with radiotherapy to shrink the tumour
is also effective.
acrocyanosisA circulatory disorder in
which the hands and feet turn blue, may
become cold, and sweat excessively.
Acrocyanosis is caused by spasm of the
small blood vessels and is often aggra-
vated by cold weather. It is related to
Raynaud’s disease.
acrodermatitis enteropathicaA rare
inherited disorder in which areas of the
skin (most commonly the fingers, toes,
scalp, and the areas around the anus
and mouth) are reddened, ulcerated, and
covered with pustules. Acrodermatitis
enteropathica is due to an inability to
absorb enough zinc from food. Zinc
supplements usually help.
acromegalyA rare disease characterized
by abnormal enlargement of the skull,
jaw, hands, feet, and also of the internal
organs. It is caused by excessive secre-
tion of growth hormone from the
anterior pituitary gland at the base of
the brain and is the result of a pituitary
tumour. A tumour that develops before
puberty results in gigantism. Acromeg-
aly is diagnosed by measuring blood
levels of growth hormone, followed by
CT scanningor MRI.
acromioclavicular jointThe joint that
lies between the outer end of the cla-
vicle (collarbone) and the acromion
(the bony prominence at the top of the
scapula(shoulderblade).acromionA bony prominence at the
top of the scapula(shoulderblade). The
acromion articulates with the end of
the clavicle(collarbone) to form the
acromioclavicular joint.acroparaesthesiaA medical term used
to describe tingling in the fingers or
toes (see pins-and-needles).
ACTHThe common abbreviation for
adrenocorticotrophic hormone (also
called corticotrophin). ACTH is produced
by the anterior pituitary glandand stim-
ulates the adrenal cortex (outer layer of
the adrenal glands) to release various
corticosteroid hormones,most impor-
tantlyhydrocortisone(cortisol) but also
aldosteroneand androgen hormones.
ACTH production is controlled by a
feedback mechanism involving both the
hypothalamusand the level of hydro-
cortisone in the blood. ACTH levels
increase in response to stress, emotion,
injury, infection, burns, surgery, and
decreased blood pressure.
A tumour of the pituitary gland can
cause excessive ACTH production which
leads to overproduction of hydrocorti-
sone by the adrenal cortex, resulting in
Cushing’s syndrome. Insufficient ACTH
production results in decreased produc-
tion of hydrocortisone, causing low
blood pressure. Synthetic ACTH is occa-
sionally given by injection to treat
arthritisor allergy.
actinA proteininvolved in musclecon-
traction, in which microscopic filaments
of actin and another protein, myosin,
slide in between each other.
acting outImpulsive actions that may
reflect unconscious wishes. The term is
most often used by psychotherapists
to describe behaviour during analysis
when the patient “acts out” rather than
reports fantasies, wishes, or beliefs.
Acting out can also occur as a reaction
to frustrations encountered in everyday
life, often taking the form of antisocial,
aggressive behaviour.
actinicPertaining to changes caused by
the ultraviolet rays in sunlight, as in
actinic dermatitis(inflammation of the
skin) and actinic keratosis(roughness
and thickening of the skin).
actinomycosisAn infection caused by
ACTINOMYCES ISRAELII or related actino-
mycete bacteria. The most common
form of actinomycosis affects the jaw
area. A painful swelling appears and
pus discharges through small openings
that develop in the skin. Another formACROCYANOSIS ACTINOMYCOSISA
Acromioclavicular
jointAcromionACROMIOCLAVICULAR JOINTClavicleHumerusScapula