I
ACTH
The common abbreviation for adreno-
corticotrophic
hormone
(also
called
corticotrophin). ACTH is produced by
the anterior part of the
pituitary gland
(at
the base of the brain) and stimulates the
adrenal
cortex
(the
outer
layer
of
the
adrenal glands,
situated on the top of
the kidneys) to release various
cortico-
steroid hormones.
ACTH is also necessary
for the growth and maintenance of the
cells of the adrenal cortex.
ACTIONS
The most important function of ACTH
is to stimulate the adrenal cortex to
increase its production of
hydrocortisone
(cortisol). ACTH also causes the adrenal
cortex to release
aldosterone
and
andro-
gen hormones.
The production of ACTH is controlled
by a feedback mechanism that involves
both the
hypothalamus
(an area in the
centre of the brain) and the level of
hydrocortisone
in
the
blood. When
ACTH levels are high, the production of
hydrocortisone increases, which in turn
suppresses the release of ACTH from the
pituitary gland. If ACTH levels are low,
hydrocortisone production falls and the
hypothalamus releases factors that stim-
ulate the pituitary gland to increase
production of ACTH.
ACTH levels increase in response to
stress, emotion, injury, burns, infection,
surgery, and decreased blood pressure.
Cancerous tumours, particularly those
of the lung, can sometimes produce a
chemical that is similar to ACTH and
which causes symptoms.
DISORDERS OF ACTH PRODUCTION
A tumour of the pituitary gland can
cause excessive production of ACTH,
which, in turn, leads to overproduction
of hydrocortisone by the adrenal cor-
tex, resulting in
Cushing’s syndrome
(a
hormonal disorder). Insufficient ACTH
production results in decreased pro-
duction
of
hydrocortisone,
causing
hypotension
(low blood pressure).
MEDICAL USES
Synthetic ACTH was once given in the
treatment of
arthritis
or to treat
allergy
,
but it is now rarely used.
actin
A
protein
component of
muscle
fibres
that, together with myosin
(another
protein), provides the mechanism for
muscles to contract. The microscopic
filaments of actin and myosin slide in
between each other to make the muscle
fibres shorter.
ADAM’S APPLE
acting out
Impulsive actions that may reflect an
individual’s unconscious wishes. The
term is most often used by psycho-
therapists to describe behaviour during
analysis when the patient “acts out”,
rather than reports, his or her fantasies,
wishes, or beliefs. Acting out can also
occur
as
a
reaction
to
frustrations
encountered in everyday life, often tak-
ing the form of antisocial, aggressive
behaviour that may be directed against
oneself or others.
actinic
Relating to changes caused by the ultra-
violet rays in sunlight, as in actinic
dermatitis
(inflammation of the skin) and
actinic
keratosis
(roughness and thick-
ening of the skin). Both are caused by
overexposure to solar radiation.
actinomycosis
An
infection
caused by ACTINOMYCES
ISRAELII or related actinomycete bacteria.
These
bacteria
resemble
fungi
and
cause diseases of the mouth, jaw, chest,
and pelvis.
TYPES AND CAUSES
The most common form of actinomy-
cosis affects the jaw area. A painful
swelling appears and pus and char-
acteristic
yellow
granules
discharge
through small openings that develop in
the skin. Poor oral hygiene may con-
tribute to this form of the infection.
Another form of actinomycosis affects
the pelvis in women, causing lower
abdominal pain and bleeding between
menstrual periods. This form was asso-
ciated mainly with a type of
IUD,
no
longer in use, that did not contain cop-
per. Rarely, forms of the disorder affect
the appendix or lung.
Actinomycosis is usually treated suc-
cessfully with
antibiotic drugs.
acuity, visual
See
visual acuity.
acupressure
A derivative of
acupuncture
in which
pressure is applied instead of needles.
acupuncture
A branch of
Chinese medicine
in which
needles are inserted into a patient’s skin
as therapy for various disorders, to
relieve pain or to induce
anaesthesia.
Traditional Chinese medicine main-
tains that the
chi
(life-force)
flows
through
the
body
along
channels
known as meridians. A blockage in one
or more of these meridians is thought
to cause ill health. Acupuncturists aim
to restore health by inserting needles at
appropriate sites, known as acupuncture
points, along the affected meridians.
HOW IT WORKS AND WHY IT IS DONE
Research
suggests
that
acupuncture
provokes the release within the central
nervous
system
of
endorphins
(sub-
stances resembling morphine), which
act as natural analgesics (painkillers).
The disorder that is being treated and
degree of anaesthesia required deter-
mine the needle temperature, place of
insertion, whether the needles are stim-
ulated by rotation or electric current,
and the length of time the needles
remain in position.
Acupuncture
may be
used as
an
anaesthetic for surgical procedures as
well as to provide pain relief following
operations and for chronic conditions.
acupuncture is also claimed to help in
the treatment of addiction, depression,
and anxiety.
SIDE EFFECTS
After treatment with acupuncture, some
people experience temporarily exacer-
bated symptoms. Other people may feel
lightheaded, drowsy, or exhilarated for
a short while.
It is important that acupuncture is
performed by a fully qualified acupunc-
turist because the use of inadequately
sterilized needles could result in the
transmission of a variety of infections,
including
hepatitis B
and
HIV.
acute
A term often used to describe a disorder
or symptom that develops suddenly.
Acute conditions may or may not be
severe, and they are usually of short
duration. (See also
chronic.)
acute heart failure
See
heart failure, acute.
acyanotic
A diagnostic term meaning without
cya-
nosis,
a bluish coloration of the skin
that is seen when blood
oxygen
levels are
abnormally low. The term is commonly
used in relation to the classification of
congenital (present from birth) heart
disease (see
heart disease, congenital).
Adam’s apple
The projection at the
front
of the
neck, just beneath the skin, that is
formed by a prominence on the thyroid
A
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