of a weak opioid analgesic, such as
codeine, with a nonopioid analgesic
relieve more severe pain. Potent opioids
such as morphineare used only when
other preparations would be ineffective
because they can produce tolerance
and drug dependence.
Adverse effects are uncommon with
paracetamol. Aspirin and NSAIDs may
irritate the stomach lining and cause
nausea, abdominal pain, and, rarely, a
peptic ulcer. Nausea, drowsiness, con-
stipation, and breathing difficulties may
occur with opioid analgesics.
anal stenosisA tightness of the anus,
sometimes referred to as anal stricture.
Anal stenosis prevents the normal pas-
sage of faeces, causing constipation and
pain during defaecation. The condition
may be present from birth, or may be
caused by a number of conditions in
which scarring has occurred, such as
anal fissure, colitis, or cancer of the anus.
Anal stenosis sometimes occurs after
surgery on the anus (for example, to
treat haemorrhoids). The condition is
treated by anal dilatation.
anal strictureSee anal stenosis.
anal tagA type of skin tag.
analysis, chemicalDetermination of
the identity of a substance or of the
individual chemical constituents of a
mixture. Analysis may be qualitative, as
in determining whether a particular
substance is present, or it may be quan-
titative, that is, measuring the amount
or concentration of one or more consti-
tuents. (See also assay.)
analysis, psychologicalSee psycho-
analysis.
anaphylactic shockA rare, life-threat-
ening allergic reaction that occurs in
people with an extreme sensitivity to a
particular substance (allergen), often in-
sect venom, a food item, or a drug (see
allergy). When the allergen enters the
bloodstream, massive amounts of hista-
mineand other chemicals are released,
causing sudden, severe lowering of
blood pressure and constriction of the
airways. Other symptoms may include
abdominal pain, diarrhoea, swelling of
the tongue and throat, and itchy rash.
Anaphylactic shock requires emerg-
ency medical treatment. An injection of
adrenalinemay be life-saving. Antihis-
tamine drugsand corticosteroid drugs
may also be given.
anastomosisA natural or artificial
communication between 2 blood ves-
sels or tubular cavitiesthat may or may
not normally be joined. Natural anasto-
mosesusually occur when small arteries
are attached directly to veinswithout
passing through capillaries. They occur
in the skin and are used to help control
temperature regulation. Surgical anas-
tomoses are used to create a bypass
around a blockage in an artery or in the
intestine. They are also used to rejoin
cut ends of the bowel or blood vessels.
(See also bypass surgery.)
anatomyThe structure of the body of
any living thing, and its scientific study.
Human anatomy, together with physiol-
ogy(the study of the functioning of the
body), forms the foundation of medical
science. Anatomy is subdivided into
many branches. These include compara-
tive anatomy (the study of the differences
between human and animal bodies),
surgical anatomy (the practical know-
ledge required by surgeons), embryology
(the study of structural changes that
occur during the development of the
embryo and fetus), systematic anatomy
(the study of the structure of particular
body systems), and cytologyand histol-
ogy(the microscopic study of cells and
tissues respectively).
ancylostomiasisSee hookworm infes-
tation.
androgen drugsNatural or synthetic
androgen hormonesused as drugs; one
of the most important is testosterone.
These drugs are used in the treatment
of male hypogonadism(underactivity of
the testes) to stimulate the development
of sexual characteristics.
Androgen drugs are occasionally used
to treat certain types of breast cancer.
They have been widely used by sports-
men wishing to increase muscle bulk
and strength, a practice that is danger-
ous to health (see steroids,anabolic).
Adverse effects include fluid retention,
weight gain, increased blood cholesterol,
and, rarely, liver damage. When taken by
women, the drugs can cause male char-
acteristics, such as facial hair, to develop.ANAL STENOSIS ANDROGEN DRUGS
A