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.
Regions of the abdominal cavity.
From Ross and Wilson’s anatomy and physiology in health and illness, 9th edn, Anne Waugh and Alison Grant (eds), 2001, Churchill Livingstone, Edinburgh, with permission.
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.
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).
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 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.
acystia congenital absence of the bladder.
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.
aerophagia (aerophagy) excessive air swallowing.
aetiology (etiology) the study of the cause of disease.
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.
