Bma Illustrated Medical Dictionary

Disturbances of the body’s acid–base
balance result in either acidosis(exces-
sive blood acidity) or alkalosis(excessive
blood alkalinity).
acidosisA disturbance of the body’s
acid–base balance in which there is an
accumulation of acid or loss of alkali
(base). There are 2 types of acidosis:
metabolic and respiratory.
One form of metabolic acidosis is
ketoacidosis, which occurs in uncon-
trolled diabetes mellitusand starvation.
Metabolicacidosismay also be caused
by loss of bicarbonate (an alkali) as a
result of severe diarrhoea. In kidney fail-
ure, thereis insufficient excretion of
acid in the urine.
Respiratory acidosis occurs if breathing
fails to remove enough carbondioxide
from the lungs. The excess carbon di-
oxide remains in the bloodstream,
where it dissolves to form carbonic acid.
Impaired breathing leading to respira-
tory acidosis may be due to chronic
obstructive pulmonary disease (see pul-
monary disease, chronic obstructive),
bronchial asthma, or airway obstruction.
acid refluxRegurgitation of acidic fluid
from the stomach into the oesophagus
due to inefficiency of the muscular valve
at the lower end of the oesophagus.
Also known as gastro-oesophageal
reflux disease (GORD), acid reflux may
inflame the oesophagus, resulting in
heartburndue to oesophagitis. It may
occur in pregnancy and often affects
overweight people.
acneA chronic skin disorder caused by
inflammation of the hair follicles and
sebaceous glands in the skin. The most
common type is acne vulgaris, which
almost always develops during puberty.
Acne spots are caused by the obstruc-
tion of hair follicles by sebum (the oily
substance secreted by the sebaceous
glands). Bacteria multiply in the follicle,
causing inflammation. The change in
sebum secretion at puberty seems to be
linked with increased levels of androgen
hormones (male sex hormones).
Acne may be brought on or aggravated
by drugs such as corticosteroids and
androgens. Exposure to certain chemi-
cals and oils in the workplace can also
cause a type of acne.

Acne develops in areas of skin with a

high concentration of sebaceous glands,

mainly the face, centre of the chest,

upper back, shoulders, and around the

neck. Milia (whiteheads), comedones

(blackheads), nod-

ules (firm swel-

lings beneath the

skin), and cysts

(larger, fluid-filled

swellings) are the

most commonly

occurring spots.

Some, particularly

cysts, leave scars

after they heal.

There is no inst-

ant cure for acne,

but washing the

affected areas at

least twice daily

may help to keep

it under control.

Topical drug treat-

ments, such as benzoyl peroxide or

retinoic acid, unblock the pores and

promote healing. Ultraviolet light can

be beneficial. If topical treatment has

failed, oral drug treatment with anti-

biotics,hormones, or isotretinoinmay be

given. Acne improves slowly over time,

often clearing up by the end of the

teenage years.

acoustic nerveThe part of the vestibu-

locochlear nerve(the 8th cranial nerve)

that is concerned with hearing. It is also

known as the auditory nerve.

acoustic neuromaA rare, noncancer-

ous tumour arising from supporting

cells that surround the 8th cranial nerve

(see acoustic nerve), usuallywithin the

internal auditory meatus (the canal in

the skull through which the nerve pass-

es from the inner ear to the brain).

Usually, the cause of an acoustic neuro-

ma is unknown. However, tumours that

affect the nerves on both sides of the

head simultaneously may be part of a

condition known as neurofibromatosis.

Acoustic neuroma can cause deafness,

tinnitus, loss of balance, and pain in the

face and the affected ear.

Diagnosis is made by hearing testsfol-

lowed by X-rays, CT scanning, or MRI.

Surgery may be needed, but treatment

ACIDOSIS ACOUSTIC NEUROMA

A

Pus

Plug

ACNE SPOT

ACNE

Hair

Sebaceous

gland

Inflamed skin