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, 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 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 hotwater 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 6 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. 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 bone-like 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 staphylo- cocci, are the usual cause of abscesses, 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 spon- taneously. 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. An abscess in a periodontal pocket can usually be treated by the dentist scrap- ing 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 A drug that is used to treat type 2 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 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. 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. Com- mon 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.
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 tendon The tendon that raises the heel. The Achilles tendon is formed from the calf muscles (gastrocnemius, soleus, and plantar muscles) and is attached to the 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 molec- ules, when mixed with or dissolved in water, split up to release their con- stituent 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. calcaneus (heel-bone). 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 2 types of acidosis: metabolic and respiratory. One form of metabolic acidosis is ketoacidosis, which occurs in uncon- trolled 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 obstruc- tion 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 chemi- cals and oils in the workplace can also cause a type of acne.
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), nodules (firm swel- lings beneath the skin), and cysts (larger, fluid-filled swellings) are the 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 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 anti- biotics, 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 vestibelocochlear 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 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 aggra- vated 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 secre- tion 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. Acromeg- aly 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 cla- vicle (collarbone) and the acromion (the bony prominence at the top of the scapula (shoulderblade).
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.
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 con- traction, 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 thanreports 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 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 anaes- thetic 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 attention deficit hyperactivity disorder.
Addiction Dependence on, and craving for, a particular drug, for example alco- hol, 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 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 tender- ness 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 form gland-like structures. An adenocarcinoma arises from epithelium (the layer of cells that lines the inside of organs). Cancers of the colon, breast, pancreas, and kidney are usually adenocarcinomas, as are some cancers of the cervix, oesophagus, salivary glands, and other organs. (See also intestine, cancer of; kidney cancer; pancreas, cancer of.)
Adenoidectomy Surgical removal of the adenoids. An adenoidectomy is usually performed on a child with abnormally large adenoids that are causing recurrent infections of the middle ear or air sinuses. The operation may be performed together with tonsillectomy.
Adenoids A mass of glandular tissue at the back of the nasal passage above the tonsils. The adenoids are made up of lymph nodes, which form part of the body’s defences against upper respiratory tract infections; they tend to enlarge during early childhood, a time when such infections are common.
Imost children, adenoids shrink after the age of about 5 years, disappearing altogether by puberty. In some children, however, they enlarge, obstructing breathing and blocking the eustachian tubes, which connect the middle ear to the throat. This results in recurrent infections and deafness. Infections usu- ally respond to antibiotic drugs, but if they recur frequently, adenoidectomy may be recommended.
Adenoma A noncancerous tumour or cyst that resembles glandular tissue and arises from the epithelium (the layer of cells that lines the inside of organs). Adenomas of endocrine glands can cause excessive hormone produc- tion, leading to disease. For example, pituitary gland adenomas can result in acromegaly or Cushing’s syndrome.
Adenomatosis An abnormal condition of glands in which they are affected either by hyperplasia (overgrowth) or the development of numerous adenomas (noncancerous tumours). Adenomatosis may simultaneously affect 2 or more different endocrine glands.
ADH The abbreviation for antidiuretic hormone (also called vasopressin), which is released from the posterior part of the pituitary gland and acts on the kidneys to increase their reabsorption of water into the blood. ADH reduces the amount of water lost in the urine and helps to control the body’s overall water balance. ADH production is controlled by the hypothalamus. Various factors can affect ADH production and thus disturb the body’s water balance, including drinking alcohol, the disorder diabetes insipidus, or a major operation.
ADHD The abbreviation for attention deficit hyperactivity disorder.
Adhesion The joining of normally unconnected body parts by bands of fibrous tissue. Adhesions are sometimes present from birth, but they most often develop as a result of scarring after inflammation. Adhesions are most common in the abdomen, where they often form after peritonitis (inflammation of the abdominal lining) or surgery. Sometimes, loops of intestine are bound together by adhesions, causing intestinal obstruction (see intestine, obstruction of). In such cases, surgery is usually required to cut the bands of tissue.
Adipose tissue A layer of fat just beneath the skin and around various internal organs. Adipose tissue is built up from fat deposited as a result of excess food intake, thus acting as an energy store; excessive amounts of adipose tissue produce obesity. The tissue insulates against loss of body heat and helps absorb shock in areas subject to sudden or frequent pressure, such as the buttocks of feet. In men, superficial adipose tissue accu- mulates around the shoulders, waist, and abdomen; in women, it occurs on the breasts, hips, and thighs
Adjuvant A substance that enhances the action of another substance in the body. The term is usually used to describe an ingredient added to a vaccine to increase the production of antibodies by the immune system, thus enhancing the vaccine’s effect. Adjuvant chemotherapy is the use of anticancer drugs in addition to surgical removal of a tumour.
Adlerian theory The psychoanalytical ideas set forth by the Austrian psychia- trist Alfred Adler. Also called individual psychology, Adler’s theories were based on the idea that everyone is born with feelings of inferiority. Life is seen as a constant struggle to overcome these feelings; failure to do so leads to neurosis. (See also psychoanalytic theory.)
Adolescence The period between child- hood and adulthood, which broadly corresponds to the teenage years. Adolescence commences and overlaps with, but is not the same as, puberty. ADP The abbreviation for adenosine diphosphate, the chemical that takes up energy released during biochemical reactions to form ATP (adenosine triphos-phate), the body’s main energy-carrying chemical. When ATP releases its energy, ADP is reformed. (See also metabolism.)
Adrenal failure Insufficient production of hormones by the adrenal cortex (the outer part of the adrenal glands). It can be acute or chronic. Adrenal failure may be acute or chronic. Adrenal failure may be caused by a disorder of the adrenal glands, in which case it is called Addi-son’s disease, or by reduced stimulation of the adrenal cortex by ACTH, a hor-mone produced by the pituitary gland.
Adrenal glands A pair of small, trian-gular endocrine glands located above the kidneys. Each adrenal gland has 2 distinct parts: the outer cortex and the smaller, inner medulla. The cortex secretes aldosterone, which, smaller, inner medulla. The cortex secretes aldosterone, which, together with hydrocortisone and corticosterone and small amounts of androgen hormones helps to maintain blood pressure. Hydrocortisone controls the body’s use of fats, proteins, and car-bohydrates and is also important in helping the body to cope with stress. Hydrocortisone and corticosterone also suppress inflammatory reactions and some activities of the immune system. Production of adrenal cortical hor- mones is controlled by ACTH, which is produced in the pituitary gland. The adrenal medulla is part of the sympathetic autonomic nervous system. In response to stress, it secretes the hormones adrenaline (epinephrine) and noradrenaline (norepinephrine), which increase heart-rate and blood flow.