Bma Illustrated Medical Dictionary

history-takingThe process by which a

doctor learns from patients the symp-

toms of their illnesses and any previous

disorders. (See also diagnosis.)

HIVThe abbreviation for human immuno-

deficiency virus. HIV is a retrovirus (see

virus) and is the cause of AIDS. There

are 2 closely related viruses: HIV-1, which

is the most common cause of AIDS

throughout the world; and HIV-2, which

is largely confined to West Africa.

HIV gains access to the body through

contaminated blood transfusions, non-

sterile needles, or sexual intercourse. A

fetus may be infected via the placenta.

HIV has an affinity for the T-lymphocytes,

in which the virus multiplies and, in

some cases, destroys function. People

with HIV infection should have regular

monitoring in order to determine when

specific treatments, such as antiretroviral

drugs, are necessary.

hivesAn alternative name for urticaria.

HLAThe abbreviation for human leuko-

cyte antigen.

HLA typesSee histocompatibility antigens.

hoarsenessA rough, husky, or croaking

voice. Short-lived hoarseness is often

due to overuse of the voice, which

strains the muscles in the larynx. It is

also commonly caused by inflammation

of the vocal cords in acute laryngitis.

Persistent hoarseness may be due to

chronic irritation of the larynx, which can

be caused by smoking, excessive con-

sumption of alcohol, chronic bronchitis,

histamine 2 -receptor antagonistsSee

H 2 -receptor antagonists.

histiocytosis XA rare childhood dis-

ease in which there is an overgrowth of

a type of tissue cell called a histiocyte.

The cause is unknown, but histiocytosis X

probably results from a disturbance of

the immune system. In the mildest form,

rapid cell growth occurs in 1 bone only,

usually the skull, a clavicle, a rib, or a

vertebra, causing swelling and pain. In

the most severe, and least common,

form, there is a rash and enlargement of

the liver, spleen, and lymph nodes.

histocompatibility antigensA group

of proteins that have a role in the

immune system. Certain types of histo-

compatibility antigens are essential for

the immunological function of killer T

cells (see lymphocytes). The antigensact

as a guide for killer T cells to recognize

and kill abnormal or foreign cells.

The main group of histocompatibility

antigens is the human leukocyte antigen

(HLA) system, which consists of several

series of antigens. A person’s tissue type

(the particular set of HLAs in the body

tissues) is unique, except for identical

twins, who have the same set.

HLA analysis has some useful appli-

cations. Comparison of HLA types may

show that 2 people are related, and it has

been used in paternity testing. The HLA

system is also used in tissue-typingto

help match recipient and donor tissues

before transplant surgery. Certain HLA

types occur more frequently in people

with particular diseases, such as multiple

sclerosis, coeliac disease, and ankylosing

spondylitis. HLA testing can help to con-

firm the presence of such diseases and

identify people at risk of developing them.

histologyThe study of tissues, includ-

ing their cellular structure and function.

The main application of histology in

medicine is in the diagnosis of disease.

histopathologyA branch of histology

concerned with the effects of disease on

the microscopic structure of tissues.

histoplasmosisAn infection caused by

inhaling the spores of the fungus HISTO-

PLASMA CAPSULATUM, which is found in

soil contaminated with bird or bat

droppings. It occurs in parts of the

Americas, the Far East, and Africa.

HOARSENESS

H

HIV

Cross-sectioned

virus

Genetic

material

Outer shell

of virus

HUMAN IMMUNODEFICIENCY VIRUSES

HISTAMINE 2 -RECEPTOR ANTAGONISTS