A

A

A–B ratio used in pregnancy ultrasound scans to assess the amount of blood through the umbilical cord; a low ratio is normal, a high ratio may indicate intrauterine growth retardation.

abdomen the largest body cavity.

abdominal associated with the abdomen.

abdominal aorta that part of the aorta within the abdomen. Smaller arteries branch from it to supply oxygenated blood to abdominal structures, for example, kidneys.

abdominal aortic aneurysm (AAA) a swelling in the abdominal aorta. See also aneurysm.

abdominal breathing more than usual use of the diaphragm and abdominal muscles to increase the input of air to, and output from, the lungs. It can be done voluntarily. When it occurs in disease it is a compensatory mechanism for inadequate oxygenation.

abdominal cavity that area below the diaphragm; the abdomen (see figure on p. 2).

abdominal excision (of the rectum) an operation sometimes performed for rectal cancer. The rectum is mobilized via an abdominal approach. The bowel is divided well proximal to the cancer. The proximal end is brought out as a permanent colostomy. Excision of the distal bowel, containing the cancer and the anal canal, is completed through a perineal incision.

abdominal reflex a superficial reflex where the abdominal muscles contract when the skin is lightly stroked.

abdominal regions where the surface anatomy is divided into nine regions; used to describe the location of organs or symptoms, such as pain.

abdominal thrust (Heimlich’s manoeuvre) a technique for removing foreign matter from the trachea of a choking person. Performed by holding the patient from behind and jerking the operator’s clenched fist into the victim’s epigastrium. Do not practice on volunteers.

abdominopelvic associated with the abdomen and pelvis or pelvic cavity.

abdominoperineal associated with the abdomen and perineum.

abdominoplasty (tummy tuck) plastic surgical procedure used to tighten the abdominal muscles.

abducens nerve the sixth pair of cranial nerves. They control the lateral rectus muscle of the eyeball, which turns the eyeball outwards.

abduct to draw away from the median line of the body. See also adduct.

abduction the act of moving, (or abducting) away from the midline. See also adduction.

abductor a muscle which, on contraction, draws a part away from the median line of the body. See also adductor.

aberrant abnormal; usually applied to a blood vessel or nerve which does not follow the normal course.

aberration a deviation from normal. See also chromosomal aberration, optical aberration.

ablation amputation, excision of part of the body or the removal of a growth or harmful substance.

abort to terminate before full development.

abortion abrupt termination of a process. The induced expulsion from the uterus of the product of conception before viability by medical or surgical means. N.B. The preferred term for unintentional loss of the product of conception prior to 24 weeks’ gestation is miscarriage. criminal abortion intentional evacuation of the uterus by other than trained licensed personnel, or where abortion is prohibited by law.

abrasion superficial injury to skin or mucous membrane from scraping or rubbing (excoriation). Can be used therapeutically for removal of scar tissue (dermabrasion).

abscess localized collection of pus. May be acute or chronic. Brodie’s abscess chronic osteomyelitis occurring without previous acute phase. In dentistry a common site is the apex of the root of a tooth.

absolute detector efficiency the ability of a detector to measure the total events emitted by a source of ionizing radiation.

absorbed when a photon interacts with an object and as a result loses all its energy.

absorbed dose is the measure of the amount of radiation absorbed by an object.

absorbed fraction the quantity of radiation absorbed by the tissues in radionuclide imaging.

absorption in intensifying screens the incident photons are absorbed by the phosphor, 95% as a result of the photoelectric effect and 5% by the Compton effect. See also photoelectric effect, Compton effect.

absorption rate constant a value describing the amount of a drug absorbed in a unit of time.

abuse misuse of equipment, drugs and other substances, power and position. Deliberate injury to another person. It may be either physical, sexual, psychological or through neglect, such as failure to feed or keep clean. The term can apply to any group of individuals, especially those most vulnerable such as children, older people, and those with mental health problems or learning disabilities. See also child abuse, elder abuse.

accelerated fractionation in radiotherapy it is the method of delivering small doses of radiation several times a day, over a reduced number of days compared with a standard course of treatment.

accelerating voltage the kVp determining the minimum wavelength in the spectrum, in a constant potential unit it will be present throughout the exposure.

acceleration change in velocity in unit time, unit metre/second/second.

accelerator a chemical that controls activity by assuring the correct pH values are maintained; in developer sodium or potassium hydroxide is used.

acceptance tests tests done on newly installed radiotherapy equipment and include checking that the agreed specification has been met with regard to the radiotherapy beam, movement of the tube stand, electrical aspects, radiation safety requirements and accessories.

accessory motion sliding, gliding or rolling motion that occurs within and between joint surfaces during active or passive joint movement.

access time the time taken for the computer to get information from a storage device, e.g. disk or tape.

Access to Health Records Act (1990) allows access to both paper and computerized health records made after 1991, with certain exceptions, such as where they may cause serious physical or mental harm to a person.

acclimatization the body’s ability to adapt physiologically to a variation in environment such as climate or altitude.

accommodation ability of the lens of the eye to increase its refractive power in order to focus on near objects. Decreased sensitivity to stimuli demonstrated by neurons that have been exposed to subthreshold stimuli for long periods of time.

accommodation reflex constriction of the pupils and convergence of the eyes for near vision.

accountability health professionals have a duty to care according to law. In some countries the statutory body, and/or the professional organization, develop a code of conduct via which each practitioner can accept responsibility and accountability for the professional service delivered to each patient/client. See also duty of care, malpractice, negligence.

accretion an increase of substance or deposit round a central object.

accuracy the ability of a detector to correctly indicate dose.

ACE inhibitors angiotensin-converting enzyme inhibitors allow blood vessels to dilate by preventing the formation of angiotensin II, an artery constrictor. Used in the treatment of heart failure, hypotension, diabetic nephropathy and post-myocardial infarction.

acephalous without a head.

acetabuloplasty an operation to improve the depth and shape of the hip socket (acetabulum); necessary in such conditions as developmental dysplasia of the hip and osteoarthritis of the hip.

acetabulum a cup-like socket on the external lateral surface of the pelvis into which the head of the femur fits to form the hip joint.

acetic acid present as the acid in fixing solutions and is used in combination with aluminium chloride as the hardener.

acetoacetate an acidic ketone produced during an interim stage of fat oxidation in the body. Some can be utilized as a fuel by tissues, such as the kidney. In situations where carbohydrate molecules are not available for metabolism, such as in diabetes mellitus or starvation, excess is produced and the high levels in the blood result in ketoacidosis with severe disturbances of pH, fluid and electrolytes.

acetonuria acetone and other ketones in the urine. See also ketonuria.

achalasia an abnormal condition where the muscles are unable to relax, particularly the lower oesophageal sphincter.

Achilles tendinitis inflammation of the Achilles tendon.

Achilles tendon the tendinous termination of the soleus and gastrocnemius muscles inserted into the heel bone (os calcis or calcaneus).

acholia the absence of bile.

acholuria the absence of bile pigments from the urine. See also jaundice.

achondroplasia without cartilage. A disorder of the growth of cartilage in the epiphyses of the long bones and skull.

acid any substance that has an excess of hydrogen ions over hydroxyl ions, for example, hydrochloric acid. They have a pH below 7 and turn blue litmus red and react with alkalis to form salts plus water. The chemical in the fixer solution that neutralizes the alkaline developer as soon as the film reaches the fixing tank and therefore prevents further development, the acid used is either acetic acid or sulphuric acid and depends on the hardener used.

acidaemia a high level of acid (hydrogen ions) in the blood resulting in a below normal blood pH < 7.35 (hydrogen ion concentration >44mmol/L). See also acidosis.

acid–base balance equilibrium between the acid and base elements of the blood and body fluids.

acidity the state of being acid or sour. The degree of acidity can be measured on the pH scale where a pH below 7 is acid and pH 6 denotes a weak acid and pH 1 a strong acid.

acidosis process leading to the accumulation of excess acid in the body. respiratory acidosis due to hypoventilation and the accumulation of carbon dioxide. metabolic acidosis due to the generation of excess acid (lactic acidosis) or depletion of alkali (for example, diarrhoea). See also acidaemia.

acid phosphatase an enzyme which synthesizes phosphate esters of carbohydrates in an acid medium. An increase of this enzyme in the blood is indicative of cancer of the prostate gland.

Acinetobacter a genus of Gram-negative aerobic bacteria causing infections that include wound infection, pneumonia and meningitis. The microorganism has developed antibiotic resistance and is a particular danger to critically ill patients having intensive or high-dependency care.

acini minute saccules or alveoli, lined or filled with secreting cells. Several acini combine to form a lobule.

acoustic sound or hearing.

acoustic cavitation a potential biological effect of ultrasound imaging, marked by large amplitude oscillations of microscopic gas bubbles.

acoustic enhancement an artefact that occurs in ultrasound imaging when an object with a low level of absorption causes objects which are further away from the probe to be brighter than they should be.

acoustic impedance a value given to a substance and is calculated by multiplying the density of the medium by the velocity of the ultrasound travelling through the medium and is independent of frequency.

acoustic neuroma a benign tumour (schwannoma) affecting the eighth cranial nerve (vestibulocochlear nerve) as it passes through the skull into the brainstem, causing problems in hearing and balance.

acoustic shadow in ultrasound imaging, the absence of echoes produced by a dense structure such as a calculus which prevents the transmission of ultrasound waves by reflection.

acoustic shadowing tissues which reflect or absorb ultrasound, for example, gall stones, will cast a shadow on the image. The tissue interface has to be similar to or larger than the ultrasound beam to cause shadowing.

acoustic window an area of the body used to allow imaging of underlying structures, for example, the spaces between the ribs, the liver.

acquired immune deficiency syndrome (AIDS) a term used to denote a particular stage of infection with human immunodeficiency virus (HIV). The Centers for Disease Control and Prevention (CDC) define AIDS as the development of an AIDS-defining illness in a patient with HIV infection. A low CD4+ T cell count of less than 200 per mL (or less than 14% of lymphocytes) in an HIV-positive person is also regarded as AIDS-defining, regardless of symptoms or opportunistic infections.

acrocephalia (acrocephaly) a congenital malformation whereby the top of the head is pointed and the eyes protrude, due to premature closure of sagittal and coronal skull sutures.

acrocephalosyndactyly a congenital malformation consisting of a pointed top of head, with fusion of fingers and/or toes. See also Apert’s syndrome.

acrocyanosis coldness and blueness of the extremities due to circulatory disorder.

acrodynia acute, painful reddening of the extremities such as occurs in erythroedema polyneuropathy.

acromegaly enlargement of the hands, face, feet, and the bones of the head and chest occurring due to excess growth hormone in an adult, almost always from overactivity of the anterior lobe of the pituitary gland due to a pituitary adenoma.

acromicria smallness of the hands, face and feet.

acromioclavicular associated with the acromion process (of scapula) and the clavicle.

acromion the point or summit of the shoulder: the triangular process at the extreme outer end of the spine of the scapula.

acropacy thickening of the extremities.

acrosome structure surrounding the nucleus of a spermatozoon. It contains lytic enzymes which, when released by many spermatozoa (during the acrosome reaction), facilitate the penetration of an oocyte by a single spermatozoon.

actin one of the contractile proteins in a muscle myofibril; it reacts with myosin to cause contraction.

actinobiology study of the effects of radiation on living organisms.

action the activity or function of any part of the body.

action potential change in electrical potential and charge that occurs across excitable cell membranes during nerve impulse conduction or when muscles contract.

active energetic. active principle an ingredient which gives a complex drug its chief therapeutic value, for example, atropine is the active principle in belladonna. active range of motion the movement of a joint without assistance through a range of motion. Those produced by patients using their own neuromuscular mechanisms. See also immunity.

activators impurities which stimulate the phosphor of an intensifying screen to emit light.

actual scores each score has a real value.

acuity clearness, sharpness, keenness. See also auditory acuity, visual acuity.

acute short and severe; not long drawn out or chronic.

acute abdomen a pathological condition within the abdomen requiring immediate surgical intervention.

acute coronary syndromes describes the spectrum of events ranging from the partial occlusion of a coronary artery resulting in unstable angina through to the complete occlusion of a coronary artery resulting in myocardial infarction.

acute dilatation of the stomach sudden enlargement of this organ due to paralysis of the muscular wall. See also paralytic ileus.

acute heart failure cessation or impairment of heart action, in previously undiagnosed heart disease, or in the course of another disease.

acute injury an injury that presents with a rapid onset and has a short duration, due to a traumatic episode. Term used to describe the first 24–48 hours after onset of an injury such as that sustained during a sporting activity.

acute respiratory distress syndrome (ARDS) characterized by difficulty breathing, poor oxygenation, stiff lungs and typical changes on a chest X-ray, following a recognized cause of acute lung injury. Analysis of arterial blood gases reveals a fall in PaO₂ and eventually an increased PaCO₂ and a fall in pH.

acute tubular necrosis (ATN) rapid onset necrosis of the renal tubules. It is usually caused by renal ischaemia due to shock, but may be due to the nephrotoxic effects of bacterial or chemical toxins. See also renal failure.

acute yellow atrophy acute diffuse necrosis of the liver; icterus gravis; malignant jaundice.

acyesis absence of pregnancy.

acystia congenital absence of the bladder.

adactyly absence of fingers.

Addison’s disease deficient secretion of cortisol and aldosterone due to primary failure of the adrenal cortex, causing electrolyte imbalance, diminished blood volume, hypotension, weight loss, hypoglycaemia, muscular weakness, gastrointestinal upsets and pigmentation of skin.

address a number which designates a particular storage area in the memory of the computer.

adduct to draw towards the midline of the body. See also abduct.

adduction the act of adducting, drawing towards the midline of the body. See also abduction.

adductor any muscle which moves a part toward the median axis of the body. See also abductor.

adenectomy surgical removal of a gland.

adenitis inflammation of a gland, or lymph node. hilar adenitis inflammation of bronchial lymph nodes.

adenoacanthoma a tumour of glandular tissue which may be benign or malignant and is identified by changes in the squamous cells.

adenocarcinoma a malignant epithelial cell tumour of glandular tissue.

adenofibroma see fibroadenoma.

adenoid resembling a gland. See also adenoids.

adenoidectomy surgical removal from the nasopharynx of enlarged pharyngeal tonsil (adenoid tissue).

adenoids abnormally enlarged pharyngeal tonsils. Lymphoid tissue situated in the nasopharynx which can obstruct breathing and impede hearing.

adenoma a benign, premalignant tumour of glandular epithelial tissue.

adenomatous polyp a benign tumour of the large intestine which may develop into a malignant tumour.

adenomyoma a non-malignant tumour composed of muscle and glandular elements, usually applied to benign growths of the uterus.

adenopathy any disease of a gland.

adenosine diphosphate (ADP) an important cellular metabolite involved in energy exchange within the cell. Chemical energy is conserved in the cell, by the phosphorylation of ADP to ATP primarily in the mitochondrion, as a high-energy phosphate bond.

adenosine monophosphate (AMP) an important cellular metabolite involved in energy release for cell use.

adenosine triphosphate (ATP) an intermediate high-energy compound which on hydrolysis to ADP releases chemically useful energy. ATP is generated during catabolism and utilized during anabolism.

adenotonsillectomy surgical removal of the pharyngeal tonsil (adenoid tissue) and palatine tonsils.

adenovirus a group of DNA-containing viruses. They cause upper respiratory and gastrointestinal infections and conjunctivitis.

adhesion abnormal union of two parts, occurring after inflammation; a band of fibrous tissue which joins such parts. In the abdomen such a band may cause intestinal obstruction; in joints it restricts movement; between two surfaces of pleura it prevents complete pneumothorax.

adipose fat; of a fatty nature. The cells constituting adipose tissue contain either white or brown fat.

adiposity excessive accumulation of fat in the body.

aditus in anatomy, an entrance or opening.

adjustable template a large number of parallel rods or pins which can be adjusted to the patient shape and clamped into position to show the patient contour.

adjuvant a treatment or drug used alongside another to increase its efficiency or effectiveness.

adjuvant therapy a treatment given together with another. It is usually applied to the treatment of cancer where cytotoxic drugs are used after removal of the tumour by surgery or radiotherapy. The purpose of treatment is to enhance the chance of cure and prevent recurrence. See also neoadjuvant therapy.

adnexa structures that are in close proximity to a part.

adnexa oculi the lacrimal apparatus.

adnexa uteri the ovaries and uterine (fallopian) tubes.

adrenal near the kidney. adrenal glands endocrine glands, one situated on the upper pole of each kidney. The adrenal cortex secretes glucocorticoids, mineralocorticoids and sex hormones which control metabolism, the chemical constitution of body fluids and secondary sexual characteristics. Under the control of the pituitary gland via the secretion of adrenocorticotrophic hormone. The adrenal medulla secretes noradrenaline (norepinephrine) and adrenaline (epinephrine). See also adrenalectomy.

adrenalectomy removal of an adrenal gland, usually for tumour. If both adrenal glands are removed, replacement administration of cortical hormones is required.

adrenaline (epinephrine) a catecholamine hormone, produced by the adrenal medulla. It enhances the effects of the sympathetic nervous system during times of physiological stress by preparing the body for ‘fight or flight’ responses. These include increased heart rate, bronchodilation and increased respiratory rate and glucose release. Adrenaline (epinephrine) is used therapeutically as a sympathomimetic in situations that include acute allergic reactions, and in local anaesthetic to prolong the anaesthetic effects.

adrenergic describes nerves which liberate the catecholamine noradrenaline (norepinephrine) from their terminations. Most sympathetic nerves release noradrenaline as a neurotransmitter.

adrenoceptor (adrenergic receptor) receptor sites on the effector structures innervated by sympathetic nerves. Two main types: alpha (α) and beta (β). Both receptor types, which respond differently to neurotransmitters, have further subdivisions.

adrenocorticotrophic hormone (ACTH, corticotrophin) secreted by the anterior lobe of the pituitary gland it stimulates the production of hormones by the adrenal cortex.

adrenogenital syndrome an endocrine disorder, usually congenital, resulting from abnormal activity of the adrenal cortex. A female child will show enlarged clitoris and possibly labial fusion, perhaps being confused with a male. The male child may show pubic hair and enlarged penis. In both male and female there is rapid growth, muscularity and advanced bone age.

adrenoleucodystrophy (ALD) a group of neurodegenerative disorders associated with adrenocortical insufficiency.

adult polycystic kidney diseases (APKD) see polycystic kidney disease.

advance directive a written declaration made by a mentally competent person setting out their wishes regarding life-prolonging medical interventions if they are incapacitated by an irreversible disease or are terminally ill, which prevents them making their wishes known to health professionals at the time. An advance directive is legally binding if it is in the form of an advanced refusal and the maker is competent at the time. Also known as a living will.

advanced life support (ALS) the use of drugs, artificial aids and advanced skills to save or preserve life during resuscitation procedures. See also cardiopulmonary resuscitation.

advancement surgical detachment of a tendon or muscle followed by re-attachment at an advanced point.

adventitia the external coat, especially of an artery or vein.

adverse drug reactions (ADRs) a term describing any unwanted effects of a drug. They range from very minor through to extremely unpleasant or life-threatening. They are classified into five types: A (augmented effects), B (bizarre effects), C (chronic effects), D (delayed effects) and E (ending effects, which occur when administration is stopped suddenly).

advocacy process by which a person supports or argues for the needs of another. Healthcare professionals may act as advocate for their patients or clients, or assist individuals to develop the skills needed for self-advocacy.

aerobe a microorganism that requires oxygen to maintain life.

aerobic requiring free oxygen or air to support life or a specific process. aerobic energy the production of adenosine triphosphate (ATP) by oxidative phosphorylation.

aerogenous gas producing.

aerophagia (aerophagy) excessive air swallowing.

aetiology (etiology) the study of the cause of disease.

afebrile without fever.

afferent conducting inward to a part or organ; used to describe nerves, blood and lymphatic vessels. See also efferent.

afferent degeneration that which spreads up sensory nerves.

afferent nerve one conveying impulses from the tissues to the nerve centres. Also known as sensory nerves.

affinity describes the chemical attraction between two substances, for example, oxygen and haemoglobin.

afibrinogenaemia a lack of fibrinogen resulting in a serious disorder of blood coagulation.

aflatoxin carcinogenic metabolites of certain strains of Aspergillus flavus that can affect peanuts and carbohydrate foods stored in warm humid climates. Hepatic enzymes produce the metabolites of aflatoxins which predispose to liver cancer.

aftercare the care given during convalescence and rehabilitation. It may be within the remit of health professionals such as therapists or nurses, or may be provided by social care staff or family members.

after-glow the production of light from a crystal after the irradiation of the crystal stops. See also phosphorescence.

afterload the pressure of blood in the pulmonary artery and aorta that forms the resistance that ventricular contraction must overcome to pump blood into the circulation. See also preload.

afterloading the method of inserting a number of guides into a body cavity and then mechanically inserting radioactive source over the guides. This technique reduces the radiation dose to the hands of the operator.

agammaglobulinaemia absence of gammaglobulin in the blood, with consequent inability to produce immunity to infection. See also Bruton’s agammaglobulinaemia.

aganglionosis absence of ganglia, as those of the distal bowel. See also Hirschsprung’s disease, megacolon.

agar a gelatinous substance obtained from certain seaweeds. It is used as a bulk-increasing laxative and for solidifying bacterial culture media.

ageism stereotyping people according to chronological age: overemphasizing negative aspects to the disadvantage of more positive points. Discriminatory attitudes in society disadvantage older people on the basis of age alone. However, ageist views can impact on people of any age.

agenesis incomplete and imperfect development.

age-specific death rate is the ratio of the number of deaths in a specific age group to the mean population of that age group multiplied by 100.

agglutinins antibodies that agglutinate or clump organisms or particles.

agility the ability to control the direction of the body or body part during rapid movement.

aglossia absence of the tongue.

aglutition difficulty in swallowing (dysphagia).

agnathia absence or incomplete development of the jaw.

agonist a muscle that shortens to perform a movement. Also describes a drug or other chemical that imitates the response of the natural chemical at a receptor site. See also antagonist.

agoraphobia morbid fear of being alone in large open places.

agranulocyte a non-granular leucocyte.

agranulocytosis marked reduction in or complete absence of granulocytes (polymorphonuclear leucocytes). Usually results from bone marrow depression caused by (a) hypersensitivity to drugs, (b) cytotoxic drugs or (c) irradiation. Symptoms include fever, ulceration of the mouth and throat. If untreated, prostration and death may ensue. See also neutropenia.

agraphia loss of language facility. See also motor agraphia, sensory agraphia.

AIDS-defining illness criteria for AIDS in a patient infected with HIV. Examples include candidiasis of bronchus, trachea, lungs or oesophagus, invasive cervical cancer, Kaposi’s sarcoma, pulmonary tuberculosis or other mycobacterial infection, and Pneumocystis carinii pneumonia.

air the gaseous mixture which makes up the atmosphere surrounding the earth. It consists of approximately 78% nitrogen, 20% oxygen, 0.04% carbon dioxide, 1% argon, and traces of ozone, neon, helium, etc. and a variable amount of water vapour.

air embolism results from an air bubble entering the circulation.

air hunger a deep indrawing of breath which characterizes the late stages of uncontrolled haemorrhage.

air knives are used in the drier section of automatic film processors to increase the velocity of the air as it strikes the film surface.

air swallowing (aerophagia) swallowing of excessive air particularly when eating: it may result in belching or the passage of flatus from the anus.

airway used to describe the entry to the larynx from the pharynx. See also Brook airway, oropharyngeal airway.

alactacid (alactic) anaerobic system a series of chemical reactions occurring within the cells whereby adenosine triphosphate for energy use is produced, without oxygen, from adenosine diphosphate (ADP) and creatine phosphate (phosphocreatine).

alactacid oxygen debt component the amount of oxygen required to replace the adenosine triphosphate (ATP) and creatine phosphate (phosphocreatine) stores in cells during the process of recovery from exercise.

ALARA a principle which states that the radiation dosage to patients and staff should be kept as low as reasonably achievable.

Albers–Schönberg disease see osteopetrosis.

albinism a congenital hypopigmentation of the hair, skin and eyes. It is caused by a deficiency of melanin pigment in skin and/or the eye. Other associated eye and neurological defects can contribute to poor vision.

albino a person affected with albinism.

albumin a protein found in animal and vegetable material. It is soluble in water and coagulates on heating. Serum albumin is the main protein of blood plasma.

albuminuria the presence of albumin in the urine. The condition may be temporary and clear up completely, may indicate serious kidney disease.

aldolase an enzyme present in muscle tissue.

aldolase test increased levels of aldolase and other enzymes in the blood are indicative of some muscle diseases, for example, severe muscular dystrophy.

aldosterone mineralocorticoid hormone secreted by the adrenal cortex. Secretion is regulated by the action of renin and angiotensin. It enhances the reabsorption of sodium accompanied by water and the excretion of potassium by the renal tubules.

aldosterone antagonist a drug that blocks the action of aldosterone.

Alexander technique a series of techniques used to improve the functioning of mind and body in movement known as ‘psychophysical’ re-education. It is based on the belief that poor posture can lead to ill health, injury and chronic pain. The technique aims to promote postural improvement through self-awareness.

alexia word blindness; an inability to interpret the significance of the printed or written word, but without loss of visual power. Can be due to a brain lesion or insufficient/inappropriate sensory experience during an ‘ab initio’ stage of learning.

alginates seaweed derivatives used in some wound dressings. They have high absorbency, haemostatic properties and can be removed without damaging delicate tissues.

algorithm logical steps which define how a problem can be solved. A step by step procedure for the solution of a problem by computer by using specific mathematical or logical operations. In CT the mathematical process used in image reconstruction, different algorithms may be used to produce differing images to better demonstrate particular structures.

aliasing in ultrasound when high velocities in one direction appear as high velocities in the opposite direction. It occurs when an analogue signal is sampled at a frequency which is lower than half its maximum frequency. All the frequency above half of the sampling frequency is projected below the base line (backfolded) in the low frequency region causing artefacts on the image. An artefact that occurs in magnetic resonance imaging due to the image encoding process, it occurs when the field of view is smaller than the area being imaged.

alimentary associated with food.

alimentary tract comprises the mouth, oesophagus, stomach, small intestine, ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anal canal.

alkali also called a base. Substances that have an excess of hydroxyl ions over hydrogen ions, for example, sodium bicarbonate. They have a pH greater than 7 and turn red litmus blue. Alkalis react with acids to produce salts plus water, and with fats to form soaps. alkaline reserve a biochemical term denoting the amount of buffered alkali (normally bicarbonate) available in the blood for buffering acids (normally dissolved CO₂) formed in or introduced into the body and limiting pH changes in the blood.

alkaline relating to or possessing the properties of an alkali. Containing an excess of hydroxyl over hydrogen ions.

alkaline phosphatase an enzyme present in several tissues, for example, bone, liver and kidney. An increase of this enzyme in the blood is indicative of obstructive jaundice and increased osteoblast activity associated with some bone disease.

alkalinuria alkalinity of urine.

alkaloid similar to an alkali. Also describes a large group of organic bases present in plants and which have important physiological actions, for example, morphine, atropine, quinine and caffeine.

allergen an antigen which produces an allergic, or immediate-type hypersensitivity response.

allergy hypersensitivity to a foreign substance that is normally harmless but causes a violent action in the patient, for example, asthma, hay fever, migraine, iodine-based contrast agents. See also anaphylaxis, sensitization.

allogenic transplant a transplant, usually of bone marrow, from an immunologically compatible sibling.

allograft grafting or transplanting an organ or tissue from one person to another who does not share the same transplantation antigens. Also known as a homograft.

alloy blocks shielding blocks of an alloy of lead, bismuth or cadmium placed on a tray on the radiotherapy accessory mount to shape the radiation beam so that it accurately covers the treatment area. Blocks can be individually made for each patient, accounting for beam divergence and pre-mounted on a tray.

alopecia partial or complete loss of hair which can be premature, congenital or senile.

alpha (α)-antitrypsin a liver protein that normally opposes trypsin. Reduced blood levels are linked with a genetic predisposition to emphysema and liver disease.

alpha decay the spontaneous emission of an alpha particle from the nucleus of an atom, resulting in the atomic number of the element decreasing by 2 and the mass number decreasing by 4.

alphafetoprotein (AFP) a protein produced by fetal gut and liver cells and by adult liver cancer cells. Raised levels are seen in maternal serum and amniotic fluid in fetal abnormalities including neural tube defects. May be used as a tumour marker for cancers of the liver and the testes affecting adults.

alpha particle the nucleus of a helium-4 atom consisting of two protons and two neutrons.

alternating current when electrons flow through a circuit in one direction and then the other.

altitudinal when describing a visual field defect implies loss of vision in superior or inferior half of field.

aluminium chloride used as a hardener in fixing solutions which contain acetic acid as the acid.

aluminium sulphate used as a hardener in fixing solutions which contain sulphuric acid as the acid.

alveolar ridge the part of the mandible and maxilla in which the teeth are embedded.

alveolitis inflammation of alveoli. When caused by inhalation of an allergen it is termed extrinsic allergic alveolitis.

alveolus an air sac of the lung. In dentistry, a bony tooth socket within the jaw bone. A gland follicle or acinus.

Alzheimer’s disease a progressive form of neuronal degeneration in the brain, a common case of dementia in older people which is irreversible. Can affect younger patients (i.e. under 65 years of age), often when there is a family history of the disease.

A-mode used in early ultrasound machines, the voltage was produced across the transducer as a vertical deflection on the face of the oscilloscope. The horizontal sweep was calibrated to indicate the distance from the transducer to the reflecting surface. Demonstrates only the position and length of a reflecting structure.

amalgam any of a group of alloys containing mercury. See also dental amalgam.

amastia congenital absence of the breasts.

amaurosis partial or total blindness.

amaurosis fugax temporary loss of vision in an eye due to interruption of arterial supply.

ambient light the light in the room where a film is being viewed.

ambulant able to walk.

ambulatory mobile, walking about.

ambulatory ECG (Holter monitoring) recording heart rhythm and rate over a 24-hour period to detect transient ischaemia or arrhythmias. The person continues with their normal activities and keeps a record of times and activities. See also electrocardiogram.

ambulatory surgery (day surgery) surgery carried out on the day of admission and, in the absence of problems, the person is discharged the same day to the care of the primary care team.

ambulatory treatment interventions such as blood product transfusion or chemotherapy, provided for patients on a day care basis. See also continuous ambulatory peritoneal dialysis.

amelia congenital absence of a limb or limbs. complete amelia absence of both arms and legs.

amelioration a reduction in the severity of symptoms.

amenorrhoea absence of menstruation. When menstruation has not been established at the time when it should have been, it is termed primary amenorrhoea; absence of menstruation after they have commenced is referred to as secondary amenorrhoea.

ametria congenital absence of the uterus.

amino acids organic acids in which one or more of the hydrogen atoms are replaced by the amino group, NH₂. They are the end product of protein hydrolysis and from them the body synthesizes its own proteins. They are classified as either essential (indispensable) or non-essential (dispensable). Ten (eight in adults and a further two during childhood) cannot be synthesized in sufficient quantities in the body and are therefore essential (indispensable) in the diet – arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. The remainder, which can be synthesized in the body if the diet contains sufficient amounts of the precursor amino acids, are designated non-essential (dispensable) amino acids. However, some of these are conditionally essential and depend upon adequate amounts of their precursor.

aminoaciduria the abnormal presence of amino acids in the urine; it usually indicates an inborn error of metabolism as in cystinosis and Fanconi syndrome.

aminopeptidases intestinal enzymes that act upon the amine end of the peptide chain during the digestion of protein.

ammonia a compound of nitrogen and hydrogen. Several inherited errors of ammonia metabolism can cause learning disability, seizures and other neurological manifestations.

ammonium thiosulphate used as a fixing agent in fixer solutions.

amnesia complete loss of memory; can be divided into organic (true) amnesia (for example, delirium, dementia), and psychogenic amnesia (for example dissociative states). The term anterograde amnesia is used when there is poor recall of events following an accident or brain injury, and retrograde amnesia when the loss of memory is prior to the injury.

amnesic syndrome chronic profound impairment of recent memory with preserved immediate recall. Often accompanied by disorientation for time and confabulation (the creation of false memory to fill the gaps in memory). Commonly caused by thiamin(e) deficiency, which can be secondary to chronic alcohol use, dietary deficiency, gastric cancer, etc.

amniocentesis a diagnostic procedure for detecting chromosomal, metabolic and haematological abnormalities of the fetus. It involves inserting a needle under ultrasound guidance through the abdominal wall into the amniotic sac to obtain a sample of amniotic fluid.

amnion membrane of embryonic origin lining the cavity of the uterus during pregnancy containing amniotic fluid and the fetus.

amnionitis inflammation of the inner fetal membrane (the amnion).

amnioscopy an instrument that when passed through the abdominal wall enables viewing of the fetus and amniotic fluid. Clear, colourless fluid is normal; yellow or green staining is due to meconium and occurs in cases of fetal hypoxia. cervical amnioscopy can be performed late in pregnancy. A different instrument is inserted via the vagina and cervix for the same reasons.

amniotic cavity the fluid-filled cavity between the fetus and the inner fetal membrane (amnion).

amniotic fluid fluid produced by the inner fetal membrane (amnion) and the fetus, which surrounds the fetus throughout pregnancy. It protects the fetus from temperature variations and physical trauma, and permits fetal movement. It is secreted and reabsorbed by cells lining the amniotic cavity and is swallowed by the fetus and excreted as urine. See also amniocentesis, amnioscopy.

amniotic fluid embolism an embolus caused by amniotic fluid entering the maternal circulation. An extremely rare but very serious complication of pregnancy.

amoeba a unicellular (single cell) protozoon. Strains that are human parasites include Entamoeba histolytica, which causes amoebic dysentery (intestinal amoebiasis).

amoebiasis infestation of large intestine by the protozoon Entamoeba histolytica, where it causes mucosal ulceration leading to pain, diarrhoea alternating with constipation and blood and mucus passed rectally, hence the term ‘amoebic dysentery’. If the amoebae enter the hepatic portal circulation they may cause a liver abscess. Diagnosis is by isolating the amoeba in the stools. Cutaneous amoebiasis may cause perianal or genital ulceration in homosexual men.

amoeboid resembling an amoeba in shape or in mode of movement such as leucocytes.

amoeboma a tumour in the caecum or rectum caused by Entamoeba histolytica. Fibrosis may occur and obstruct the bowel.

amorph a gene that is inactive, i.e. does not express a trait.

amorphous not having a regular shape.

ampere (A) one of the seven base units of the International System of Units (SI). A measurement of electrical current.

amphiarthroses cartilagenous joints which either have no movement or minimal movement, for example the joint between the epiphysis and diaphysis of a growing long bone, symphysis pubis.

amplification gain is the measure of the extent to which developer increases the initial effect of exposure on the silver halide grains.

amplitude the maximum value of either positive or negative current or voltage that occurs on an alternating current waveform. In ultrasound, the magnitude (height) of the ultrasound beam, the ultrasound pulse is very brief so the power values arranged over a period of time will be low compared to peak intensity. See also peak value.

ampoule a sealed glass or plastic phial containing a single sterile dose of a drug.

ampulla any flask-like dilatation such as that in the uterine (fallopian) tube.

ampulla of Vater the enlargement formed by the union of the common bile duct with the pancreatic duct where they enter the duodenum.

amputation removal of an appending part, for example, limb.

amputee a person who has had amputation of one or more limbs.

amylase any enzyme that converts starches into sugars. Found in saliva and pancreatic juice; it converts starchy foods to maltose. The amount of amylase in the blood is increased in disorders of the pancreas such as pancreatitis.

amyloidosis formation and deposit of amyloid in any organ, notably the liver and kidney. primary amyloidosis has no apparent cause. secondary amyloidosis can occur in any prolonged toxic condition such as Hodgkin’s disease, tuberculosis and leprosy. It is common in the genetic disease familial Mediterranean fever.

amyotrophic lateral sclerosis (ALS) a form of motor neuron disease in which there is a loss of the upper motor neurons from the cortex to the brainstem and spinal cord as well as the loss of the lower motor neurons from the brainstem and spinal cord to the muscles.

anacrotic a wave in the ascending curve of an arterial tracing, indicating the opening of the aortic valve (that between the left ventricle and the aorta). An abnormality of this occurs in aortic stenosis. See also dicrotic.

anaemia a deficiency in either the quantity or quality of red corpuscles in the blood. Produces clinical manifestations arising from hypoxaemia, such as lassitude and breathlessness on exertion. There are very many possible causes, for example, haemolytic disease of the newborn, megaloblastic anaemia, thalassaemia. See also aplastic anaemia, haemolytic anaemia, pernicious anaemia.

anaemia of chronic disease anaemia associated with chronic inflammatory diseases, infection or cancer.

anaerobe a microorganism that is unable to grow in the presence of molecular oxygen for example gangrene.

anaerobic relating to the absence of oxygen. Describes processes that occur without oxygen, and certain microorganisms that survive without free oxygen or air. anaerobic energy energy that is produced without using oxygen via two energy systems: alactacid and lactacid.

anaesthesia loss of sensation. general anaesthesia loss of sensation with loss of consciousness. In local anaesthesia injection of a drug that inhibits peripheral nerve conduction so that painful stimuli fail to reach the brain. Spinal anaesthesia loss of sensation by the injection of local anaesthetic into the cerebrospinal fluid between the vertebrae usually of the lower back, causing loss of sensation but no loss of consciousness. Also used to describe the loss of feeling produced by a spinal lesion. See also caudal anaesthesia, epidural anaesthesia.

anaesthesiology the science dealing with anaesthetics, their administration and effect.

anaesthetic a drug that induces general or local loss of sensation. general anaesthetic a drug that produces unconsciousness by inhalation or injection. local anaesthetic a drug that injected into the tissues or applied topically causes local insensibility to pain. See also spinal anaesthetic.

anaesthetist a doctor with specialist training to administer general anaesthesia.

anaesthetize to administer drugs or gases to produce general anaesthesia.

analeptic restorative.

analgesia the relief of pain without causing unconsciousness. Loss of sensation of pain without loss of touch.

analgesic a drug used to relieve pain without causing unconsciousness.

analogue represents a quantity changing in steps which are continuous, as opposed to digital which is in discrete steps.

analogue signal a continuous electrical signal used to transmit images to a computer, television.

analogue to digital converter a device which converts analogue signals into digital signals which can be understood and manipulated by a computer.

analysis of variance (ANOVA) a statistical method of comparing sample means.

analytical epidemiology the study of the relationship between different risk factors and the development of disease.

anaphylactic shock shock caused by an allergic reaction.

anaphylaxis a severe reaction, often fatal occurring in response to drugs, bee stings and food allergies. The symptoms are, severe difficulty in breathing, rapid pulse, sweating and collapse. See also allergy, sensitization.

anaplasia loss of the distinctive characteristics of a cell, associated with proliferative activity as in cancer.

anaplastic carcinoma a malignant tumour of the thyroid gland which grows rapidly and is more common in the elderly. It is relatively resistant to radiotherapy.

anarthria a severe form of dysarthria. The affected person is unable to produce the motor movements required for speech. The muscle weakness is apparent in the phonatory, articulatory, respiratory and resonatory speech systems. See also dysarthria.

anastomosis the anatomical intercommunication of the branches of two or more tubular structures, for example, arteries or veins. In surgery, the establishment of an intercommunication between two hollow organs, vessels or nerves.

anatomical position for the purpose of accurate description the anterior view is of the upright body facing forward, hands by the sides with palms facing forwards. The posterior view is of the back of the upright body in that position (see figure on p. 21).

ancylostomiasis (hookworm disease, miners’ anaemia) infestation of the human intestine with Ancylostoma, giving rise to malnutrition and severe anaemia.

androblastoma (arrhenoblastoma) a tumour of the ovary; can produce male or female hormones and can cause masculinization in women or precocious puberty in girls.

androgens steroid hormones secreted by the testes (testosterone) and adrenal cortex in both sexes. They have widespread anabolic effects, produce the male secondary sex characteristics, for example, male hair distribution and stimulate spermatogenesis.

anechoic without echoes.

anencephaly

absence of the cranial skull, which begins to ossify at 10 weeks interuterine life, and the brain. The condition is incompatible with life. It can be detected by raised levels of alphafetoprotein in the amniotic fluid.

aneuploidy any variation in the number of chromosomes, refers to individual chromosomes rather than sets of chromosomes, for example, more chromosomes are present in Down syndrome.

aneurysm local dilatation of a blood vessel, usually an artery, due to a local fault in the wall through defect, disease or injury, producing a swelling, often pulsating, over which a murmur may be heard. The pressure of blood can cause the swelling to increase in size and rupture. See also dissecting aneurysm, fusiform aneurysm, saccular aneurysm.

Angelman syndrome an inherited condition that arises from mutations in the maternal chromosome 15 during formation of the gamete. Features include: ‘puppet-like’ gait, learning disability, brachycephaly (short, broad skull), inappropriate emotional outbursts, tongue protrusion and hooked nose.

angiectasis abnormal dilatation of blood vessels. See also telangiectasis.

angiitis inflammation of a blood or lymph vessel. See also vasculitis.

angina sense of constriction.

angina pectoris severe but temporary attack of cardiac pain that may radiate to the arms, throat, lower jaw or the back. Results from myocardial ischaemia. Often the attack is induced by exercise (angina of effort).

angiocardiography the radiographic demonstration of the heart and great vessels by injecting a contrast agent via a catheter in the brachial or femoral arteries.

angiodysplasia vascular malformation initially involving the large bowel, which may cause lower gastrointestinal bleeding.

angiogenesis the formation of new blood vessels (vascularization), for example, during wound healing, or the development of new blood vessels supplying a tumour.

angiography demonstration of the blood vessels of the arterial system after injection of a contrast agent into an artery.

angiology the science dealing with blood and lymphatic vessels.

angioma any bengin tumour with blood or lymph vessels.

angio-oedema (angioneurotic oedema) a severe form of urticaria which may involve the skin of the face, hands or genitalia and the mucous membrane of the mouth and throat; oedema of the glottis may be fatal. Immediately there is an abrupt local increase in vascular permeability, as a result of which fluid escapes from blood vessels into surrounding tissues. Swelling may be due to an allergic hypersensitivity reaction to drugs, pollens or other known allergens, but in many cases no cause can be found.

angioplasty surgery on a narrow artery to increase the blood flow through the vessel. See also percutaneous transluminal angioplasty, transluminal angioplasty.

angiosarcoma a malignant tumour arising from blood vessels.

angiospasm spasm of blood vessels.

angiotensin a substance formed by the action of renin on a precursor protein in the blood plasma. In the lungs angiotensin I is converted into angiotensin II, a highly active substance which constricts blood vessels and causes release of aldosterone from the adrenal cortex in the angiotensin– aldosterone response.

angle of insonation this is important in pulsed Doppler ultrasound examinations to obtain an accurate representation of blood flow and should be 60ö or less.

angular frequency in magnetic resonance is the frequency of oscillation or rotation.

anhydraemia deficient fluid content of blood.

anhydrous entirely without water, dry.

anicteric without jaundice.

anion a negatively charged ion, for example chloride (Cl⁻). They move towards the positive electrode (anode) during electrolysis.

anion gap the difference between the amount of anions and cations in the blood. See also cation.

aniridia congenital absence of the iris.

anisomelia unequal length of limbs.

ankle the synovial saddle joint formed between the talus, fibula and tibia.

ankle equinus a congenital or acquired condition or deformity, which is characterized by deficient dorsiflexion at the ankle joint. During the stance phase of normal gait a minimum 10ö of ankle joint dorsiflexion is needed for normal walking. See also talipes.

alkylating agent organic molecules that disrupt cell division by binding to the DNA in the nucleus. See also cytotoxic.

ankyloblepharon adhesion of the eyelid margins, usually lateral, often secondary to chronic inflammation.

ankylosing spondylitis an inflammatory condition affecting the spine and sacroiliac joints and characterized (in its later stages) by ossification of the spinal ligaments and ankylosis of sacroiliac joints. It occurs most commonly in young men. See also spondylitis.

ankylosis stiffness or fixation of a joint. See also spondylitis.

annular ring-shaped. annular ligaments hold in proximity two long bones, as in the wrist and ankle joints.

annular array in ultrasound, using crystals of the same frequency which are arranged in a circle and are electronically focussed at several depths.

anode part of an X-ray tube that is made of either copper with a tungsten target embedded in it, or molybdenum with a tungsten/rhenium target; the positive anode can be either stationary or rotating. The target is at an angle to produce a larger effective focal spot.

anode heel effect due to the angle of the target on the anode of an X-ray tube, some of the radiation produced is absorbed by the target and therefore the intensity of the emergent X-ray beam is greater at the cathode end of the tube than at the anode end.

anogenital associated with the anus and the genital region.

anomaly that which is unusual or differs from the normal.

anomaly scan an ultrasound scan undertaken in the second trimester, usually between 20 and 22 weeks, to look for any fetal abnormalities and the position of the placenta.

anoplasty surgical repair or reconstruction of the anus.

anorchism congenital absence of one or both testes.

anorectal associated with the anus and rectum, for example, a fissure.

anorexia lack of appetite for food. anorexia nervosa a psychological illness, most common in female adolescents. There is avoidance of carbohydrate intake leading to weight loss. There is associated over-exercising, purging and disturbance of body image. Can lead to mortality by starvation in severe cases. See also eating disorders.

anosmia absence of the sense of smell.

anovular relating to absence of ovulation.

anovular bleeding occurs in dysfunctional uterine bleeding associated with hormone disturbance.

anovular menstruation is bleeding as the result of taking oral contraceptives.

anoxaemia literally, no oxygen in the blood. Usually used to indicate hypoxaemia.

anoxia literally, no oxygen in the tissues. Usually used to signify hypoxia.

antagonist a muscle that reverses or opposes the action of an agonist muscle. Also describes a drug or chemical that blocks the action of another molecule at a cell receptor site, for example, the narcotic antagonist naloxone reverses the action of opioid drugs. See also agonist.

antagonistic action action performed by those muscles that limit the movement of an opposing group.

antegrade pyelography the radiographic examination of the renal tract following the infusion of contrast agent directly into the renal pelvis.

anteflexion the bending forward of an organ, commonly applied to the position of the uterus. See also retroflexion.

antemortem before death. See also postmortem.

antenatal before birth (prenatal). See also postnatal.

antepartum before birth. From 24 weeks’ gestation to full term. See also postpartum.

anterior in front of; the front surface of; ventral. See also posterior.

anterior chamber of the eye the space between the poster-ior surface of the cornea and the anterior surface of the iris. See also aqueous.

anterior tibial syndrome severe pain and inflammation over anterior tibial muscle group, with inability to dorsiflex the foot.

anterograde proceeding forward. See also retrograde.

anteroposterior radiograph a radiograph taken from the front to the back of the body (see Figure on p. 25).

anteversion the normal forward tilting, or displacement forward, of an organ or part. See also retroversion.

anthracosis accumulation of carbon in the lungs due to inhalation of coal dust; may cause fibrotic reaction. A form of pneumoconiosis.

anthrax

a contagious disease of domestic animals such as cattle, which may be transmitted to humans by inoculation, inhalation and ingestion, causing malignant pustule (skin lesion) with septicaemia, inhalation anthrax or woolsorter’s disease (haemorrhagic bronchopneumonia), meningitis and severe gastroenteritis. Causative organism is the bacterium Bacillus anthracis. Preventive measures include immunization of humans and animals, post-exposure prophylaxis with antibiotics, for example, ciprofloxacin, and proper disposal of infected animals. Occupations at high risk include veterinary surgeons, livestock farmers, butchers, and those handling hides and wool.

anthropoid resembling man. The word is also used to describe a pelvis that is narrow from side to side, a form of contracted pelvis.

anthropological baseline a line joining the infraorbital margin to the superior border of the external auditory meatus (see Figure below).

anthropology the study of humankind. Subdivided into several specialties. See also ethnography.

anthropometry measurement of the human body and its parts for the purposes of comparison and establishing norms for sex, age, weight, race and so on.

anti-anabolic preventing the synthesis of body protein.

antibacterial describes an agent that destroys bacteria or inhibits their growth. See also antibiotics, antiseptics, bactericidal, bacteriostatic, disinfectants.

antibiotic the term generally used for all drugs that act against bacteria. Some have a narrow spectrum of activity whereas others act against a wide range of bacteria (broad spectrum).

antibodies a substance, either natural or introduced, that helps to protect the body against infection.

anticoagulant an agent that reduces the propensity of blood to clot. Uses: (a) to obtain specimens suitable for pathological examination and chemical analyses where whole blood or plasma is required instead of serum; (b) during the collection of blood for transfusion, the anticoagulant usually being sodium citrate; (c) as therapy in the prophylaxis and treatment of thromboembolic conditions, for example, heparin.

anticoagulation the process of suppressing or reducing blood coagulation.

anti-curl backing used for single emulsion films and coat the opposite side of the base from the emulsion to prevent the film from curling.

anti-D an antibody directed against the Rhesus D blood group antigen. Given to RhD-negative women who have RhD-positive babies to prevent subsequent immune-mediated disease such as haemolytic disease of the newborn.

antidiuretic reducing the volume of urine.

antidiuretic hormone (ADH) vasopressin.

antiemetic any agent such as a drug that prevents or treats nausea and vomiting.

antienzyme a substance that exerts a specific inhibiting action on an enzyme. Found in the digestive tract to prevent autodigestion of the mucosa, and in blood where they act as immunoglobulins.

anti-frothant a chemical added to the developer to reduce foaming due to agitation of the developer by the rollers.

anti-GBM disease disease caused by specific antibodies to the glomerular basement membranes. It features rapidly progressive glomerulonephritis and pulmonary haemorrhage. Previously known as Goodpasture’s disease.

antigen substance that stimulates the production of a specific immune response.

antihaemophilic factor (AHF) factor VIII in the blood coagulation cascade, present in plasma. A deficiency causes haemophilia A (classical).

anti-halation layer a coloured dye in the anti-curl backing of a film to absorb any reflected light and therefore prevent unsharpness on the film.

antihistamine a drug which suppresses some of the effects of histamine released in the body as a result of an allergic reaction.

antihypertensive describes any agent that reduces high blood pressure.

anti-infective describes any agent which prevents infection.

anti-inflammatory tending to prevent or relieve inflammation.

antilymphocyte globulin (ALG) an immunoglobulin which binds to antigens on T cells and inhibits T cell-dependent immune responses; occasionally used in preventing graft rejection during organ transplantation.

antimetabolites one of a group of chemical compounds which prevent the effective use of the corresponding metabolite, and interfere with normal growth or cell mitosis if the process requires that metabolite.

antimitochondrial antibody (AMA) autoantibodies against mitochondrial components. Certain types are a marker for primary biliary cirrhosis.

antineoplastic describes any substance or procedure that kills or slows the growth of cancerous/neoplastic cells, such as cytotoxic chemotherapy, radiotherapy, or hormonal or biological response modification therapy.

anti-neutrophil cytoplasmic antibody (ANCA) a group of autoantibodies directed against cytoplasmic components of neutrophils and associated with a range of pathological conditions such as polyarteritis.

antinuclear antibody (ANA) a family of many types of autoantibody directed against cell nuclei that are found in connective tissue disorders, particularly systemic lupus erythematosus (SLE) and Sjögren syndrome. The many types recognized can be used to categorize rheumatological disorders.

antioxidants substances that delay the process of oxidation. Some minerals, for example, zinc, and vitamins A, C and E, contained in a balanced diet, function as antioxidants and help to minimize free radical oxidative damage to cells.

antiperistalsis reversal of the normal peristaltic action.

antiprothrombin (anticoagulant) stops blood coagulation by preventing conversion of prothrombin into thrombin.

antisepsis prevention of sepsis (tissue infection); introduced into surgical procedures in 1880 by Lord Lister.

antiseptics chemical substances that destroy or inhibit the growth of microorganisms. They can be applied to living tissues, for example, chlorhexidine used for skin preparation before invasive procedures and hand decontamination.

antiserum serum prepared from the blood of an animal immunized by the requisite antigen, containing a high concentration of polyclonal antibodies against that antigen.

antispasmodic (spasmolytic) describes any measure or drugs used to relieve spasm in muscle.

antistatic preventing the accumulation of static electricity.

antistreptolysin against streptolysins. A raised antistreptolysin titre in the blood is indicative of recent streptococcal infection.

antithrombin III substance that inhibits blood coagulation. It is synthesized in the liver and is normally present in the blood, where it restricts coagulation to areas where it is needed. See also thrombin.

antithyroid any agent used to decrease the activity of the thyroid gland.

antitoxin an antibody which neutralizes a given toxin. Made in response to the invasion by toxin-producing bacteria, or the injection of toxoids.

antituberculosis drugs drugs used in the treatment of tuberculosis.

antitumour antibiotics cytotoxic antibiotics that act against tumour cells by disrupting cell membranes and DNA. See also cytotoxic.

antitussive describes any measures which suppress a cough.

antiviral acting against viruses.

antrectomy surgical excision of the antrum of the stomach.

antro-oral associated with the maxillary antrum and the mouth.

antrostomy surgical opening from nasal cavity to antrum of Highmore (maxillary sinus).

antrum a cavity, especially in bone.

anuria complete absence of urine output by the kidneys.

anus the end of the alimentary canal, at the extreme termination of the rectum. It is formed of a sphincter muscle which relaxes to allow faecal matter to pass through. See also artificial anus, imperforate anus.

aorta the main artery arising out of the left ventricle of the heart.

aortic associated with the aorta.

aortic incompetence regurgitation of blood from the aorta back into the left ventricle.

aortic murmur abnormal heart sound heard over aortic area; a systolic murmur alone is the murmur of aortic stenosis, a diastolic murmur denotes aortic regurgitation.

aortic regurgitation (incompetence) regurgitation of blood from aorta back into the left ventricle.

aortic stenosis narrowing of aortic valve. This is usually due to rheumatic heart disease or a congenital bicuspid valve which predisposes to the deposit of calcium.

aortitis inflammation of the aorta.

aortography demonstration of the aorta after introduction of a radiographic contrast agent, either via a catheter passed along the femoral or brachial artery or by direct translumbar injection.

aperient a mild drug given to produce peristaltic action in the bowel and therefore emptying. See also laxative.

aperistalsis absence of peristaltic movement in the bowel. Characterizes the condition of paralytic ileus.

Apert’s syndrome congenital craniosynostosis accompanied by deformities of the hands. See also acrocephalosyndactyly, syndactyly.

apex the summit or top of anything which is cone-shaped, for example, the tip of a lung. In a heart of normal size the apex beat (systolic impulse) can be seen or felt in the 5th left intercostal space in the mid-clavicular line. It is the lowest and most lateral point at which an impulse can be detected and provides a rough indication of the size of the heart.

Apgar score a measure used to evaluate the general condition of a newborn baby, developed by an American anaesthetist, Dr Virginia Apgar. A score of 0, 1 or 2 is given for the criteria of heart rate, respiratory effort, skin colour, muscle tone and response to stimulation. A score between 8 and 10 indicates a baby in good condition.

aphagia inability to swallow.

aphakia absence of the lens. Describes the eye after removal of a cataract without artificial lens implantation.

aphasia a language disorder that follows brain damage, due primarily to an impaired linguistic system. The term does not describe language disorders that involve problems with expression or comprehension caused by mental health problems, including psychoses, confusion and dementia, or muscle weakness, or problems with hearing. There are several classifications but generally aphasia is described as being expressive (motor) aphasia or receptive (sensory) aphasia. However, many people exhibit problems with both language expression and comprehension. See also dysarthria.

aphonia inability to make sound due to neurological, behavioural, psychogenic or organic causes. See also dysarthria.

aphthae small ulcers of the gastrointestinal mucosa surrounded by a ring of erythema.

apical the summit or apex.

apical projection a radiographic examination of the lung apices, using an angled beam to project the clavicles away from the lung tissue.

apical foramen a hole at the base of the root of a tooth which allows the passage of blood vessels and nerves.

apicectomy excision of the apex of the root of a tooth.

aplasia incomplete development of tissue or an organ; absence of growth.

aplastic without structure or form. Incapable of forming new tissue. aplastic anaemia is the result of complete bone marrow failure.

apnoea absence of breathing for short periods as seen in Cheyne–Stokes respiration. It is due to lack of the necessary CO₂ tension in the blood for stimulation of the respiratory centre. See also periodic breathing.

apocrine glands modified sweat glands, especially in axillae, genital and perineal regions. Responsible after puberty for body odour. See also eccrine.

apodia congenital absence of the feet.

aponeurosis a broad glistening sheet of tendon-like tissue which serves to invest and attach muscles, for example, abdominal muscles, to each other, and also to the parts that they move.

aponeurositis inflammation of an aponeurosis.

apophysis a projection, protuberance or outgrowth. Usually used in connection with bone.

apoplexy obsolete term for cerebrovascular accident (stroke).

apoptosis programmed cell death.

apparent focal spot the target of an X-ray tube is at an angle to allow a larger area to be struck by electrons while still maintaining the smaller, apparent, focal spot when viewing from the tube port.

appendectomy see appendicectomy.

appendicectomy excision of the veriform appendix.

appendicitis inflammation of the veriform appendix.

appendicular skeleton the bones forming the pectoral girdle, upper limbs, pelvic girdle and lower limbs.

appendix an appendage. veriform appendix a worm-like appendage of the caecum about the thickness of a pencil and usually measuring from 2.5 to 15 cm in length. It contains lymphoid tissue and its position is variable.

appetite the desire for food, influenced by physical activity, metabolic, dietary, psychological and behavioural factors. It may be increased or decreased pharmacologically. Appetite is also influenced by health status. See also anorexia, bulimia, eating disorders.

applicator an instrument used for local application of remedies, for example, vaginal medication applicator. In radiotherapy attached to the tube housing to provide an accurate means of setting up the source–skin distance and is a form of secondary collimation. See also Fulfield applicator.

apposition the approximation or bringing together of two surfaces or edges.

appraisal making a valuation. performance appraisal or review a formal procedure whereby an appraiser (manager) systematically reviews the role performance of the appraisee and they jointly set goals for the future.

approved name the generic or non-proprietary name of a drug, such as salbutamol. Should be used in prescribing except in the case of drugs where bioavailability differs between brands.

apraxia inability to perform a motor act or use an object normally, due typically to damage in the parietal lobe of the brain.

apyrexia absence of fever.

aqueduct a canal. aqueduct of Sylvius the canal connecting the 3rd and 4th ventricles of the brain; aqueductus cerebri.

aqueous watery.

aqueous humour the fluid contained in the anterior and posterior chambers of the eye.

arachnodactyly congenital abnormality resulting in long, slender fingers. Said to resemble spider legs (hence ‘spider fingers’).

arachnoid resembling a spider’s web.

arachnoid mater (membrane) a delicate membrane enveloping the brain and spinal cord, lying between the pia mater internally and the dura mater externally; the middle membrane of the meninges.

arborization an arrangement resembling the branching of a tree. Characterizes both ends of a neuron, i.e. the dendrites and the axon as it supplies each muscle fibre.

arboviruses abbreviation for ARthropod-BOrne viruses. Include various RNA viruses transmitted by arthropods: mosquitoes, ticks, sandflies, etc. They cause diseases such as yellow fever, dengue, sandfly fever and several types of encephalitis.

arch aortography the radiographic examination of the aorta and its major branches by injecting a contrast agent via femoral or axillary catheterization.

arch of aorta the proximal one of the four portions of the aorta giving rise to the three arterial branches called the innominate (brachiocephalic) left common carotid and left subclavian arteries.

archival permanence the length of time a radiographic film can be stored without significant deterioration of image quality.

arc therapy when a source of radiation moves through a prescribed angle during treatment.

arcus senilis an opaque ring round the edge of the cornea, seen in old people.

areola the pigmented area round the nipple of the breast. A secondary areola surrounds the primary areola in pregnancy.

areolar tissue a loose connective tissue consisting of cells and fibres in a semisolid matrix.

arginase an enzyme present in the liver, kidney and spleen. It converts arginine into ornithine and urea.

ariboflavinosis a deficiency state caused by lack of riboflavin and other members of the vitamin B complex. Characterized by cheilosis, seborrhoea, angular stomatitis, glossitis and photophobia.

Arnold–Chiari malformation a group of disorders affecting the base of the brain. Commonly occurs in hydrocephalus associated with meningocele and myelomeningocele. There are degrees of severity but usually there is some ‘kinking’ or ‘buckling’ of the brainstem with cerebellar tissue herniating through the foramen magnum at the base of the skull.

array an arrangement of components. See also annular array, linear array, curved array, phased array.

arrectores pilorum internal, plain, involuntary muscles attached to hair follicles, which, by contraction, erect the hair follicles, causing ‘gooseflesh’.

arrhythmia any deviation from the normal rhythm, usually referring to the heart beat. See also asystole, extrasystole, fibrillation, heart, tachycardia.

artefact in magnetic resonance where an additional image occurs in the reconstructed image which does not match the anatomy or pathology in the patient. In ultrasound an abnormality on an image which is due to data acquisition, processing or the nature of the ultrasound beam.

arterial blood gases (ABGs) measurement of the oxygen (PaO₂), carbon dioxide (PaCO₂) and acid–base (pH or hydrogen ion concentration) content of the arterial blood.

arterial haemorrhage the loss of blood from an artery.

arterial line cannula placed in an artery to sample blood for gas analysis and for continuous blood pressure monitoring. Usually used only in specialist units (ITU, HDU and theatre) because of the potential risk of severe blood loss. They should always be attached to a pressure transducer and monitor, and have an alarm that indicates any disconnection. See also arterial blood gases, blood pressure.

arterial ulcer a leg ulcer caused by a defect in arterial blood supply. They are found on the foot, usually between the toes or close to the ankle; the adjacent skin is discoloured, shiny and hairless; and the ulcer is small and deep with some exudate. They are often associated with a history of cardiovascular disease or diabetes mellitus.

arteriography demonstration of the arterial system after injection of a radiographic contrast agent.

arteriole a small artery, joining an artery to a capillary network. They control the amount of blood entering the capillary network. They are able to constrict and dilate to change peripheral resistance thereby influencing blood pressure.

arteriopathy disease of any artery.

arterioplasty reconstructive surgery applied to an artery.

arteriosclerosis degenerative arterial change associated with advancing age. Primarily a thickening of the media (middle) layer and usually associated with some degree of atheroma.

arteriotomy incision or needle puncture of an artery.

arteriovenous associated with an artery and a vein.

arteriovenous fistula the artificial connection of an artery to a vein to promote the enlargement of the latter, to facilitate the removal and replacement of blood during haemodialysis.

arteriovenous shunt the direct connection between an artery and a vein.

arteritis an inflammatory disease affecting the media (middle) layer of arteries. It may be due to an infection such as syphilis or it may be part of a collagen disease. The arteries may become swollen and tender and the blood may clot in them.

artery a vessel carrying blood from the heart to the various tissues. The internal endothelial lining provides a smooth surface to prevent clotting of blood. The middle layer of plain muscle and elastic fibres allows for distension as blood is pumped from the heart. The outer, mainly connective tissue layer prevents overdistension. The lumen is largest nearest to the heart; it gradually decreases in size.

artery forceps forceps used to produce the arrest of bleeding or the slowing of blood flow (haemostasis).

arthralgia (articular neuralgia, arthrodynia) pain in a joint, used especially when there is no inflammation. Intermittent or periodic arthralgia is the term used when there is pain, usually accompanied by swelling of the knee at regular intervals.

arthritis inflammation of one or more joints which swell, become warm to touch, and are tender and painful on movement. There are many causes and the treatment varies according to the cause. See also gout, osteoarthritis, rheumatoid arthritis, Still’s disease.

arthroclasis breaking down of adhesions within the joint cavity to produce a wider range of movement.

arthrodesis the stiffening of a joint by surgical means.

arthrodynia painful joints. See also arthralgia.

arthrography a radiographic examination to determine the internal structure of a joint, outlined by contrast agent – either a gas or a liquid contrast agent, or both.

arthrology the science that studies the structure and function of joints, their diseases and treatment.

arthropathy any joint disease. The condition is currently classified as: enteropathic arthropathies resulting from chronic diarrhoeal disease; psoriatic arthropathies psoriasis; seronegative arthropathies include all other instances of inflammatory arthritis other than rheumatoid arthritis; seropositive arthropathies include all instances of rheumatoid arthritis.

arthroplasty surgical remodelling of a joint, replacement arthroplasty of the hip, insertion of an inert prosthesis of similar shape, total replacement arthroplasty of the hip, replacement of the head of femur and the acetabulum, both being cemented into the bone.

arthroscope an instrument used for the visualization of the interior of a joint cavity.

arthroscopy the act of visualizing the interior of a joint. Uses an intra-articular camera to assess, repair or reconstruct various tissues within and around joints.

arthrosis degeneration in a joint.

arthrotomy incision into a joint.

articular associated with a joint or articulation. Applied to cartilage, surface, capsule, etc.

articulation the junction of two or more bones; a joint. Enunciation of speech.

artificial anus see colostomy.

artificial blood a fluid able to transport O₂.

artificial kidney see dialyser.

artificial limb see orthosis, prosthesis.

artificial lung see respirator.

artificial menopause an earlier menopause caused by surgery or radiotherapy.

artificial pacemaker cardiac pacemaker. See also cardiac.

artificial pneumothorax see pneumothorax.

artificial respiration see cardiopulmonary resuscitation.

asbestos a fibrous, mineral substance which does not conduct heat and is incombustible. It has many uses, including brake linings, asbestos textiles and asbestos-cement sheeting.

asbestosis a form of pneumoconiosis from inhalation of asbestos dust and fibre. See also mesothelioma.

ascariasis infestation by nematodes (roundworms). The ova are ingested and hatch in the duodenum. The larvae pass to the lungs in the blood, from where they ascend to be swallowed and returned to the bowel. They may occasionally obstruct the intestine or the bile ducts.

Aschoff’s nodules nodules present in the myocardium in myocarditis caused by rheumatic fever.

ASCII (American Standard Code for Information Interchange) defines the decimal and binary code of all the characters stored in a computer.

ascites (hydroperitoneum) free fluid in the peritoneal cavity, well demonstrated by using ultrasound.

asepsis the condition of being free from living pathogenic micro-organisms.

aseptic technique describes procedures used to exclude pathogenic microorganisms from an environment. It includes the use of sterile gloves and gowns in theatre, non-touch technique and the use of sterilized equipment. Used where there is a possibility of introducing microorganisms into the patient’s body.

Askin tumour highly malignant tumour of the chest wall.

asomatogosia loss of awareness of parts of the body (soma) and their position in space, a perceptual sequela of cerebrovascular accident (stroke) affecting the right parietal lobe of the cerebrum, which may lead to lack of awareness, even denial, of the presence of disability.

asparaginase an enzyme derived from microorganisms. In the form of crisantaspase, used pharmacologically to treat cancers, for example, acute lymphoblastic leukaemia. See also cytotoxic.

asparagine a conditionally essential (indispensable) amino acid.

aspartate (aspartic acid) a non-essential (dispensable) amino acid.

Asperger’s syndrome a pervasive developmental disorder sharing characteristics with autism, without delayed language or cognitive development. The relationship of Asperger’s syndrome to autism remains unclear.

aspergillosis opportunist infection, most frequently of lungs, caused by any species of Aspergillus. See also bronchomycosis.

Aspergillus a genus of fungi, found in soil, manure and on various grains. Some species are pathogenic.

asphyxia a deficiency of oxygen in the blood and an increase in carbon dioxide in the blood and tissues. Common causes are drowning, electric shock, a foreign body in the air passages, inhalation of smoke or poisonous gasses, trauma or disease of the lungs or air passages.

aspiration (paracentesis, tapping) the removal of fluids from a body cavity by means of suction or siphonage such as fluid from the peritoneal cavity, postoperative gastric aspiration, etc. Describes the entry of fluids or food into the airway.

aspiration pneumonia inflammation of lung from inhalation of foreign body, most often food particles or fluids. See also Heimlich’s manoeuvre.

aspirator a negative pressure device used for withdrawing fluids from body cavities.

assault threat of unlawful contact. Constitutes trespass against the person. See also battery.

assay a quantitative test used to measure the amount of a substance present or its level of activity, for example, hormones or drugs. The analysis of the purity or effectiveness of a substance.

assimilation the process whereby digested foodstuffs are absorbed and used by the cells and tissues.

assisted conception techniques used when normal methods of conception have failed. They include in vitro fertilization (IVF) and transcervical embryo transfer or gamete intrafallopian tube transfer (GIFT), zygote intrafallopian transfer (ZIFT), preimplantation genetic diagnosis (PGD) and intracytoplasmic sperm injection (ICSI).

asthenia lack of strength; weakness, debility.

asthma gasping for breath, wheezing and difficulty in expiration because of muscular spasm in the bronchi. Inhaled or oral corticosteroids reduce the acute immune reaction, while inhaled β₂ receptor-agonists relieve bronchial spasm.

astigmatism light from one point not focussing on another point.

astringent describes an agent which contracts organic tissue, thus lessening secretion. May be used in the management of heavily exuding wounds.

astrocyte a star-shaped neuroglial cell.

astrocytoma a slowly invasive primary tumour of the brain.

asymmetry lack of similarity of the organs or parts on each side.

asymptomatic symptomless.

asystole absence of heart beat. One type of cardiac arrest.

ataxia (ataxy) failure of voluntary muscle coordination resulting in irregular jerky movements and unsteadiness.

atelectasis numbers of pulmonary alveoli do not contain air due to failure of expansion (congenital atelectasis) or resorption of air from the alveoli (collapse).

atheroma fatty deposits in an artery wall.

atherosclerosis coexisting atheroma and arteriosclerosis.

athletic trainer a term used in North America for an individual who is trained in the prevention, evaluation, treatment and rehabilitation of athletic injuries.

atlanto-axial joint a joint between the odontoid process of the axis (second cervical vertebra) and a facet on the arch of the atlas (the first cervical vertebra).

atlas the first cervical vertebra.

ATM (Asynchronous Transfer Mode) a computer circuit which is made when a computer is connected to the internet to enable the transfer of data at speeds of up to 155 Mb/s.

atom a particle with a nucleus which contains protons which carry a positive charge, surrounded by orbiting electrons which carry a negative charge. The smallest particle of an element capable of existing individually, or in combination with one or more atoms of the same or another element.

atomic mass number (A) the total number of nucleons in the nucleus of an atom.

atomic mass unit (amu) or Dalton a relative weight used to measure atoms and subatomic particles. Protons and neutrons have both been designated as being 1 amu. atomic number the number of protons in the atomic nucleus or the number of electrons, such as hydrogen which, with one of each, has the atomic number 1.

atomic number (Z) the number of protons in the nucleus of an atom.

atomic weight (mass) (or relative atomic mass) the relative average mass of an atom based on the mass of an atom of carbon-12.

atomizer nebulizer.

atonia total flaccidity or no muscle tone caused by complete loss of motor supply to a muscle.

atopic dermatitis that variety of infantile eczema that may be associated with asthma or hay fever.

atopic syndrome a hereditary predisposition to develop hypersensitivity disorders, such as eczema, asthma, hay fever and allergic rhinitis. Associated with excess IgE production.

atresia closure, or lack of a normal body opening, duct or canal such as the bowel or bile duct.

atrial fibrillation a cardiac arrhythmia. Chaotic irregularity of atrial rhythm with an irregular ventricular response. Commonly associated with mitral stenosis, hyperthyroidism (thyrotoxicosis) or heart failure.

atrial flutter a cardiac arrhythmia caused by irritable focus in atrial muscle and usually associated with coronary heart disease. Speed of atrial beats is between 260 and 340 per minute. The ventricular response is slower and may respond to every four atrial beats.

atrial septal defect a hole in the atrial septum. Most commonly due to a congenital defect. Types include: ostium secundum defect, which is most common and is situated around the site of the foramen ovale; and ostium primum defects situated lower down on the atrial septum.

atrioventricular (A-V) associated with the atria and the ventricles of the heart. Applied to a node, tract and valves.

atrioventricular bundle part of the conducting system of the heart. Carries impulses from the atrioventricular node to the ventricles. Divides into right and left bundle branches that transmit the impulses to the apex of each ventricle. atrioventricular node part of the conducting system of the heart. Situated at the bottom of the right atrium, it transmits impulses from the sinus node to the atrioventricular bundle. Also known as the bundle of His.

atrium cavity, entrance or passage. One of the two upper receiving chambers of the heart.

atrophy loss of substance of cells, tissues or organs. There is wasting and a decrease in size and function. The process may be physiological such as that occurring as part of normal ageing, or pathological, as in disuse atrophy when a limb is immobilized. See also motor neuron disease.

atropine the principal alkaloid of belladonna.

attachment a document sent with an e-mail. In psychology a term describing the dependent relationship which one individual forms with another, emanating from the unique bonding between infant and parent figure.

attenuation absorption. The process by which pathogenic micro-organisms are induced to develop or show less virulent characteristics, they can then be used in the preparation of vaccines. It is a measure of the absorption of an X-ray beam along a specific path through a substance. Of ultrasound at diagnostic frequencies, attenuation is approximately proportional to frequency, with the higher frequencies being absorbed more than the lower frequencies, the weakening of ultrasound as it goes through tissue due to absorption, reflection and scattering of the sound wave, measured in decibels. See also linear attenuation coefficient.

attenuation coefficient is a measure of the attenuation of an X-ray beam along a specific path through a substance. See also linear attenuation coefficient.

atypical not typical; unusual, irregular; not conforming to type, for example, atypical pneumonia.

audiology the scientific study of hearing.

audit investigative methods used to systematically measure outcomes and review performance. See also medical audit.

Audit Commission within the NHS the main role of the Audit Commission is to promote ‘best practice’ in terms of economy, effectiveness and efficiency.

audit trail a way of working and record keeping that allows the processes to be transparent and clear.

auditory associated with the sense of hearing.

auditory acuity ability to hear clearly and distinctly. Tests include the use of tuning fork, whispered voice and audiometer. Hearing can be tested in babies by otoacoustic emission testing (OAE).

auditory area that portion of the temporal lobe of the cerebral cortex which interprets sound.

auditory canal (external auditory meatus) the canal between the pinna and eardrum.

auditory nerves the eighth pair of cranial nerves. Also called the vestibulocochlear nerve.

auditory ossicles three small bones – malleus, incus and stapes – located within the middle ear.

auger electrons are ejected during radioactive decay and have discrete energy levels equal to the photon energy minus the binding energy of the electron.

aura a premonition; a peculiar sensation or warning of an impending attack, such as occurs in epilepsy or migraine.

aural associated with the ear.

auricle the pinna of the external ear. An appendage to the cardiac atrium. Obsolete term for atrium.

auricular ear shaped.

auricular line a line perpendicular to the anthropological base line through the centre of the external auditory meatus. See also anthropological base line.

auriculoventricular obsolete term. See atrioventricular.

auriscope see otoscope.

auscultation

examination of the internal organs by listening to the sounds they produce.

autoantibody an antibody which binds self-antigen expressed in normal tissue.

autoantigen a self-antigen, expressed in normal tissue, which is the target of autoantibodies or self-reactive T cells.

autoclave apparatus for high-pressure steam sterilization, to sterilize in an autoclave.

autodigestion self-digestion of body tissue during life.

autogenic describes a process or condition that originates from within the organism.

autogenic facilitation reflex activation of a muscle through activation of its own sensory receptors; self-generated excitation of muscle, for example, the stretch reflex.

autogenic inhibition reflex inhibition of a muscle through activation of stretch receptors, the Golgi tendon organs, in its own tendons; self-generated relaxation of muscle that normally prevents build-up of too much, potentially injurious, tension in a muscle.

autogenic therapy a complementary therapy that employs a combination of self-hypnosis and relaxation.

autograft tissue grafted from one part of the body to another.

autoimmune disease an illness caused by, or associated with, the development of an immune response to normal body tissues.

autoimmunity the production of antibodies against the subjects own tissue.

autoinfection self-infection or pathogens transferred from one part of the body to another, for example by the hands or towels etc.

autointoxication poisoning from abnormal or excessive metabolic products produced in the body, some of which may originate from infected or necrotic tissue.

autologous when a patient acts as the source of cells. This may include a patient donating blood or blood products prior to elective surgery to be transfused postoperatively. Cross-matching and compatibility problems are avoided, as is the risk of blood-borne infections.

autologous bone marrow transplant when a patient is in remission their bone marrow or peripheral blood stem cells are harvested and then reinfused to reinforce the bone marrow. May be performed for patients with leukaemia. Their bone marrow or peripheral blood stem cells are harvested, stored and replaced after leukaemic cells have been destroyed with cytotoxic chemotherapy or radiotherapy.

autologous implants implants using tissue obtained from the same patient.

automated peritoneal dialysis (APD) a type of peritoneal dialysis where the fluid exchanges are performed at night by the use of a mechanical device.

automatic occurring without the influence of the will; spontaneous; without volition; involuntary acts.

automatic chemical mixers equipment to mix the processing chemicals used to minimize the handling of chemicals by the staff, to promote even mixing and reduce chemical fumes.

automatic shuttering in digital imaging, the automatic blackening of the film outside the collimated image to increase the subjective contrast of the image. See also subjective contrast.

autonomic independent; self-governing.

autonomic nervous system (ANS) is divided into parasympathetic and sympathetic portions. They are made up of nerve cells and fibres which cannot be controlled at will. They are concerned with the control of glandular secretion and involuntary muscle.

autopsy the examination of a dead body (cadaver) for diagnostic purposes.

autosome in humans one of 44 (22 pairs) non-sex chromosomes. The full chromosome complement of 46 (23 pairs) found in somatic cells comprises 44 autosomes and two sex chromosomes.

autosomal inheritance is determined by the expression or not of genes on the autosomes. It may be dominant or recessive.

autotransformer a type of transformer where the primary and secondary coils are wound round a single core; it is used when only low-voltage changes are required.

avascular bloodless; not vascular, i.e. without blood supply.

avascular necrosis death of tissue due to complete depletion of its blood supply. Usually applied to that of bone tissue following injury or possibly through disease. Commonly seen with fractures of the femoral neck, leading to death of the femoral head. Also seen in scaphoid and head of humerus fractures. Often a precursor of osteoarthritis.

average dose in radiotherapy the value of dose calculated by adding together all the individual radiation doses in the area and then dividing the total by the number of doses.

average gradient a method of measuring the straight line portion of a characteristic curve to determine the contrast of a film. A right angle triangle is drawn on the characteristic curve with the hypotenuse of the tri-angle extending from density 0.25 and 2 on the straight line portion of the curve. The angle between the hypotenuse and the horizontal line of the triangle is calculated, therefore the tangent of the angle the slope makes equals the average gradient. See also contrast.

averaging a method of improving the signal-to-noise ratio in magnetic resonance imaging. The same magnetic resonance signal is added up and the total is divided by the number of signals.

avian relating to birds.

avian tuberculosis is caused by Mycobacterium avium complex (MAC) or M. avium-intracellulare (MAI), which also cause atypical tuberculosis in humans, especially in immunocompromised individuals.

avitaminosis any disease resulting from a deficiency of vitamins.

Avogadro’s number is 6 ÷ 10²³ molecules which is the number of molecules in a mole.

avulsion a forcible wrenching away of a structure or part of the body.

avulsion fracture a fracture caused by the tearing away of a fragment of bone by a ligament or tendon.

axes the vertical (y axis) and horizontal (x axis) lines on a graph.

axial projection a radiograph taken when either a joint is flexed and/or the beam angled.

axial resolution in ultrasound, the ability to see small structures along the beam; this is dependent on the pulse length which is determined by the wavelength. When the distance between two reflecting surfaces of the object is half the pulse length or less the object will not be demonstrated.

axial skeleton the bones forming the head and trunk.

axilla the armpit.

axillary applied to nerves, blood and lymphatic vessels, of the axilla.

axis the second cervical vertebra. An imaginary line passing through the centre; the median line of the body.

axon the long process of a nerve cell conveying impulses away from the cell body.

axonotmesis (neuronotmesis, neurotmesis) peripheral degeneration as a result of damage to the axons of a nerve, through pinching, crushing or prolonged pressure. The internal architecture is preserved and recovery depends upon regeneration of the axons, and may take many months.

axon reflex reflex dilatation of the arterioles occurring when sensory nerves in the skin are stimulated by massage manipulations or trauma.

azoospermia absence of spermatozoa in the semen.

azygos occurring singly, not paired.

azygos veins three unpaired veins of the abdomen and thorax which empty into the inferior vena cava.

Churchill Livingstone Pocket Radiography and Medical Imaging Dic