H
habitual abortion see miscarriage.
haem the iron-containing pigment portion of haemoglobin.
haemangioma a benign tumour formed by dilated blood vessels which may occur in any part of the body. When in the skin it is one form of birthmark, appearing as a red spot or a ‘port wine stain’.
haemarthrosis the presence of blood in a joint cavity.
haematemesis the vomiting of blood, which may be bright red following recent bleeding – or ‘coffee ground’ appearance if it has been in the stomach for some time. The bleeding is usually from the upper gastrointestinal tract and causes include peptic ulcer, varices, neoplasms, drug erosions and coagulation defects.
haematin a ferric-iron-containing derivative of haemoglobin.
haematinic a substance required for the production of red blood cells.
haematocele a swelling filled with blood.
haematogenous originating or transported by the blood.
haematoma a swelling composed of blood which can occur in any part of the body.
haematometra an accumulation of blood (or menstrual fluid) in the uterus.
haematuria blood in the urine; may be macroscopic, i.e. visible to the naked eye, microscopic when it is not.
haemoccult test a test to detect minute quantities of blood in the faeces.
haemodialysis a procedure in which impurities or wastes are removed from the blood. A method of renal replacement therapy used in patients in end-stage renal disease/failure (irreversible) or in acute renal failure (potentially reversible). The patient’s blood is shunted from the body through a machine for diffusion and filtration and then returned to the patient’s circulation. The procedure takes from 3–8 hours and may take place daily or two or three times a week.
haemodynamics the study of blood circulation.
haemofiltration (CVVH) form of renal replacement therapy (artificial kidney treatment), in which the patient’s blood is passed through a filter allowing separation of an ultrafiltrate containing fluid and solutes. This is discarded and replaced with an isotonic solution. Usually continuous as in continuous veno-venous haemofiltration.
haemoglobin (Hb) the red, respiratory pigment in the red blood cells. A molecule comprises four ferrous-iron-containing haem groups and four globin chains. It combines with oxygen and releases it to the tissues. Some carbon dioxide is carried by haemoglobin, which also acts to buffer pH changes. There is a special form of fetal haemoglobin (HbF) which has a high affinity for oxygen, and two major adult forms (HbA, HbA2). HbF is replaced by adult forms during early childhood. See also oxyhaemoglobin.
haemoglobinopathy usually hereditary abnormality of the haemoglobin molecule.
haemoglobinuria haemoglobin in the urine.
haemolysin an agent capable of causing disintegration of red blood cells.
haemolytic anaemia a condition caused by the premature destruction of red blood cells, as with some drugs and toxins, autoimmune processes, or inherited red cell disorders.
haemolytic disease of the newborn (erythroblastosis fetalis) a pathological condition in the newborn child due to Rhesus incompatibility between the child’s blood and that of the mother. Red blood cell destruction occurs with anaemia, often jaundice and an excess of erythroblasts or primitive red blood cells in the circulating blood. Immunization of women at risk, using anti-D immunoglobulin, can prevent haemolytic disease of the newborn. Treatment of affected infants may include phototherapy, blood transfusion and exchange transfusion in severe cases.
haemoperitoneum blood in the peritoneal cavity.
haemophilias a group of conditions with inherited blood coagulation efects. In clinical practice the most commonly encountered defects are aemophilia A (factor VIII procoagulant deficiency) and haemophilia B or Christmas disease (factor IX procoagulant deficiency). Both of these conditions are X-linked recessive disorders resulting in an increased tendency to bleed, the severity of which depends on the amount of residual factor VIII or IX. Bleeding typically occurs into joints and muscles. See also haemophilic arthropathy.
haemophilic arthropathy joint disease associated with haemophilia. The extent of joint damage has been ‘staged’ from radiological findings: (a) synovial thickening, (b) epiphyseal overgrowth, (c) minor joint changes and cyst formation, (d) definite joint changes with loss of joint space, (e) end-stage joint destruction and secondary changes leading to deformity.
haemopneumothorax the presence of blood and air in the pleural cavity.
haemopoiesis (haematopoiesis) the formation of blood. See also erythropoiesis.
haemoptysis the coughing up of blood which is bright red in colour and frothy. May be as a result of carcinoma of the bronchus, pulmonary tuberculosis, bronchiectasis.
haemorrhage loss of blood from a vessel. Usually refers to serious rapid blood loss. This may lead to hypovolaemic shock with tachycardia, hypotension, rapid breathing, pallor, sweating, oliguria, restlessness and changes in conscious level. Haemorrhage can be classified in several ways: (a) according to the vessel involved: arterial, venous or capillary; (b) timing: primary haemorrhage occurs at the time of injury or operation, reactionary haemorrhage occurs within 24 hours of injury or operation, secondary haemorrhage occurs within some days of injury or operation and usually associated with sepsis; (c) whether it is internal (concealed) or external (revealed).
haemorrhagic periostitis inflammation of the periosteum accompanied by bleeding between the periosteum and the bone.
haemorrhoids (piles) dilated veins around the anus. external haemorrhoids those outside the anal sphincter, covered with skin. internal haemorrhoids those inside the anal sphincter, covered with mucous membrane.
haemosiderin an iron–protein complex. A storage form of iron.
haemospermia blood in the semen.
haemostasis the process that controls bleeding from small vessels. Damage to the blood vessels starts a complex series of reactions between substances in the blood and others released from damaged platelets and tissue. There are four overlapping stages: vasoconstriction, platelet plug formation, coagulation and fibrinolysis. Also includes the measures used to stop bleeding during surgery or following injury.
haemothorax blood in the pleural cavity usually associated with chest injuries, for example fractured ribs.
halation the reflection back of light after it passes through a radiographic emulsion which may then re-expose the emulsion causing unsharpness on the film.
half-life amount of time taken for the radioactivity of a radioactive substance to decay by half the initial value. The half-life is a constant for each radioactive isotope, e.g. iodine-131 is 8 days. Or the time taken for the concentration of a drug in the plasma to fall by half the initial level. biological half-life time taken by the body to eliminate 50% of the dose of any substance by normal biological processes. effective half-life time taken for a combination of radioactive decay and biological processes to reduce radioactivity by 50%.
half-speed emulsion has half the speed of standard radiographic emulsions with an increase in image quality but also an increase in patient dosage. See also standard contrast emulsion.
half-value thickness the thickness of a substance that will transmit exactly one-half of the intensity of radiation falling on it.
hallucinations a false perception occurring without any true sensory stimulus.
hallucinogens chemicals that cause hallucinations.
hallux rigidus ankylosis of the metatarsophalangeal articulation due to osteoarthritis.
hallux valgus (hallux abducto-valgus, bunion) a complex deformity of the medial column of the foot involving abduction and external rotation of the great toe and adduction and internal rotation of the first metatarsal (referenced to the midline of the body). Deformity exists when abduction of the hallux on the metatarsal is greater than 10 to 12°. Friction and pressure of shoes cause a bursa to develop. The prominent bone, with its bursa, is known as a bunion.
hallux varus the great toe deviates toward the midline of the body and is commonly seen with metatarsus adductus.
halopelvic traction a form of external fixation whereby traction can be applied to the spine between two fixed points. The device consists of three main parts (a) a halo, (b) a pelvic loop, and (c) four extension bars.
hamate one of the eight carpal bones of the wrist.
hammer toe a permanent hyperextension of the first phalanx and flexion of second and third phalanges.
hamstring muscles flexor muscles of the posterior part of the thigh.
hamulus a hook-like projection.
hand that part of the upper limb below the wrist.
handshake an electronic signal which indicates the end of the passage of data from the computer.
hard copy the paper printout of the program or screen display.
hard rollers part of the radiographic film transport system in an automatic processor made of paper wound round a stainless steel core and impregnated with epoxy resin.
hardener an addition to the radiographic film emulsion to make it resistant to abrasions, an addition to the developer and the fixer to reduce mechanical damage and sticking of the films to the racks.
hard palate the front part of the roof of the mouth formed by the two palatal bones.
hardware the mechanical and electronic part of the equipment.
Harrington rod a ridged, contoured, metal rod, surgically inserted, along with metal hooks, into the posterior aspect of the spine to treat scoliosis and other deformities.
Hashimoto’s thyroiditis a disease of the thyroid when the normal structures are replaced with lymphocytes and lymphoid germinal centres producing a goitre.
haustration small pouches (sacculation), as of the colon.
haversian system a cylindrical system found in compact bone. Comprises lamellae, lacunae, Volkmann’s canals and canaliculi.
Hawthorne effect a positive effect occurring from the introduction of change, of which people are less aware as time passes. Researchers doing observation research make allowances for this reaction to their presence by not including data from the first few days in the final data analysis.
head injury injury resulting from a blow to the head causing haemorrhage or contusion. See also extradural haematoma.
healing the natural process of cure or tissue repair. See also wound healing. In complementary or integrated medicine the term healing refers to a return to health; also the use of a therapy that may assist the healing process; a specific therapeutic form, such as spiritual healing and thera-peutic touch.
healthcare systems national or local organizations for providing medical/health care. The structure of the system has to accommodate progress in medical interventions, consumer demand and economic efficiency. Criteria for a successful system have been formulated: (a) adequacy and equity of access to care, (b) income protection (for patients), (c) macro-economic efficiency (national expenditure measured as a proportion of gross domestic product), (d) micro-economic efficiency (balance of services provided between improving health outcomes and satisfying consumer demand), (e) consumer choice and appropriate autonomy for care providers. There are four basic types of healthcare systems: socialized (UK NHS), social insurance (Canada, France), mandatory insurance (Germany), voluntary insurance (USA).
Health Development Agency a statutory body set up to improve standards in public health. It is concerned with identifying the need for evidence and for commissioning research. Other roles include: standard setting, undertaking health promotion campaigns and distributing examples of good practice.
health gain an attempt at measuring the benefit of health intervention on the population. For example, health gain from a cervical cytology screening programme may be measured as the reduction in deaths from cervical cancer; coronary heart disease prevention programme measured as a reduction in deaths from coronary heart disease in men under 65 years of age, or the number of deaths avoided over a specified period of time (e.g. 5 years).
Health Improvement Programme (HImP) a focused action plan for improving health and healthcare provision at a local level. Involves a collaborative approach between Primary Care Trust(s), health professionals, local government, voluntary organizations and patient groups, etc.
health informatics the process of using a computer to manage information.
health level 7 the international standard for textual communication of electronic data in and between any healthcare environment.
Healthlink a centralized, data communications network for healthcare professionals which enables authorized users to exchange documents and information cheaply and efficiently.
health promotion efforts to prevent ill health and promote positive health. Five key priority areas for action formulated by the World Health Organization (1986, 1998): (a) building healthy public policy, (b) creating supportive environments for health, (c) strengthening community action for health, (d) developing personal skills for health and (e) re-orientating health services (to focus on whole populations).
hearing impaired a loss or reduction of hearing.
heart the hollow muscular organ which pumps the blood around the pulmonary and general circulations. It is situated behind the sternum, lying obliquely within the mediastinum. It weighs approximately 300g and is about the size of the person’s fist. heart block partial or complete block to the passage of impulses through the conducting system of the atria and ventricles of the heart.
heart failure see congestive heart failure.
heart transplant surgical transplantation of a heart from a suitable donor.
heartburn retrosternal burning due to gastro-oesophageal reflux of acid.
heart–lung machine a machine that bypasses both the heart and lungs and may be used in cardiac surgery to oxygenate the blood.
heat exchanger a method of maintaining the temperature of solutions in an automatic film processor with a series of separate tubes through which water, developer or fixer flows; any waste heat from the developer is absorbed and passed to the water or heat from the water can be absorbed from the fixer.
Heberden’s nodes small bony swelling at terminal (distal) interphalangeal joints occurring in osteoarthritis.
heel bruise (stone bruise) contusion to the subcutaneous fat pad located over the inferior aspect of the calcaneus.
heel spurs occur on the plantar surface of the calcaneus and are consid-ered a variant of the normal point of attachment of the plantar fascia. They are insignificant when small, and may be well defined with smooth, regular cortical contours. However, when enlarged they cause pain on walking.
Heimlich 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.
helium–neon laser a laser which has helium-neon gas in the tube and produces red light.
helix spiral. Outer ridge on the auricle (pinna) of the outer ear. Describes the structure of molecules such as DNA.
hemiatrophy atrophy of one half or one side. See also facial hemiatrophy.
hemibody half or on one side of the body.
hemiglossectomy removal of approximately half the tongue.
hemiparesis paralysis or weakness of one side of face or body.
hemiplegia paralysis of one side of the body, usually resulting from a cerebrovascular accident on the opposite side.
hemiplegic a patient paralysed down one side.
hepatic associated with the liver.
hepatic portal circulation that of venous blood (collected from the intestine, pancreas, spleen and stomach) to the liver before return to the heart.
hepaticoenteric associated with the liver and intestine.
hepatocellular associated with or affecting liver cells.
hepatoma primary carcinoma of the liver.
hepatomegaly enlargement of the liver. It is palpable below the costal margin.
hepatosplenic associated with the liver and spleen.
heredity transmission from parents to children of genetic characteristics by means of the genetic material; the process by which this occurs, and the study of such processes.
hermaphrodite individual possessing both ovarian and testicular tissue. Although they may approximate either to male or female type, they are usually sterile from imperfect development of their gonads.
hernia the abnormal protrusion of an organ, or part of an organ, through an aperture in the surrounding structures: commonly the protrusion of an abdominal organ through a gap in the abdominal wall. See also femoral hernia, hiatus hernia, incisional hernia, inguinal hernia, irreducible hernia, strangulated hernia, umbilical hernia.
herpes simplex a viral infection resulting in an inflammatory skin eruption.
hertz (Hz) a SI unit (International System of Units) for wave frequency. One hertz equals one cycle per second.
heterogeneous consisting of dissimilar elements or parts; unlike, not being uniform throughout. See also homogeneous.
heterosexual of different sexes; often used to describe an individual who is sexually attracted to members of the opposite sex. See also homosexual.
heuristic a ‘trial and error’ method of trying to solve a computer problem.
hexadecimal a mathematical system which employs 16 digits from 0 to 9 plus A, B, C, D, E, F. For example, hexadecimal 24A is equal to decimal 570.
Comparison of decimal, hexadecimal and binary number systems 0–20a
| Decimal | Hexadecimal | Binary |
|---|---|---|
| 0 | 0 | 0 |
| 1 | 1 | 1 |
| 2 | 2 | 10 |
| 3 | 3 | 11 |
| 4 | 4 | 100 |
| 5 | 5 | 101 |
| 6 | 6 | 110 |
| 7 | 7 | 111 |
| 8 | 8 | 1000 |
| 9 | 9 | 1001 |
| 10 | A | 1010 |
| 11 | B | 1011 |
| 12 | C | 1100 |
| 13 | D | 1101 |
| 14 | E | 1110 |
| 15 | F | 1111 |
| 16 | 10 | 10000 |
| 17 | 11 | 10001 |
| 18 | 12 | 10010 |
| 19 | 13 | 10011 |
| 20 | 14 | 10100 |
a From Radiographic imaging, 3rd edn, 2002, Chris Gunn, Churchill Livingstone, Edinburgh, with permission.
hiatus hernia movement of part of the stomach through the diaphragmatic hiatus into the chest. May be asymptomatic, cause gastro-oesophageal reflux or strangulate. See also hernia.
high-dependency unit (HDU) an area within a hospital with augmented levels of staff and equipment in which patients can receive levels of obser-vation monitoring, nursing and medical care between that available on a general ward and intensive care unit. Generally excludes those needing mechanical ventilation.
high-resolution CT a method of using thinner slices in CT scanning in order to increase the image definition.
high spatial frequency algorithm in CT scanning an algorithm used to provide high spatial resolution. Frequently used to demonstrate bone, or in high resolution chest studies. See also algorithm.
high-temperature chemistry the chemistry used in automatic radiographic processing equipment that function in the range of 31–39°C at a pH of about 9.6, now superseded by low-temperature chemistry. See also low-temperature chemistry.
hilum a depression on the surface of an organ where vessels, ducts, etc. enter and leave.
hinge angle the angle between two radiotherapy beam axes at their point of intersection.
hinge joint a synovial joint that allows only flexion and extension, for example, the elbow joint.
hip bone (innominate bone) formed by the fusion of three separate bones, the ilium, ischium and pubis.
hip joint a synovial ball and socket joint formed by the acetabulum of the pelvis and the head of femur.
Hirschsprung’s disease congenital intestinal absence of a ganglia (aganglionosis), leading to intractable constipation or even intestinal obstruction. There is marked hypertrophy and dilation of the colon (megacolon) above the aganglionic segment. Commoner in boys and children with Down’s syndrome.
HIS (hospital information system) a computerized system, the aim of which it to build a network of complementary centres, for example, hospitals, laboratories, primary care trusts and GP centres, etc. spread throughout Europe, to meet the social and healthcare needs in each area. The term can also be used to define the system used in an individual hospital or unit.
histamine a compound found in all cells which is released in allergic, inflammatory reactions and causes dilation of capillaries, decrease in blood pressure, increase in secretions of gastric juice and a constriction of smooth muscle of the bronchi and uterus. See also allergy, anaphylaxis, inflammation.
histamine receptors there are three types in the body, H1 in the bronchial muscle, H2 in the secreting cells in the stomach and H3 in nerve tissue.
histamine test test previously used to determine the maximal gastric secretion of hydrochloric acid.
histiocytes macrophages or phagocytic tissue cells.
histiocytoma benign tumour of histiocytes.
histogram a graph displaying data in columns which are next to each other.
histology microscopic study of tissues.
Hodgkin’s disease tumour of lymphoid tissue often originating in the mediastinum. Often occurs in young adults. A diagnostic feature is the presence of the large multinucleated Reed–Sternberg cells in the lymphatic system. The prognosis is related to the histological subtype and stage; cure rate is about 80%. Treatment may consist of radiotherapy and/or chemotherapy. See also lymphoma.
holes the absence of an electron in the valence band, the ‘hole’ has a positive charge and therefore can attract electrons.
holistic relating to the theory of holism. Describes health care that takes account of physical, psychological, emotional, social and spiritual aspects.
home-care team nurses trained in palliative care who provide additional support in a patient’s home.
homeostasis autoregulatory processes whereby functions such as blood pressure, blood glucose and electrolytes are maintained within set parameters.
homogeneous of the same type; of the same quality or consistency throughout.
homogenize to make into the same consistency throughout.
homogenous having a like nature; for example, a bone graft from another human being.
hoop traction fixed skin traction used for the treatment of fractures of the femoral shaft in children, and for the gradual abduction of the hip in children with developmental dysplasia of the hip.
horizontal plane see transverse plane.
hormone a specific chemical messenger produced by endocrine glands that is transported in the blood or lymph to regulate the functions of tissues and organs elsewhere in the body.
horseshoe kidney an anatomical variation in which the inner lower border of each kidney is joined to give a horseshoe shape. Usually symptomless, but rarely interferes with drainage of urine into ureters.
hospice specialist centres that care for the terminally ill.
hospital-acquired infection (HAI, nosocomial infection) occurs in a patient who has been in hospital for at least 72 hours and did not have signs and symptoms of such infection on admission: 10–12% of hospital patients develop a HAI. Urinary tract infection is the most common type.
hospital sterilization and disinfection unit (HSDU) central sterile supply units (CSSUs) that also provide disinfection of equipment.
host computer the main computer in a system containing a number of computers.
hot spot a term used for the high uptake of a radionuclide in part of the body and thus indicating the presence of a lesion.
Hough transform a technique for electronically enhancing the edges of a feature in a digital image to improve its image quality.
Hounsfield unit a standardized unit for reporting and displaying reconstructed CT values. Water is given a nominal value of 0, other structures are reproduced with values relative to water. A change in one Hounsfield unit corresponds to 0.1% of the attenuation coefficient difference between water (0 HU) and air (–1000HU).
housemaid’s knee see bursitis.
HU the measure of heat energy deposited in the anode by an exposure and is the product of the kilovoltage peak and the milliampere per second.
hub a device for connecting computers together to form a network.
human chorionic gonadotrophin (HCG) a hormone produced by the trophoblast cells and later the chorion. A tumour marker for testicular and choriocarcinoma.
human immunodeficiency virus (HIV) currently designates the AIDS virus. There are two types: HIV-1 (many strains), mainly responsible for HIV disease in Western Europe, North America and Central Africa, and HIV-2, causing similar disease mainly in West Africa.
human leucocyte antigen (HLA) the major histocompatibility complexes, so called because they were first found on leucocytes.
human papilloma virus (HPV) there are many types of HPV, including several that are associated with anogenital warts (particularly types 6 and 11), and a few types (particularly 16 and 18) that are associated with genital tract malignancy such as cervical carcinoma.
human T-cell lymphotropic viruses (HTLV) two retroviruses; HTLV-1 and HTLV-2, both of which are linked with some forms of leukaemia.
humerus the bone of the upper arm, between the elbow and shoulder joint.
humour any fluid of the body. See also aqueous, vitreous.
Hurter and Driffield curve an alternative name for the characteristic curve of a radiographic film.
Hutchinson’s teeth defect of the upper central incisors (second dentition) which is part of the appearance of congenital syphilis. The teeth are broader at the gum than at the cutting edge, with the latter showing an elliptical notch.
Huygens’ principle when an ultrasound beam generated by a single source may be considered as the sum of the beams generated by a number of point sources.
hyaline like glass; transparent.
hyaline cartilage covers the ends of bones when forming a joint.
hyaline degeneration degeneration of connective tissue, especially that of blood vessels in which tissue becomes formless in appearance.
hyaloid resembling hyaline tissue.
hyaloid membrane the transparent capsule surrounding the vitreous humour of the eye.
hydatid cyst the cyst formed by larvae of a tapeworm, Echinococcus granulosa, found in dogs and other canines. The encysted stage normally occurs in sheep but can occur in humans after eating with soiled hands from contact with dogs or infected sheep. The cysts are commonest in the liver, but can affect the brain, lungs and bone.
hydatidiform associated with or resembling a hydatid cyst.
hydatidiform mole a condition of pregnancy when the chorionic villi of the placenta degenerate into a cluster of cysts which may become malignant. A complete hydatidiform mole shows abnormal proliferation of the trophoblast and the presence of hydropic placental villi with no fetal parts. An incomplete hydatidiform mole or partial mole has a chromosomally abnormal fetus (triploid chromosome complement). Malignant transformation to choriocarcinoma may occur, especially in pregnancies affected by a complete hydatidiform mole.
hydraemia a greater plasma volume than usual compared with cell volume of the blood; normally present in late pregnancy.
hydramnios an excess of amniotic fluid.
hydrarthrosis a collection of synovial fluid in a joint cavity.
hydrocele a swelling due to accumulation of serous fluid between the tunica vaginalis and tunica albuginea of the testis or in the spermatic cord.
hydrocephalus (‘water on the brain’) an excess of cerebrospinal fluid inside the skull due to a disruption in normal CSF circulation, or loss of brain tissue. See also external hydrocephalus, internal hydrocephalus.
hydrochloric acid acid formed from hydrogen and chlorine; secreted by the gastric oxyntic cells and present in gastric juice.
hydrogen (H) a colourless, odourless, combustible gas. hydrogen ion concentration (pH) a measure of the acidity or alkalinity of a solution, ranging from pH 0 to pH 14, 7 being approximately neutral; the lower numbers denote acidity, the higher ones denote alkalinity. hydrogen peroxide (H2O2) a powerful oxidizing and deodorizing agent, used in suitable dilution in mouthwashes.
hydronephrosis an accumulation of urine in the pelvis of the kidney, if unrelieved may result in atrophy of the kidney due to the obstruction of the flow of urine from the kidney. The obstruction may be caused by an obstruction of the ureter by a tumour or stone, it may be congenital or caused by the constriction of the urethra by an enlarged prostate gland.
hydropneumopericardium the presence of air and fluid in the pericardial sac surrounding the heart. It may accompany pericardiocentesis.
hydropneumoperitoneum the presence of air and fluid and gas in the peritoneal cavity: it may accompany paracentesis of that cavity; it may accompany perforation of the gut; or it may be due to infection with gas-forming microorganisms.
hydropneumothorax pneumothorax further complicated by effusion of fluid into the pleural cavity.
hydroquinone a radiographic developer agent.
hydrosalpinx distension of a uterine tube with watery fluid.
hydrostatic pressure that exerted by a liquid on the walls of its container, such as blood on an artery.
hydrothorax the presence of fluid in the pleural cavity. Also known as a pleural effusion.
hydroureter dilation of the ureter and renal pelvis.
hydroxyapatite the calcium salts, carbonate, hydroxide and phosphate, that make bone extremely hard.
hydroxyl (OH2) a monovalent ion, consisting of a hydrogen atom linked to an oxygen atom.
5-hydroxytryptamine (5-HT) a neurotransmitter. Also present in the gastrointestinal tract and platelets. Also known as serotonin.
hygiene the science dealing with the maintenance of health. communal hygiene embraces all measures taken to supply the community with pure food and water, good sanitation, housing, etc. industrial hygiene (occupational health) includes all measures taken to preserve the individual’s health while he or she is at work. mental hygiene deals with the establishment of healthy mental attitudes and emotional reactions. personal hygiene includes all those measures taken by the individual to preserve his or her own health.
hygroma a cystic swelling containing watery fluid, usually situated in the neck and present at birth, sometimes interfering with birth.
hymen a perforated membrane across the vaginal entrance. imperforate hymen a congenital condition.
hyoid a U-shaped bone at the root of the tongue.
hyperacusis increased sensitivity to sound.
hyperbaric oxygen term applied to gas at up to three times atmospheric pressure.
hyperbaric oxygen therapy a form of treatment in which a patient is entirely enclosed in a pressure chamber breathing 100% oxygen at greater than one atmosphere pressure. Used for patients with carbon monoxide poisoning, decompression sickness, etc.
hypercalcaemia excessive calcium in the blood usually resulting from bone resorption as occurs in hyperparathyroidism, metastatic tumours of bone, or Paget’s disease. It results in anorexia, abdominal pain, muscle pain and weakness. It is accompanied by hypercalciuria and can lead to nephrolithiasis.
hypercalciuria greatly increased excretion of calcium in the urine. Occurs in diseases which result in bone resorption. idiopathic hypercalciuria is the term used when there is no known metabolic cause. Hypercalciuria is of importance in the formation and development (pathogenesis) of kidney stones.
hypercholesterolaemia excessive cholesterol in the blood. Predisposes to atheroma and gallstones. Also found in hypothyroidism (myxoedema).
hyperextension overextension. Active or passive force which takes the joint into extension beyond its normal physiological range.
hyperflexion excessive flexion.
hyperfractionation the delivery of more than one dose of radiation a day over a period of time, the dose per fraction is lower compared with conventional fractionations resulting in an increase in the overall tumour dose.
hyperglycaemia increased blood glucose, usually indicative of diabetes mellitus or impaired glucose tolerance, but sometimes due to pathological stress, e.g. myocardial infarction.
hyperglycaemic coma occurs in diabetes if the disease is untreated or if insulin has been omitted.
hyperinsulinism elevated circulating levels of insulin due to pancreatic tumour, insulinoma, or factitious administration of hypoglycaemic agents; resulting in hypoglycaemia, which may lead to episodic coma, confusion or even mental health disturbance.
hyperkeratosis premalignant small warty nodules which may be due to sunlight, actinic or solar keratosis, tar or X-rays.
hyperkinesis excessive movement.
hypermobility excessive mobility. As in a joint that has an increase in the normal range of joint movement potentially leading to instability.
hypermotility increased movement, as peristalsis.
hypernephroma (Grawitz tumour) a malignant tumour of the kidney.
hyperostiosis thickening of the skull vault.
hyperparathyroidism overactivity of one or more parathyroid glands, usu-ally due to parathyroid adenoma, and resulting in elevated serum calcium levels; rarely results in parathyroid bone disease, osteitis fibrosa cystica; may be primary, or secondary/tertiary usually in response to chronic renal failure. See also hypercalcaemia, hypercalciuria, von Recklinghausen’s disease.
hyperpituitarism see acromegaly, Cushing’s disease, gigantism, hyperprolactinaemia.
hyperplasia increase in the size of an organ due to an increase in the number of cells contained in the organ.
hyperprolactinaemia elevation in circulating prolactin levels, sometimes due to stress; if pathological results in galactorrhoea, menstrual irregularity and subfertility; may be due to dopamine antagonists, such as metoclopramide or neuroleptic drugs, large, often non-functioning pituitary tumours, or prolactinomas.
hyperpyrexia body temperature above 40–41°C.
hypertension abnormally high blood pressure involving systolic and/or diastolic levels. There is no universal agreement on the upper limits of normal, especially with increasing age. Many cardiologists consider a resting systolic pressure of 140mmHg and/or a resting diastolic pressure of 90mmHg to be abnormal at age 20 years. Hypertension is considered to be a risk factor for the development of coronary heart disease. secondary hypertension may result from coarctation of the aorta, renal artery stenosis, renal disease, phaeochromocytoma, Cushing’s disease/syndrome, Conn’s syndrome, various drugs, such as oral contraceptives, NSAIDs, and the pre-eclampsia of pregnancy. See also portal hypertension, pulmonary hypertension.
hyperthermia very high body temperature. See also hyperpyrexia.
hyperthyroidism (thyrotoxicosis) condition due to excessive production of thyroid hormone (thyroxine, triiodothyronine), usually due to Graves’ disease, but also multiple or solitary toxic nodules, and resulting classically in anxiety, tachycardia, sweating, increased appetite with weight loss, and a fine tremor of the outstretched hands; much commoner in women than men.
hypertrophy increase in the size of tissues or structures, independent of natural growth. It may be congenital, compensatory, complementary or functional. See also stenosis.
hyperuricaemia excess of uric acid in the blood.
hyperventilation overbreathing. Increased respiratory rate; may occur during anxiety attacks, in salicylate poisoning or head injury, or passively as part of a technique of general anaesthesia in intensive care. Also associated with alkalosis and tetany.
hyperviscosity an extremely viscous or thick fluid.
hyperviscosity syndrome when the paraprotein level is raised and visual impairment, lethargy and coma therefore develop.
hypocalcaemia decreased calcium level in the blood. Causes include: disturbed kidney function, excess calcium excretion, deficiency of vitamin D, alkalosis and hypoparathyroidism. Leads to tingling in the hands and feet, and stridor and convulsions in children.
hypochondria unnecessary anxiety about one’s health.
hypochondriac associated with the regions of the upper abdomen beneath the lower ribs, associated with a person who is preoccupied with their health so that their state of mind itself becomes a disability.
hypochondriacal disorder an excessive preoccupation with the possibility of having serious health problems associated with refusal to accept professional reassurance that there is no physical illness underlying the symptoms. Symptoms are often of a bodily nature or concerned with physical appearance.
hypochondrium the upper lateral region (left and right) of the abdomen.
hypodermic below the skin; subcutaneous.
hypofractionation the practice of giving less than the conventional fractionations for a particular treatment, is used for treating tumours which have a higher capacity for repair such as melanomas.
hypogastrium that area of the anterior abdomen which lies immediately below the umbilical.
hypoglossal nerve the 12th pair of cranial nerves which innervate tongue movements.
hypoglycaemia a condition when the blood sugar is less than normal.
hypoglycaemic low blood sugar level.
hypoglycaemic coma occurs in diabetes, the patient looses consciousness if they have an overdose of insulin or have not eaten at the appropriate time.
hypokalemia lack of potassium in the blood.
hypomobility decrease in the normal range of joint movement.
hypomotility decreased movement, as of the gastrointestinal tract.
hypopharynx that portion of the pharynx lying below and behind the larynx, correctly called the laryngopharynx.
hypophysis cerebri see pituitary gland.
hypopituitarism pituitary gland insufficiency, especially of the anterior lobe. Absence of gonadotrophins leads to failure of ovulation, uterine atrophy and amenorrhoea in women and loss of libido, pubic and axillary hair in both sexes. Lack of growth hormone in children results in short stature. Lack of adrenocorticotrophin (ACTH) and thyrotrophin (TSH) may result in lack of energy, pallor, fine dry skin, cold intolerance and sometimes hypoglycaemia. Usually due to tumour of or involving pituitary gland or hypothalamus but in other cases cause is unknown. Occasionally due to postpartum infarction of the pituitary gland.
hypotension low blood pressure that is insufficient for adequate tissue perfusion and oxygenation; may be primary or secondary (e.g. reduced cardiac output, hypovolaemic shock, Addison’s disease) or postural.
hypothalamus literally, below the thalamus. It consists of an area of grey matter in the brain just above the pituitary gland. It has both endocrine and neural functions. The hypothalamus produces the hormones oxytocin and vasopressin (antidiuretic hormone); these are stored in the posterior pituitary prior to release. It is the major centre for the autonomic nervous system and controls physiological functions that include thirst and hunger, circadian rhythms and emotions such as anger.
hypothenar eminence the eminence on the ulnar side of the palm below the little finger.
hypothermia general lowering of body temperature, may occur when heat loss exceeds heat production. Occurs following shock or injury, often fatal if uncontrolled.
hypothesis a declaration that can be tested by statistical (inferential) tests. It is a prediction based on the relationship between the dependent and independent variables.
hypothetico-deductive method theories are examined and hypotheses for testing are derived in a deductive manner. The particular research study tests the hypotheses by data analysis that either supports or repudiates the original theory.
hypothyroidism conditions caused by low circulating levels of one or both thyroid hormones (thyroxine, triiodothyronine). Much more common in women than men and may be: (a) associated with goitre, such as autoimmune thyroiditis, lack of iodine or as a drug side-effect, e.g. with lithium; (b) due to spontaneous atrophy; or (c) after surgical treatment for hyperthyroidism. Some individuals have a subclinical form and in others it may be transient. It results in decreased metabolic rate and may be characterized by some of the following: fatigue, bradycardia, angina, hypertension, aches and pains, carpal tunnel syndrome, low temperature and cold intolerance, weight gain, constipation, hair and skin changes (dry coarse skin), puffy face, anaemia, hoarseness, slow speech, menorrhagia and depression. Treatment is with replacement thyroxine. congenital hypothyroidism can be detected (by routine blood testing) soon after birth and treated successfully with thyroxine. Untreated, it leads to impaired mental and physical development. It is recognized by the presence of coarse facies and protruding tongue. The term cretinism was previously used.
hypovolaemic shock shock caused by the loss of circulating blood volume as a result of dehydration, haemorrhage, vomiting, diarrhoea or severe burns. Used to be called medical shock.
hypoxaemia an insufficient oxygen content in the blood.
hypoxia diminished amount of oxygen in tissues.
hysterectomy surgical removal of the uterus. abdominal hysterectomy effected via a lower abdominal incision. subtotal hysterectomy removal of the uterine body, leaving the cervix in the vaginal vault. total hysterectomy complete removal of the uterine body and cervix. vaginal hysterectomy carried out through the vagina.
hysteresis is when a material is being magnetized the effect of magnetism lags behind the magnetizing force, the lag can be plotted to form a hysteresis loop.
hysterosalpingectomy excision of the uterus and uterine (fallopian) tubes.
hysterosalpingography the radiographic investigation of the uterus and uterine tubes following the introduction of contrast agent via a cannula inserted into the cervix. See also uterosalpingography.
hysterosalpingostomy anastomosis between a uterine (fallopian) tube and the uterus.
hysteroscopy the passage of a small-diameter telescope through the cervix to visualize the uterine cavity. Also used for treatments such as transcervical resection of endometrium.
