due to disorders such as peptic ulcer or diverticular disease Acute abdominal pain commonly begins as a vague pain in the centre but then becomes localized An acute abdomen requires urgent medical investigation that may involve a laparoscopy or a laparotomy Treatment depends on the underlying cause abdominal pain Discomfort in the abdomen Mild abdominal pain is common and is often due to excessive alcohol ABDOMINAL THRUST ABSCESS For instance, ascites (accumulation of fluid between organs) may be a symptom of cancer or disease of the heart, kidneys, or liver; swelling may also be due to intestinal obstruction (see intestine, obstruction of) or an ovarian cyst Diagnosis of the underlying cause may involve abdominal X-rays, ultrasound scanning, laparotomy, or laparoscopy In ascites, some fluid between organs may be drained for examination abdominal thrust A first-aid treatment for choking, in which sharp upward pressure is applied to the upper abdomen to dislodge a foreign body obstructing the airway The technique is also known as the Heimlich manoeuvre abdominal X-ray An X-ray examination of the abdominal contents X-rays can show whether any organ is enlarged and can detect swallowed foreign bodies in the digestive tract They also show patterns of fluid and gas: distended loops of bowel containing fluid often indicate an obstruction (see intestine, obstruction of); gas outside the intestine indicates intestinal perforation Calcium, which is opaque to X-rays, is present in most kidney stones (see calculus, urinary tract) and in some gallstones and aortic aneurysms; these can sometimes be detected on an abdominal X-ray abducent nerve The 6th cranial nerve It supplies the lateral rectus muscle of each eye, which is responsible for moving the eyeball outwards The nerve originates in the pons (part of the brainstem) and passes along the base of the brain, entering the back of the eye socket through a gap between the skull bones abduction Movement of a limb away from the central line of the body, or of a digit away from the axis of a limb Muscles that carry out this movement are called abductors (See also adduction.) ablation Removal or destruction of diseased tissue by excision (cutting away), cryosurgery (freezing), radiotherapy, diathermy (burning), or laser treatment abnormality A physical deformity or malformation, a behavioural or mental problem, or a variation from normal in the structure or function of a cell, tissue, or organ in the body ABO blood groups See blood groups abortifacient An agent that causes abortion In medical practice, abortion is induced using prostaglandin drugs, often given as vaginal pessaries abortion In medical terminology, either spontaneous abortion (see miscarriage) or medically induced termination of pregnancy (see abortion, induced) abortion, induced Medically induced termination of pregnancy Abortion may be performed if continuation of the pregnancy would risk the woman’s life, if the mental or physical health of the woman or her existing children is at risk, or if there is a substantial risk of handicap to the baby Depending on the stage of pregnancy, termination may be induced by using drugs or by the surgical technique of vacuum suction curettage, under either a general or local anaesthetic, during which the fetal and placental tissues are removed Complications are rare abrasion Also called a graze, a wound on the skin surface that is caused by scraping or rubbing abrasion, dental The wearing away of tooth enamel, often accompanied by the erosion of dentine (the layer beneath the enamel) and cementum (the bonelike tissue that covers the tooth root), usually through too-vigorous brushing Abraded areas are often sensitive to cold or hot food or drink, and a desensitizing toothpaste and/or protection with a bonding (see bonding, dental) agent or filling may be needed abreaction In psychoanalysis, the process of becoming consciously aware of repressed (buried) thoughts and feelings In Freudian theory, abreaction ideally occurs by way of catharsis abscess A collection of pus formed as a result of infection by microorganisms, usually bacteria Abscesses may develop in any organ and in the soft tissues beneath the skin in any area Common sites include the armpit, breast (see breast abscess), groin, and gums (see abscess, dental) Rarer sites include the liver (see liver abscess) and the brain (see brain abscess) Common bacteria, such as staphylococci, are the usual cause of abscesses, A A ABSCESS, DENTAL ACANTHOSIS NIGRICANS although fungal infections can cause them, and amoebae are an important cause of liver abscesses (see amoebiasis) Infectious organisms usually reach internal organs via the bloodstream, or they penetrate tissues under the skin through a wound An abscess may cause pain, depending on where it occurs Most larger abscesses cause fever, sweating, and malaise Those that are close to the skin often cause obvious redness and swelling Antibiotics, antifungal drugs, or amoebicides are usually prescribed as appropriate Most abscesses also need to be drained (see drain, surgical), and in some cases a tube may be left in place to allow continuous drainage Some abscesses burst and drain spontaneously Occasionally, an abscess within a vital organ damages enough surrounding tissue to cause permanent loss of normal function, or even death abscess, dental A pus-filled sac in the tissue around the root of a tooth An abscess may occur when bacteria invade the pulp (the tissues in the central cavity of a tooth) as a result of dental caries, which destroys the tooth’s enamel and dentine, allowing bacteria to reach the pulp Bacteria can also gain access to the pulp when a tooth is injured The infection in the pulp then spreads into the surrounding tissue to form an abscess Abscesses can also result from periodontal disease, in which bacteria accumulate in pockets that form between the teeth and gums The affected tooth aches or throbs, and biting or chewing is usually extremely painful The gum around the tooth is tender and may be red and swollen An untreated abscess eventually erodes a sinus (channel) through the jawbone to the gum surface, where it forms a swelling known as a gumboil As the abscess spreads, the glands in the neck and the side of the face may become swollen, and fever may develop Treatment may consist of draining the abscess, followed by root-canal treatment of the affected tooth, but in some cases extraction of the tooth is necessary Antibiotics are prescribed if the infection has spread beyond the tooth ABSCESS, DENTAL Enamel Dentine Decay Gum Pulp Blood vessel Nerve Jawbone Abscess An abscess in a periodontal pocket can usually be treated by the dentist scraping away infected material absence In medical terms, a temporary loss or impairment of consciousness that occurs in some forms of epilepsy, typically generalized absence (petit mal) seizures in childhood absorption The process by which fluids or other substances are taken up by body tissues The term is commonly applied to the uptake of the nutrients from food into blood and lymph from the digestive tract The major site of absorption is the small intestine, which is lined with microscopic finger-like projections called villi (see villus) The villi greatly increase the surface area of the intestine, thereby increasing the rate of absorption acanthosis nigricans A rare condition in which thickened dark patches of skin appear in the groin, armpits, neck, and other skin folds The condition may occur in young people as a genetic disorder or as the result of an endocrine disorder such as Cushing’s syndrome It also occurs in people with carcinomas of the lung and other organs Pseudoacanthosis nigricans is a much more common condition, usually seen in dark-complexioned people who are overweight In this form, the skin in fold areas is both thicker and darker than the surrounding skin, and there is usually excessive sweating in affected areas The condition may improve with weight loss ACARBOSE ACETYLCHOLINESTERASE INHIBITORS more difficult and results in a form of longsightedness called presbyopia acebutolol A beta-blocker drug used to treat hypertension, angina pectoris, and certain types of arrhythmia in which the heart beats too rapidly ACE inhibitor drugs A group of vasodilator drugs used to treat heart failure, hypertension, and diabetic nephropathy ACE (angiotensin converting enzyme) inhibitors are often prescribed with other drugs such as diuretic drugs or betablocker drugs Possible side effects include nausea, loss of taste, headache, dizziness, and dry cough acetaminophen An analgesic drug more commonly known as paracetamol acetazolamide A drug that is used in the treatment of glaucoma and, occasionally, to prevent or treat symptoms of mountain sickness Possible adverse effects include lethargy, nausea, diarrhoea, and impotence acetic acid The colourless, pungent, organic acid that gives vinegar its sour taste In medicine, acetic acid is an ingredient of antiseptic gels that are used for certain vaginal infections acetylcholine A type of neurotransmitter (a chemical that transmits messages between nerve cells or between nerve and muscle cells) Acetylcholine is the neurotransmitter found at all nervemuscle junctions and at many other sites in the nervous system The actions of acetylcholine are called cholinergic actions, and these can be blocked by anticholinergic drugs acetylcholinesterase inhibitors A group of drugs that are used in the treatment of mild to moderate dementia due to Alzheimer’s disease, in which there is a deficiency of the neurotransmitter acetylcholine in the brain acarbose A drug that is used to treat type diabetes mellitus Acarbose acts on enzymes in the intestines, inhibiting the digestion of starch and therefore slowing the rise in blood glucose levels after a carbohydrate meal accessory nerve The 11th cranial nerve Unlike the other cranial nerves, most of the accessory nerve originates from the spinal cord The small part of the nerve that originates from the brain supplies many muscles of the palate, pharynx (throat), and larynx (voice box) Damage to this part of the nerve may cause difficulty in speaking and swallowing The spinal part of the nerve supplies large muscles of the neck and back, notably the sternomastoid and trapezius Damage to the spinal fibres of the nerve paralyses these muscles accidental death Death that occurs as a direct result of an accident A high proportion of deaths in young adults, particularly among males, are accidental Many of these deaths are due to road traffic accidents, drowning, or drug overdose Falls in the home and burning or asphyxiation due to fire are common causes of accidental death in elderly people Fatal accidents at work have become less common with the introduction of effective safety measures accommodation Adjustment, especially the process by which the eye adjusts itself to focus on near objects At rest, the eye is focused for distant vision, when its lens is thin and flat To make focusing on a nearer object possible, the ciliary muscle of the eye contracts, which reduces the pull on the outer rim of the lens, allowing it to become thicker and more convex With age, the lens loses its elasticity This makes accommodation more and ACCOMMODATION Light rays from near object Ciliary muscle Point of focus NEAR FOCUS Light rays from distant object Rounded lens bends the light Ciliary muscle Point of focus DISTANT FOCUS Flattened lens A A ACETYLCYSTEINE ACID–BASE BALANCE Drugs such as donepezil and rivastigmine work by blocking the action of acetylcholinesterase, the enzyme in the brain responsible for the breakdown of acetylcholine This raises acetylcholine levels, and, in half of all patients, the drugs slow the rate of progression of dementia They have no effect on dementia due to other causes, such as stroke or head injury, however Common side effects include nausea, dizziness, and headache Rarely, difficulty in passing urine may occur acetylcysteine A drug used in the treatment of paracetamol overdose and as a mucolytic drug to loosen sputum When the drug is taken in large doses, vomiting or rash may occur as rare side effects achalasia A rare condition of unknown cause in which the muscles at the lower end of the oesophagus and the sphincter (valve) between the oesophagus and the stomach fail to relax to let food into the stomach after swallowing As a result, the lowest part of the oesophagus is narrowed and becomes blocked with food, while the part above widens Symptoms include difficulty and pain with swallowing and pain in the lower chest and upper abdomen A barium swallow (a type of barium X-ray examination) and gastroscopy may be performed to investigate achalasia ACHILLES TENDON Violent stretching of the tendon can cause it to rupture; in such cases, surgical repair may be necessary achlorhydria Absence of stomach acid secretions This may be due to chronic atrophic gastritis or to an absence or malfunction of acid-producing parietal cells in the stomach lining Achlorhydria may not produce symptoms but is associated with stomach cancer, however, and is a feature of pernicious anaemia (see anaemia, megaloblastic) achondroplasia A rare genetic disorder of bone growth that leads to short stature The condition is caused by a dominant gene (see genetic disorders) but often arises as a new mutation The long bones of the arms and legs are affected mainly The cartilage that links each bone to its epiphysis (the growing area at its tip) is converted to bone too early, preventing further limb growth Those affected have short limbs, a welldeveloped trunk, and a head of normal size except for a protruding forehead aciclovir An antiviral drug that can be taken by mouth, used topically, or given intravenously to reduce the severity of viral infections including herpes simplex and herpes zoster Local adverse reactions commonly occur after topical use Other side effects are uncommon but can include nausea and vomiting acid A substance defined as a donor of hydrogen ions (hydrogen atoms with positive electrical charges) Acid molecules, when mixed with or dissolved in water, split up to release their constituent ions; all acids release hydrogen as the positive ion (See also acid–base balance; alkali.) acid–base balance A combination of mechanisms that ensures that the body’s fluids are neither too acid nor too alkaline (alkalis are also called bases) The body has three mechanisms for maintaining normal acid–base balance: buffers, breathing, and the activities of the kidneys Buffers are substances in the blood that neutralize acid or alkaline wastes Rapid breathing results in the blood becoming less acidic; slow breathing has the opposite effect The kidneys regulate the amounts of acid or alkaline wastes in the urine Oesophageal dilatation allows the oesophagus to be widened for long periods Surgery to cut some of the muscles at the stomach entrance may be necessary Achilles Achilles tendon tendon The tendon that raises the heel The Achilles tendon is formed from the calf muscles (gastrocnemius, Heel soleus, and plantar muscles) and is attached to the calcaneus (heel-bone) Minor injuries to the Achilles tendon are common and can result in inflammation (tendinitis) Calf muscle ACIDOSIS ACOUSTIC NEUROMA Disturbances of the body’s acid–base balance result in either acidosis (excessive blood acidity) or alkalosis (excessive blood alkalinity) acidosis A disturbance of the body’s acid–base balance in which there is an accumulation of acid or loss of alkali (base) There are types of acidosis: metabolic and respiratory One form of metabolic acidosis is ketoacidosis, which occurs in uncontrolled diabetes mellitus and starvation Metabolic acidosis may also be caused by loss of bicarbonate (an alkali) as a result of severe diarrhoea In kidney failure, there is insufficient excretion of acid in the urine Respiratory acidosis occurs if breathing fails to remove enough carbon dioxide from the lungs The excess carbon dioxide remains in the bloodstream, where it dissolves to form carbonic acid Impaired breathing leading to respiratory acidosis may be due to chronic obstructive pulmonary disease (see pulmonary disease, chronic obstructive), bronchial asthma, or airway obstruction acid reflux Regurgitation of acidic fluid from the stomach into the oesophagus due to inefficiency of the muscular valve at the lower end of the oesophagus Also known as gastro-oesophageal reflux disease (GORD), acid reflux may inflame the oesophagus, resulting in heartburn due to oesophagitis It may occur in pregnancy and often affects overweight people acne A chronic skin disorder caused by inflammation of the hair follicles and sebaceous glands in the skin The most common type is acne vulgaris, which almost always develops during puberty Acne spots are caused by the obstruction of hair follicles by sebum (the oily substance secreted by the sebaceous glands) Bacteria multiply in the follicle, causing inflammation The change in sebum secretion at puberty seems to be linked with increased levels of androgen hormones (male sex hormones) Acne may be brought on or aggravated by drugs such as corticosteroids and androgens Exposure to certain chemicals and oils in the workplace can also cause a type of acne A Acne develops in areas of skin with a high concentration of sebaceous glands, mainly the face, centre of the chest, upper back, shoulders, and around the neck Milia (whiteheads), comedones (blackheads), nodACNE ules (firm swellings beneath the Sebaceous Inflamed skin skin), and cysts gland Plug (larger, fluid-filled Pus swellings) are the Hair most commonly occurring spots Some, particularly cysts, leave scars after they heal There is no instant cure for acne, but washing the affected areas at least twice daily may help to keep ACNE SPOT it under control Topical drug treatments, such as benzoyl peroxide or retinoic acid, unblock the pores and promote healing Ultraviolet light can be beneficial If topical treatment has failed, oral drug treatment with antibiotics, hormones, or isotretinoin may be given Acne improves slowly over time, often clearing up by the end of the teenage years acoustic nerve The part of the vestibulocochlear nerve (the 8th cranial nerve) that is concerned with hearing It is also known as the auditory nerve acoustic neuroma A rare, noncancerous tumour arising from supporting cells that surround the 8th cranial nerve (see acoustic nerve), usually within the internal auditory meatus (the canal in the skull through which the nerve passes from the inner ear to the brain) Usually, the cause of an acoustic neuroma is unknown However, tumours that affect the nerves on both sides of the head simultaneously may be part of a condition known as neurofibromatosis Acoustic neuroma can cause deafness, tinnitus, loss of balance, and pain in the face and the affected ear Diagnosis is made by hearing tests followed by X-rays, CT scanning, or MRI Surgery may be needed, but treatment A ACROCYANOSIS ACTINOMYCOSIS with radiotherapy to shrink the tumour is also effective acrocyanosis A circulatory disorder in which the hands and feet turn blue, may become cold, and sweat excessively Acrocyanosis is caused by spasm of the small blood vessels and is often aggravated by cold weather It is related to Raynaud’s disease acrodermatitis enteropathica A rare inherited disorder in which areas of the skin (most commonly the fingers, toes, scalp, and the areas around the anus and mouth) are reddened, ulcerated, and covered with pustules Acrodermatitis enteropathica is due to an inability to absorb enough zinc from food Zinc supplements usually help acromegaly A rare disease characterized by abnormal enlargement of the skull, jaw, hands, feet, and also of the internal organs It is caused by excessive secretion of growth hormone from the anterior pituitary gland at the base of the brain and is the result of a pituitary tumour A tumour that develops before puberty results in gigantism Acromegaly is diagnosed by measuring blood levels of growth hormone, followed by CT scanning or MRI acromioclavicular joint The joint that lies between the outer end of the clavicle (collarbone) and the acromion (the bony prominence at the top of the scapula (shoulderblade) acroparaesthesia A medical term used to describe tingling in the fingers or toes (see pins-and-needles) ACTH The common abbreviation for adrenocorticotrophic hormone (also called corticotrophin) ACTH is produced by the anterior pituitary gland and stimulates the adrenal cortex (outer layer of the adrenal glands) to release various corticosteroid hormones, most importantly hydrocortisone (cortisol) but also aldosterone and androgen hormones ACTH production is controlled by a feedback mechanism involving both the hypothalamus and the level of hydrocortisone in the blood ACTH levels increase in response to stress, emotion, injury, infection, burns, surgery, and decreased blood pressure A tumour of the pituitary gland can cause excessive ACTH production which leads to overproduction of hydrocortisone by the adrenal cortex, resulting in Cushing’s syndrome Insufficient ACTH production results in decreased production of hydrocortisone, causing low blood pressure Synthetic ACTH is occasionally given by injection to treat arthritis or allergy actin A protein involved in muscle contraction, in which microscopic filaments of actin and another protein, myosin, slide in between each other acting out Impulsive actions that may reflect unconscious wishes The term is most often used by psychotherapists to describe behaviour during analysis when the patient “acts out” rather than reports fantasies, wishes, or beliefs Acting out can also occur as a reaction to frustrations encountered in everyday life, often taking the form of antisocial, aggressive behaviour actinic Pertaining to changes caused by the ultraviolet rays in sunlight, as in actinic dermatitis (inflammation of the skin) and actinic keratosis (roughness and thickening of the skin) actinomycosis An infection caused by ACTINOMYCES ISRAELII or related actinomycete bacteria The most common form of actinomycosis affects the jaw area A painful swelling appears and pus discharges through small openings that develop in the skin Another form ACROMIOCLAVICULAR JOINT Clavicle Acromioclavicular joint Acromion Scapula Humerus acromion A bony prominence at the top of the scapula (shoulderblade) The acromion articulates with the end of the clavicle (collarbone) to form the acromioclavicular joint 10 ACUITY, VISUAL ADENOCARCINOMA of actinomycosis affects the pelvis in women, causing lower abdominal pain and bleeding between periods This form was associated with a type of IUD, no longer in use, that did not contain copper Rarely, forms of the disorder affect the appendix or lung Actinomycosis is treated with antibiotics acuity, visual See visual acuity acupressure A derivative of acupuncture in which pressure is applied instead of needles acupuncture A branch of Chinese medicine in which needles are inserted into a patient’s skin as therapy for various disorders or to induce anaesthesia Traditional Chinese medicine maintains that the chi (life-force) flows through the body along channels called meridians A blockage in one or more of these meridians is thought to cause ill health Acupuncturists aim to restore health by inserting needles at appropriate sites along the affected meridians The needles are stimulated by rotation or by an electric current Acupuncture has been used successfully as an anaesthetic for surgical procedures and to provide pain relief after operations and for chronic conditions acute A term often used to describe a disorder or symptom that develops suddenly Acute conditions may or may not be severe, and they are usually of short duration (See also chronic.) Adam’s apple A projection at the front of the neck, just beneath the skin, that is formed by a prominence on the thyroid cartilage, which is part of the larynx (voice box) The Adam’s apple enlarges in males at puberty ADD The abbreviation for attention deficit disorder, more commonly known as the corticosteroid hormones hydrocortisone and aldosterone, normally produced by the adrenal cortex (the outer part of the adrenal glands) Excessive amounts of ACTH are secreted by the pituitary gland in an attempt to increase output of the corticosteroid hormones Secretion and activity of another hormone, melanocyte stimulating hormone (MSH), is also increased Addison’s disease can be caused by any disease that destroys the adrenal cortices The most common cause is an autoimmune disorder in which the immune system produces antibodies that attack the adrenal glands Symptoms generally develop gradually over months or years, and include tiredness, weakness, abdominal pain, and weight loss Excess MSH may cause darkening of the skin in the creases of the palms, pressure areas of the body, and the mouth Acute episodes, called Addisonian crises, brought on by infection, injury, or other stresses, can also occur The symptoms of these include extreme muscle weakness, dehydration, hypotension (low blood pressure), confusion, and coma Hypoglycaemia (low blood glucose) also occurs Life-long corticosteroid drug treatment is needed Treatment of Addisonian crises involves rapid infusion of saline and glucose, and supplementary doses of corticosteroid hormones adduction Movement of a limb towards the central line of the body, or of a digit towards the axis of a limb Muscles that carry out this movement are often called adductors (See also abduction.) adenitis Inflammation of lymph nodes Cervical adenitis (swelling and tenderness of the lymph nodes in the neck) occurs in certain bacterial infections, especially tonsillitis, and glandular fever (see infectious mononucleosis) Mesenteric lymphadenitis is inflammation of the lymph nodes inside the abdomen and is usually caused by viral infection Treatment of adenitis may include analgesic drugs, and antibiotic drugs if there is a bacterial infection adenocarcinoma The technical name for a cancer of a gland or glandular tissue, or for a cancer in which the cells attention deficit hyperactivity disorder addiction Dependence on, and craving for, a particular drug, for example alcohol, diazepam (a tranquillizer), or heroin Reducing or stopping intake of the drug may lead to characteristic physiological or psychological symptoms (see withdrawal syndrome), such as tremor or anxiety (See also alcohol dependence; drug dependence.) Addison’s disease A rare chronic disorder in which there is a deficiency of 11 A WATER INTOXICATION WEIGHT due to emotion, conjunctival or corneal irritation, or an obstruction to the channel that drains tears from the eye (See also lacrimal apparatus.) water intoxication A condition that is caused by excessive water retention in the brain The principal symptoms are headaches, dizziness, nausea, confusion, and, in severe cases, seizures and unconsciousness Various disorders can disrupt the water balance in the body, leading to accumulation of water in the tissues Examples include kidney failure, liver cirrhosis, severe heart failure, diseases of the adrenal glands, and certain lung or ovarian tumours producing a substance similar to ADH (antidiuretic hormone) Water intoxication is also seen in association with the use of Ecstasy (MDMA), during which excessive amounts of water are drunk There is also a risk of water intoxication after surgery, caused by increased ADH production water on the brain A nonmedical term for hydrocephalus water on the knee A popular term for accumulation of fluid within or around the knee joint The most common cause is bursitis (See also effusion, joint) water retention Accumulation of fluid in body tissues (see oedema) water tablets A nonmedical term for diuretic drugs wax bath A type of heat treatment in which hot liquid wax is applied to a part of the body to relieve pain and stiffness in inflamed or injured joints Wax baths may be used to treat the hands of people with rheumatoid arthritis weakness A term used to describe a lack of vigour or strength This is a common symptom of a wide range of conditions, including anaemia, emotional problems, and various disorders affecting the heart, nervous system, bones, joints, and muscles When associated with emotional disorders, weakness may represent a lack of desire or ambition, rather than loss of muscle strength More specifically, the term describes loss of power in particular muscle groups, which may be accompanied by muscle wasting and loss of sensation (See also paralysis.) weal A raised bump on the skin that is paler than the adjacent tissue and which may be surrounded by an area of red inflammation Weals are characteristic of urticaria weaning The gradual substitution of solid foods for milk or milk formula in an infant’s diet (see feeding, infant) webbing A flap of skin, such as might occur between adjacent fingers or toes Webbing is a common congenital abnormality that often runs in families and which may affect or more digits Mild webbing is completely harmless, but surgical correction may be performed for cosmetic reasons In severe cases, adjacent digits may be completely fused (see syndactyly) Webbing of the neck is a feature of Turner’s syndrome Wegener’s granulomatosis A rare disorder in which granulomas (nodular collections of abnormal cells), associated with areas of chronic tissue inflammation due to vasculitis, develop in the nasal passages, lungs, and kidneys It is thought that the condition is an autoimmune disorder (in which the body’s natural defences attack its own tissues) Principal symptoms include a bloody nasal discharge, coughing (which sometimes produces bloodstained sputum), breathing difficulty, chest pain, and blood in the urine There may also be loss of appetite, weight loss, weakness, fatigue, and joint pains Treatment is with immunosuppressant drugs, such as cyclophosphamide or azathioprine, combined with corticosteroids to alleviate symptoms and attempt to bring about a remission With prompt treatment, most people recover completely within about a year, although kidney failure occasionally develops Without treatment, complications may occur, including perforation of the nasal septum, causing deformity of the nose; inflammation of the eyes; a rash, nodules, or ulcers on the skin; and damage to the heart muscle, which may be fatal weight The heaviness of a person or object In children, weight is routinely used as an index of growth In healthy adults, weight remains more or less stable as dietary energy intake matches energy expenditure (see metabolism) 595 W WEIGHT LOSS WEIGHT REDUCTION WEIGHT lb kg 210 95 200 90 190 85 180 WEIGHT 170 160 150 140 75 70 Healthy weight (BMI 20–25) 65 130 60 120 55 110 50 100 45 90 Overweight (BMI > 25) 80 Underweight (BMI < 20) 40 144 146 148 150 152 154 156 158 160 162 164 166 168170 172 174 176 178 180 182 184 186 188 190 192 194 cm 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 in HEIGHT WEIGHT ASSESSMENT CHART W Weight loss or weight gain occurs if the net balance is disturbed Weight can be compared with standardized charts for height, age, and sex At all ages, divergence from the normal weight for height may have medical implications For example, if weight is below 80 per cent of the standard weight for height, the individual’s nutrition is probably inadequate as a result of poor diet or disease, and if 20 per cent above the standard, he or she is considered to be suffering from obesity An alternative method of assessment is use of the body mass index (BMI, or Quetelet’s index), obtained by dividing weight in kilograms by the square of height in metres A healthy weight is 20–25 BMI; a BMI of greater than 25 indicates that a person is overweight weight loss This occurs any time there is a decrease in energy intake compared with energy expenditure The decrease may be due to deliberate weight reduction or a change in diet or activity level It may also be a symptom of a disorder Unexplained weight loss should always be investigated by a doctor Many diseases disrupt the appetite, which may lead to weight loss Depression reduces the motivation to eat, peptic ulcer causes pain and possible food avoidance, and some kidney disorders cause loss of appetite due to the effect of uraemia In anorexia nervosa and bulimia, complex psychological factors affect an individual’s eating pattern Digestive disorders, such as gastroenteritis, lead to weight loss through vomiting Cancer of the oesophagus (see oesophagus, cancer of) and stomach cancer cause loss of weight, as does malabsorption of nutrients in certain disorders of the intestine or pancreas Some disorders cause weight loss by increasing the rate of metabolic activity in cells Examples are any type of cancer, chronic infection such as tuberculosis, and hyperthyroidism Untreated diabetes mellitus also causes weight loss due to a number of factors weight reduction The process of losing excess body fat A person who is severely overweight (see obesity) is more at risk of various illnesses, such as diabetes mellitus, hypertension (high blood pressure), and heart disease The most efficient way to lose weight is to eat 500–1,000 kcal (2,100–4,200 kJ) a day less than the body’s total energy requirements Exercise also forms an extremely important part of a reducing regime, burning excess energy and improving muscle tone In most circumstances, drugs play little part in a weight loss programme 596 WEIL’S DISEASE WHIPLASH INJURY However, sibutramine and orlistat may be useful adjuncts to a reducing diet and may be appropriate for some people with a high BMI (see body mass index) Appetite suppressants related to amfetamines are not recommended Weil’s disease Another name for leptospirosis welder’s eye Acute conjunctivitis and keratopathy (corneal damage) caused by the intense ultraviolet light emitted by an electric welding arc Welder’s eye, which is also known as arc eye, results from the failure to wear adequate eye protection while welding wen A name for a sebaceous cyst Werdnig–Hoffmann disease A very rare inherited disorder of the nervous system that affects infants Also known as infantile spinal muscular atrophy, Werdnig–Hoffmann disease is a type of motor neuron disease, affecting the nerve cells in the spinal cord that control muscle movement Marked floppiness and paralysis occur during the first few months, and affected children rarely survive beyond age There is no cure for the disease Treatment aims to keep the affected infant as comfortable as possible Wernicke–Korsakoff syndrome An uncommon brain disorder almost always related to malnutrition occurring in chronic alcohol dependence, but occasionally due to that which occurs in other conditions, such as cancer Wernicke–Korsakoff syndrome is caused by deficiency of thiamine (see vitamin B complex), which affects the brain and nervous system The disease consists of stages: Wernicke’s encephalopathy and Korsakoff’s psychosis Wernicke’s encephalopathy usually develops suddenly and produces nystagmus (abnormal, jerky eye movements), ataxia (difficulty in coordinating body movements), slowness, and confusion Sufferers usually have signs of neuropathy, such as loss of sensation, pins-and-needles, or impaired reflexes The level of consciousness falls progressively and may lead to coma and death unless treated The condition is a medical emergency Treatment with high doses of intravenous thiamine often reverses most of the symptoms, sometimes within a few hours Korsakoff’s psychosis may follow Wernicke’s encephalopathy if treatment is not begun promptly enough Symptoms consist of severe amnesia, apathy, and disorientation Korsakoff’s psychosis is usually irreversible Wernicke’s area An area of the cerebral cortex in the brain that is involved in the interpretation of spoken and written language Wernicke’s encephalopathy See Wernicke–Korsakoff syndrome West Nile virus A virus transmitted from infected animals or birds to humnans by a mosquito bite In most cases, there are either no symptoms or a flu-like illness Rarely, a serious and potentially fatal illness, in which the virus infects the brain, can develop The virus is found in Africa, Eastern Europe, West Asia, the Middle East, and, since 1999, the East coast of the US wet dream Ejaculation that occurs during sleep See also nocturnal emission wheelchair A chair mounted on wheels used to provide mobility for a person unable to walk Manual wheelchairs are designed so that the hand-rims can be easily gripped by a disabled person They can also be pushed by a helper Powered wheelchairs use batteries and are controlled electronically by finger or chin pressure, or breath control wheeze A high-pitched, whistling sound produced in the chest during breathing, caused by narrowing of the airways It is a feature of asthma, bronchitis, bronchiolitis, and pulmonary oedema Inhalation of a foreign body may also be a cause (See also breathing difficulty.) whiplash injury An injury to the soft tissues, ligaments, and spinal joints of the neck caused by a forcible and violent bending of the neck backwards (hyperextension) and then forwards (flexion), or vice versa Such injury most commonly results from sudden acceleration or deceleration, as occurs in a car collision Damage to the spine usually involves minor sprain of a neck ligament, or subluxation (partial dislocation) of a cervical joint Occasionally, a ligament may rupture or a cervical vertebra may fracture 597 W WHIPPLE’S DISEASE WHITLOW WHIPLASH INJURY Cervical joint Cervical vertebra Ligaments Ligaments W BACKWARD FORCE (HYPEREXTENSION) FORWARD FORCE (FLEXION) (see spinal injury) Characteristically, pain and stiffness in the neck are much worse 24 hours after the injury Treatment may include immobilization in an orthopaedic collar, analgesic drugs, muscle-relaxant drugs, and physiotherapy It may take a few weeks before full pain-free movement is possible Whipple’s disease A rare disorder, also called intestinal lipodystrophy, that can affect many organs Symptoms include steatorrhoea as a result of malabsorption, abdominal pain, joint pains, progressive weight loss, swollen lymph nodes, anaemia, and fever The heart, lungs, and brain can also be affected The condition is most common in middle-aged men The cause is thought to be bacterial; affected tissues are found to contain macrophages (a type of scavenging cell) containing rod-shaped bacteria Treatment is with antibiotic drugs for at least year Dietary supplements are used to correct nutritional deficiencies occurring as a result of malabsorption Whipple’s operation A type of pancreatectomy in which the head of the pancreas and the loop of the duodenum are surgically removed whipworm infestation Small, cylindrical whip-like worms, 2.5–5 cm long, that live in the human large intestine Infestation occurs worldwide but is most common in the tropics Light infestation causes no symptoms; heavy infestation can cause abdominal pain, diarrhoea, and, sometimes, anaemia, since a small amount of the host’s blood is consumed every day Diagnosis is through the identification of whipworm eggs in the faeces Treatment is with anthelmintic drugs, such as mebendazole A heavy infestation may require more than course of treatment whitehead A very common type of skin blemish (see milia) white matter Tissue in the nervous system composed of nerve fibres (axons) White matter makes up the bulk of the cerebrum (the large hemispheres of the brain) and continues down into the spinal cord; its main role is to transmit nerve impulses (See also grey matter.) WHITE MATTER White matter Cerebrum Grey matter Brain stem Cerebellum Spinal cord SECTION THROUGH BRAIN whitlow An abscess on the fingertip or toe, causing the finger to swell and become extremely painful and sensitive to pressure and touch It most commonly develops from acute paronychia A whitlow may be due to the virus that causes 598 WHO WITHDRAWAL SYNDROME herpes simplex or to a bacterial infec- to emerge fully from the gum as a result of overcrowding (see impaction, dental) witches’ milk A thin, white discharge from the nipple of a newborn infant, caused by maternal hormones that entered the fetus’s circulation through the placenta Witches’ milk occurs quite commonly It is usually accompanied by enlargement of or both of the baby’s breasts The condition is harmless and usually disappears spontaneously within a few weeks withdrawal The process of retreating from society and from relationships with others; usually indicated by aloofness, lack of interest in social activities, preoccupation with one’s own concerns, and difficulty in communicating The term is also applied to the psychological and physical symptoms that develop on discontinuing use of a substance on which a person is dependent (see withdrawal syndrome) withdrawal bleeding Vaginal blood loss that occurs when the body’s level of oestrogen or progesterone hormones or progestogen drugs drops suddenly The withdrawal bleeding that occurs at the end of each month’s supply of combined oral contraceptive pills mimics menstruation but is usually shorter and lighter Discontinuation of an oestrogenonly or progestogen-only preparation also produces bleeding, which may differ from normal menstruation in its amount and duration withdrawal method See coitus interruptus withdrawal syndrome Unpleasant mental and physical symptoms experienced when a person stops using a drug on which he or she is dependent (see drug dependence) Withdrawal syndrome most commonly occurs in those with alcohol dependence or dependence on opioids, in smokers, and in people addicted to tranquillizers, amfetamines, cocaine, marijuana, and caffeine Alcohol withdrawal symptoms start 6–8 hours after cessation of intake and may last up to days They include trembling of the hands, nausea, vomiting, sweating, cramps, anxiety, and, sometimes, seizures (See also confusion, delirium tremens, and hallucinations.) tion In some cases, it may be necessary to drain pus from the abscess WHO The commonly used abbreviation for the World Health Organization whooping cough See pertussis will, living See living will Wilms’ tumour A type of kidney cancer, also called nephroblastoma, that occurs mainly in children Wilson’s disease A rare, inherited disorder in which copper accumulates in the liver, resulting in conditions such as hepatitis and cirrhosis Copper is slowly released into other body parts, damaging the brain, causing mild intellectual impairment, and leading to debilitating rigidity, tremor, and dementia Symptoms usually appear in adolescence but can occur much earlier or later Lifelong treatment with penicillamine is needed and, if begun soon enough, can sometimes produce some improvement If the disease is discovered before the onset of symptoms, the drug may prevent them from developing wind A common name for gas in the gastrointestinal tract, which may be expelled through the mouth (see belching) or passed through the anus (see flatus) Babies often swallow air during feeding which, unless the baby is “winded”, can accumulate in the stomach and cause discomfort windpipe Another name for the trachea wiring of the jaws Immobilization of the jaws by means of metal wires to allow a fracture of the jaw to heal or as part of a treatment for obesity When a fracture is being treated, the jaws are kept wired in a fixed position for about weeks For promoting weight loss, the jaws are wired for as long as a year In both cases, the person is unable to chew and can take only a liquid or semi-liquid diet This form of diet treatment often fails because the person resumes previous eating habits following removal of the wires wisdom tooth One of the rearmost teeth, also known as 3rd molars The wisdom teeth normally erupt between the ages of 17 and 21, but in some people, or more fails to develop or erupt In many cases, wisdom teeth are unable 599 W WOBBLE BOARD WOUND Opioid withdrawal symptoms start after W notably smallpox, tuberculosis, and malaria Other functions include sponsoring medical research programmes, organizing a network of collaborating national laboratories, and providing expert advice and specific targets to its 160 member states with regard to health matters worm infestation Several types of worm, or their larvae, existing as parasites of humans They may live in the intestines, blood, lymphatic system, bile ducts, or in organs such as the liver In many cases, they cause few or no symptoms, but some can cause chronic illness There are main classes: roundworms and platyhelminths, which are subdivided into cestodes (tapeworms) and trematodes (flukes) Worm diseases found in developed countries include threadworm infestation, 8–12 hours and may last for 7–10 days Symptoms include restlessness, sweating, runny eyes and nose, yawning, diarrhoea, vomiting, abdominal cramps, dilated pupils, loss of appetite, irritability, weakness, tremor, and depression Withdrawal symptoms from barbiturate drugs and meprobamate start after 12–24 hours, beginning with tremor, anxiety, restlessness, and weakness, sometimes followed by delirium, hallucinations, and, occasionally, seizures A period of prolonged sleep occurs 3–8 days after onset Withdrawal from benzodiazepine drugs may begin much more slowly and can be life-threatening Withdrawal symptoms from nicotine develop gradually over 24–48 hours and include irritability, concentration problems, frustration, headaches, and anxiety Discontinuation of cocaine or amfetamines results in extreme tiredness, lethargy, and dizziness Cocaine withdrawal may also lead to tremor, severe depression, and sweating Withdrawal symptoms from marijuana include tremor, nausea, vomiting, diarrhoea, sweating, irritability, and sleep problems Caffeine withdrawal may lead to tiredness, headaches, and irritability Severe withdrawal syndromes require medical treatment Symptoms may be suppressed by giving the patient small quantities of the drug he or she had been taking More commonly, a substitute drug is given, such as methadone for opioid drugs or diazepam for alcohol The dose of the drug is then gradually reduced wobble board A balancing board used during physiotherapy to improve muscle strength and coordination in the feet, ankles, and legs A wobble board is sometimes used after an ankle sprain womb See uterus word blindness See alexia; dyslexia World Health Organization (WHO) An international organization established in 1948 as an agency of the United Nations with responsibilities for international health matters and public health The WHO headquarters are in Geneva, Switzerland The WHO has campaigned effectively against some infectious diseases, most ascariasis, whipworm infestation, toxocariasis, liver-fluke infestation, and various tapeworm infestations Those occurring in tropical regions include hookworm infestation, filariasis, guinea worm disease, and schistosomiasis WORM INFESTATION Threadworm egg Larva inside egg MICROSCOPIC VIEW OF WORM EGGS Worms may be acquired by eating undercooked, infected meat, by contact with soil or water containing worm larvae, or by accidental ingestion of worm eggs from soil contaminated by infected faeces Most infestations can be easily eradicated with anthelmintic drugs wound Any damage to the skin and/or underlying tissues caused by an accident, act of violence, or surgery Wounds in which the skin or mucous membrane is broken are called open; those in which they remain intact are termed closed 600 WOUND INFECTION WRY NECK Wounds can be divided into the following categories: an incised wound; an abrasion (or graze); a laceration; a penetrating wound; and a contusion wound infection Any type of wound is susceptible to the entry of bacteria; the resultant infection can delay healing, result in disability, and may even cause death Infection of a wound is indicated by redness, swelling, warmth, pain, and sometimes by the presence of pus or the formation of an abscess Infection may spread locally to adjacent organs or tissue, or to more distant parts of the body via the blood The type of infection depends upon how the wound occurred For example, wounds brought into contact with soil can result in tetanus STAPHYLOCOCCI, including MRSA, are also common wound infections Once infection is discovered, a sample of blood or pus is taken and the patient is given an antibiotic drug Any abscess should be drained surgically wrinkle A furrow in the skin Wrinkling is a natural feature of aging and is caused by a loss of skin elasticity Premature deep wrinkling is usually due to overexposure to the ultraviolet rays in sunlight, and to smoking No treatment can permanently restore skin elasticity, although some vitamin A derivatives are believed to reduce wrinkling A face-lift smoothes out wrinkles by stretching the skin, but the effects last only about years wrist The joint between the hand and the arm that allows the hand to be bent forward and backward relative to the arm and also to be moved side to side The wrist contains bones (known collectively as the carpus) arranged in rows, one articulating with the bones of the forearm, and the other connecting to the bones of the palm Tendons connect the forearm muscles to the fingers and thumb, and arteries and nerves supply the muscles, bones, and skin of the hand and fingers Wrist injuries may lead to serious disability by limiting hand movement A common injury in adults is Colles’ fracture, in which the lower end of the radius is fractured and the wrist and hand are WRIST Triquetrum Radius Lunate Ulna Scaphoid Trapezium Pisiform Trapezoid Hamate Capitate BONES OF WRIST displaced backwards In young children, similar displacement results from a fracture through the epiphysis (growing end) of the radius A sprain can affect ligaments at the wrist joint, but most wrist sprains are not severe (See also carpal tunnel syndrome; wrist-drop; tenosynovitis; and osteoarthritis.) wrist-drop Inability to straighten the wrist, so that the back of the hand can- not be brought into line with the back of the forearm This causes weakness of grip because the hand muscles can function efficiently only when the wrist is held straight Wrist-drop is caused by damage to the radial nerve, either by prolonged pressure in the armpit (see crutch palsy) or by fracture of the humerus (see humerus, fracture of) Treatment involves holding the wrist straight This may be achieved by means of a splint, but if damage to the radial nerve is permanent, the usual treatment is arthrodesis (surgical fusion) of the wrist bones in a straight position writer’s cramp See cramp, writer’s wry neck Abnormal tilting and twisting of the head It may be due to injury to, or spasm of, the muscles on one side of the neck (see torticollis), among other factors 601 W XANTHELASMA X-RAYS Noncancerous skin tumours and skin cancers also develop Xeroderma pigmentosum is often accompanied by related eye problems, such as photophobia and conjunctivitis Treatment of the condition consists of protecting the skin from sunlight Skin cancers are usually treated surgically or with radiotherapy xerophthalmia An eye disorder in which vitamin A deficiency causes the conjunctiva and cornea to become abnormally dry Without treatment, xerophthalmia may progress to keratomalacia, a condition in which severe damage is caused to the cornea xerostomia Abnormal dryness of the mouth, which can cause bad breath and may predispose the sufferer towards tooth decay (see caries, dental) Xerostomia is sometimes a symptom of Sjögren’s syndrome (See also mouth, dry.) xipamide A thiazide diuretic drug used to treat oedema (accumulation of fluid in tissues) and high blood pressure Side effects may include dizziness and mild gastrointestinal disturbances xiphisternum An alternative name for the xiphoid process, the small, leafshaped projection that forms the lowest of the parts of the sternum X-linked disorders Sex-linked genetic disorders in which the abnormal gene or genes (the causative factors) are located on the X chromosome Almost all affected people are males Haemophilia, fragile X syndrome and colour vision deficiency are examples X-rays A form of electromagnetic radiation of short wavelength and high energy X-rays are widely used in medicine for diagnosis and treatment because they can be used to image bones, organs, and internal tissues X-rays are produced artificially by bombarding a heavy metal tungsten target with electrons, in a device known as an X-ray tube Low doses of the X-rays that are emitted are passed through body tissue and form images on film or a fluorescent screen The X-ray image, also known as a radiograph or roentgenogram, shows the internal structure of the area that is being examined Dense structures, such as bone, absorb X X xanthelasma A yellowish deposit of fatty material that is visible in the skin around the eyes Xanthelasmas are common in elderly people and are usually of no more than cosmetic importance However, in younger people they may be associated with hyperlipidaemias, in which there is excess fat in the blood Xanthelasmas may be removed, if necessary, by a simple surgical procedure under a local anaesthetic Any associated hyperlipidaemia must also be treated (See also xanthomatosis.) xanthoma A yellowish deposit of fatty material in the skin, often on the elbow or buttock They may be associated with hyperlipidaemias (see xanthomatosis) xanthomatosis A condition in which deposits of yellowish, fatty material develop in various parts of the body, particularly in the skin, internal organs, corneas of the eyes, brain, and tendons The deposits may occur only in the eyelids (see xanthelasma) A key feature of xanthomatosis is the tendency for fatty material to be deposited in the linings of blood vessels, leading to generalized atherosclerosis Xanthomatosis is often associated with hyperlipidaemias Treatment aims to lower the levels of fats in the blood by means of a diet that is low in cholesterol and high in polyunsaturated fat, and by drug treatment X chromosome A sex chromosome, of which every normal female body cell has a pair Male body cells have X and Y chromosome; each sperm carries either an X or a Y chromosome Abnormal genes located on X chromosomes cause X-linked disorders xeroderma pigmentosum A rare, inherited skin disease The skin is normal at birth, but photosensitivity (extreme sensitivity to sunlight) causes it to become dry, wrinkled, freckled, and prematurely aged by about the age of 602 X-RAYS, DENTAL XYLOMETAZOLINE X-RAY Rib Spine Lung X-ray machine Adjustable stand Beam of X-rays Heart Diaphragm CHEST X-RAY IMAGE X-ray film in cassette CHEST X-RAY PROCEDURE produce high-quality images with the lowest possible radiation exposure to the patient The possibility of genetic damage can be minimized by using a lead shield to protect the patient’s reproductive organs from X-rays Radiographers and radiologists wear a film badge to monitor their exposure to radiation (See also imaging techniques; radiography; radiology.) X-rays, dental See dental X-rays xylitol A naturally occurring carbohydrate that is only partially absorbed by the body and is sometimes used as a sweetener by people with diabetes Xylitol chewing gum has been shown to reduce recurrent ear infections in some children Excess xylitol may lead to abdominal discomfort and flatulence xylometazoline A decongestant drug used in the form of a spray or drops to relieve nasal congestion caused by a common cold, sinusitis, or hay fever (see rhinitis, allergic) Xylometazoline is also used as an ingredient of eye-drops in the treatment of allergic conjunctivitis Excessive use of xylometazoline may cause headache, palpitations, or drowsiness Long-term use of the drug may cause nasal congestion to worsen when treatment is stopped X-rays well and appear white on an Xray image Soft tissues, such as muscle, absorb less and appear grey Because X-rays can damage living cells, especially those that are dividing rapidly, high doses of radiation are used for treating cancer (see radiotherapy) Hollow or fluid-filled parts of the body often not show up well on X-ray film unless they first have a contrast medium (a substance that is opaque to X-rays) introduced into them Contrastmedium X-ray techniques are used to image the gallbladder (see cholecystography), bile ducts (see cholangiography), the urinary tract (see urography), the gastrointestinal tract (see barium X-ray examinations), blood vessels (see angiography; venography), and the spinal cord (see myelography) X-rays can be used to obtain an image of a “slice” through an organ or part of the body by using a technique known as tomography More detailed images of a body slice are produced by combining tomography with the capabilities of a computer (see CT scanning) Large doses of X-rays can be extremely hazardous, and even small doses carry some risk (see radiation hazards) Modern X-ray film, equipment, and techniques 603 X YAWNING YELLOW FEVER and is absent in every female body cell Each sperm carries either a single X or a single Y chromosome Unlike the X chromosome, the Y chromosome carries little genetic material Its major function is to stimulate the development of the testes in the embryo There are no significant diseases related to abnormalities of the Y chromosome, but hairy ears is a trait thought to be determined by a Y-linked gene yeasts Types of fungi in which the body of the fungus comprises individual cells that occur either singly, in pairs, or in longer chains Certain yeasts can cause infections of the skin or mucous membranes; the most important of these disease-causing yeasts is CANDIDA ALBICANS, which causes candidiasis Y Y yawning An involuntary act, or reflex action, usually associated with drowsiness or boredom The mouth is opened wide and a slow, deep breath is taken through it in order to draw air into the lungs The air is then slowly released Yawning is accompanied by a momentary increase in the heart-rate, and, in many cases, watering of the eyes The purpose of yawning is unknown, but one theory suggests it is triggered by raised levels of carbon dioxide in the blood; thus, its purpose could be to reduce the level of carbon dioxide and increase that of oxygen in the blood yaws An infectious disease that tends to be found throughout poorer subtropical and tropical areas of the world Yaws is caused by a spirochaete (a spiral-shaped bacterium), and it spreads principally in conditions of poor hygiene The infection is almost always acquired in childhood, and it mainly affects the skin and bones The bacteria enter the body through abrasions in the skin Three or weeks after infection, an itchy, raspberry-like growth appears at the site of infection, sometimes preceded by fever and pains Scratching spreads the infection and causes more growths to develop elsewhere on the skin Without treatment, the growths heal slowly over the course of about months, but recurrence is common In about 10 per cent of untreated cases, widespread tissue loss eventually occurs This may eventually lead to gross destruction of the skin, bones, and joints of the legs, nose, palate and upper jaw Yaws can be cured by a single large dose of a penicillin drug given as an injection into muscle Y chromosome A sex chromosome that is present in every normal male body cell It is paired with an X chromosome YEASTS Nucleus Cytoplasm Cell wall Mitochondrion YEAST CELL yellow fever An infectious disease of short duration and variable severity that is caused by a virus transmitted by mosquitoes In severe cases, the skin yellows due to jaundice, from which the name yellow fever derives The infection may be spread from monkeys to humans in forest areas through various species of mosquito; and in urban areas it can be transmitted between humans by AEDES AEGYPTI mosquitoes Today, yellow fever is contracted only in Central America, parts of South America, and a large area of Africa Eradication of the causative mosquito from populated areas has greatly reduced its incidence Yellow fever is characterised by a sudden onset of fever and headache, often with nausea and nosebleeds and, despite the high fever, a very low heart-rate In 604 YERSINIA YTTRIUM yoga maintains flexibility of the body, teaches both physical and mental control, and is a useful relaxation technique If attempted by people in poor health, or practised incorrectly, yoga may pose certain health hazards, such as back disorders, hypertension (high blood pressure), and glaucoma (increased pressure in the eye) yolk sac The membranous sac, otherwise known as the vitelline sac, that lies against, and is attached to, the front of the embryo during the early stages of its existence During development, the sac decreases proportionately in size to the body, reducing finally to a narrow duct that passes through the umbilicus The yolk sac is believed to assist in the transportation of nutrients from the mother to the early embryo yttrium A very rare metal that, in its radioactive form, is sometimes used in cancer therapy and to treat joints affected by arthritis more serious cases, the fever is higher and there is severe headache and pain in the neck, back, and legs Damage may occur rapidly to the liver and kidneys, causing jaundice and kidney failure This may be followed by severe agitation and delirium, leading to coma and death Vaccination confers long-lasting immunity and should always be obtained before travel to affected areas A single injection of the vaccine gives protection for at least 10 years Reactions to the vaccine are rare and are usually trivial, although children under the age of should not be vaccinated During yellow fever epidemics, diagnosis is simple A diagnosis can be confirmed by carrying out blood tests to isolate the causative virus or to find antibodies to the virus No drug is effective against the yellow fever virus; treatment is directed at maintaining the blood volume Transfusion of fluids is often necessary Many patients recover in about days and, in mild to moderate cases, complications are few Relapses not occur and one attack confers lifelong immunity Overall, however, about 10 per cent of victims die yersinia A class of bacteria containing the organism responsible for the bubonic plague (YERSINIA PESTIS) In other forms, yersinia is responsible for a variety of infections, such as gastroenteritis, particularly in young children, and arthritis and septicaemia in adults yin and yang The opposing and interdependent principles that are fundamental to traditional Chinese medicine and philosophy Yin is associated with the female, darkness, coldness, and quiescence; yang embodies qualities of maleness, brightness, heat, and activity In a healthy body, yin and yang are in balance The concepts of yin and yang are also central to the theoretical basis of macrobiotics yoga A system of Hindu philosophy and physical discipline that is becoming increasingly popular throughout the world The main form of yoga that is practised in the West is hatha-yoga, in which the follower adopts a series of poses, called asanas, and uses a special breathing technique The practice of Y 605 ZIDOVUDINE ZOONOSIS Prolonged excessive intake of zinc may interfere with the intestinal absorption of iron and copper, leading to a deficiency of these minerals Zinc compounds, such as zinc oxide, are included in many preparations for treating skin and scalp disorders zinc oxide An ingredient of many skin preparations that has a mild astringent action and a soothing effect Zinc oxide is used to treat painful, itchy, or moist skin conditions and to ease the pain caused by haemorrhoids and insect bites or stings It also blocks the ultraviolet rays of the sun (see sunscreens) Zollinger–Ellison syndrome A rare condition characterized by severe and recurrent peptic ulcers in the stomach, duodenum, and jejunum (the 2nd part of the small intestine) Zollinger–Ellison syndrome is caused by or more tumours in the pancreas that secrete the hormone gastrin Gastrin stimulates production of large quantities of acid by the stomach, which leads to ulceration The high levels of acid in the digestive tract often also cause diarrhoea The tumours are cancerous, but of a slow-growing type If possible, they are removed surgically Proton pump inhibitor drugs are given to treat the ulcers zolpidem A drug used in the short-term treatment of insomnia Zolpidem has a brief duration of action and causes little hangover effect Side effects include diarrhoea, nausea, and dizziness zona pellucida The thick, transparent, noncellular layer that surrounds a developing egg cell in the ovarian follicle At fertilization, the zona pellucida is penetrated by at least sperm zoonosis Any infectious or parasitic disease of animals that can be transmitted to humans Unlike many disease organisms, zoonotic organisms are flexible and can adapt themselves to many different species Zoonoses are usually caught from animals closely associated with humans, either as pets, food sources, or scavenging parasites, such as rats Examples include toxocariasis, cat-scratch fever, some fungal infections, psittacosis, brucellosis, trichinosis, and leptospirosis Rabies can infect virtually any mammal, Z zidovudine An antiretroviral drug, formerly known as azidothymidine or AZT, that is used in combination with other antiretroviral drugs to slow the progression of AIDS The principal aim of antiretrovirals is to keep viral replication to as low a level as possible for as long as possible; they not constitute a cure Zidovudine was the first drug to be introduced to combat HIV infection Possible side effects of zidovudine include anaemia, which may be severe enough to require a blood transfusion, nausea, loss of appetite, and headache Zidovudine also impairs the absorption of trimethoprim and sulfamethoxazole, the antibiotic drugs used to treat pneumonia in people who have AIDS, thus reducing the effectiveness of these drugs ZIFT See zygote intrafallopian transfer zinc A trace element that is essential for normal growth, the development of the reproductive organs, normal functioning of the prostate gland, healing of wounds, and the manufacture of proteins and nucleic acids in the body Zinc also controls the activities of more than 100 enzymes and is involved in the functioning of the hormone insulin Particularly rich sources of zinc include lean meat, wholemeal breads, whole grain cereals, dried beans, and seafood Zinc deficiency is rare Most cases occur in people who are generally malnourished Deficiency may also be caused by any disorder that causes malabsorption; acrodermatitis enteropathica; or by increased zinc requirements due to cell damage (for example, as a result of a burn or in sickle cell anaemia) Symptoms of deficiency include impairment of taste and loss of appetite; there may also be hair loss and inflammation of the skin, mouth, tongue, and eyelids In children, zinc deficiency impairs growth and delays sexual development 606 ZOPICLONE ZYGOTE INTRAFALLOPIAN TRANSFER but dog bites are a common cause of human infection worldwide Other zoonoses are transmitted from animals less obviously associated with humans, usually by insect vectors For example, yellow fever is transmitted by mosquito bites (See also dogs, diseases ZYGOTE Zona pellucida Zygote from; cats, diseases from; rats, diseases from; insects and disease.) zopiclone A drug used in the short-term treatment of insomnia It has a brief dura- tion of action and causes little hangover effect Side effects include a bitter metallic taste, nausea, and dry mouth Z-plasty A technique that is used in plastic surgery to change the direction of a pre-existing scar so that it can be hidden in natural skin creases, or to relieve skin tension caused by the contracture of a scar Z-plasty is especially useful for revising unsightly scars on the face and for releasing scarring across those joints, such as on the fingers or in the armpits, that may restrict normal movement or cause deformity zygomatic arch The arch of bone, commonly known as the cheek bone, on either side of the skull just below the eye socket The zygomatic arch is formed of the zygomatic and temporal bones The zygote travels down of the woman’s fallopian tubes, dividing as it does so After about a week, the mass of cells (now called a blastocyst) implants into the lining of the uterus, and the next stage of embryological growth begins (See also embryo; fertilization.) zygote intrafallopian transfer A type of in vitro fertilization, also referred to as ZIFT, in which ova are fertilized outside the body and returned to a fallopian tube rather than to the uterus ZYGOMATIC ARCH Frontal bone Zygomatic bone Zygomatic arch Parietal bone Temporal bone Occipital bone Mandible zygote The cell that is produced when a sperm fertilizes an ovum A zygote, measuring about 0.1 mm in diameter in humans, contains all the genetic material for a new individual The zygote is surrounded by a protein-rich layer known as the zona pellucida 607 ACKNOWLEDGMENTS PICTURE CREDITS Dr D.A.Burns: 374bcl, 469tr; Professor Terry Hamblin, The Royal Bournemouth Hospital Medical Illustration Department: 456cr; Dr N R Patel: 185cr; Science Photo Library: 600bcr; Biophoto Associates 506bl; CNRI 129cr, 250bl; Dr P Marazzi 67bl, 218br; Eye of Science 284bcr; John Radcliffe Hospital 293tr; National Institute of Health 444br; Professor P Motta/Department of Anatomy/University "La Sapienza", Rome 423br; National Meningitis Trust: 252cl; St John's Institute of Dermatology: 302br, 361bcr; The Wellcome Institute Library, London: 255cr, 257cl, 325bcl All other images copyright © Dorling Kindersley For further information see: www.dkimages.com ILLUSTRATORS Evi Antoniou, Joanna Cameron, Mick Gillah, Tony Graham, Mark Iley, Deborah Maizels, Patrick Mulrey, Peter Ruane, Richard Tibbitts, Halli Verrinder, Philip Wilson, Deborah Woodward, PHOTOGRAPHERS Andy Crawford, Steve Gorton, Gary Ombler, Tim Ridley, Spike Walker (microphotography) Every effort has been made to acknowledge those individuals, organizations, and corporations that have helped with this book and to trace copyright holders DK apologizes in advance if any omission has occurred If an omission does come to light, the company will be pleased to insert the appropriate acknowledgment in any subsequent editions of this book 608 The British Medical Association ILLUSTRATED MEDICAL DICTIONARY The only full-colour illustrated dictionary that provides authoritative yet accessible definitions of every important medical term A–Z quick-reference guide to over 5,500 medical terms • Approximately 400 full-colour images • Comprehensive coverage, including anatomical terms, disorders, tests, treatments and drugs • Expanded definitions for fuller understanding • Extensive cross-referencing for fast access to related topics • Illustrations labelled to show key features see our complete catalogue at www.dk.com £12.99 ... types of anaesthesia are used: local (see anaesthesia, local) and general (see anaesthesia, general) Damage to nerve tissues by injury or disease can produce anaesthesia in a localized area anaesthesia,... ion (See also acid–base balance; alkali.) acid–base balance A combination of mechanisms that ensures that the body’s fluids are neither too acid nor too alkaline (alkalis are also called bases)... the stomach lining Achlorhydria may not produce symptoms but is associated with stomach cancer, however, and is a feature of pernicious anaemia (see anaemia, megaloblastic) achondroplasia A rare