I
ANATOMY
Anal stenosis is treated by
anal dilatation
(a procedure that expands or enlarges
the anus).
anal stricture
See
anal stenosis.
anal tag
A type of
skin tag.
analysis, chemical
Determination of the identity of a sub-
stance or of the individual chemical
constituents of a mixture. Analysis may
be
qualitative
(as
in
determining
whether or not a particular substance is
present), or it may be quantitative (that
is, measuring the amount or concen-
tration of one or more constituents).
(See also
assay
.)
analysis, psychological
See
psychoanalysis.
anaphylactic shock
A rare, life-threatening allergic reaction.
Anaphylactic shock is a Type I hypersen-
sitivity reaction (see
allergy)
that occurs
in people with extreme sensitivity to a
particular substance (an allergen), most
commonly
insect venom
or
certain
foods or drugs.
When the allergen enters the blood-
stream, massive amounts of
histamine
and other chemicals are released, caus-
ing sudden, severe lowering of blood
pressure and constriction of the air-
ways. Other symptoms of anaphylactic
shock may include abdominal pain,
diarrhoea, swelling of the tongue and
throat, and an itchy rash.
Anaphylactic shock requires emer-
gency medical treatment. An injection
of
adrenaline
(epinephrine) may be life-
saving.
If the person’s breathing
or
heartbeat has stopped,
cardiopulmonary
resuscitation
should be performed, and
antihistamine
drugs
and
corticosteroid
drugs
may also be given.
(See also
hyposensitization
.)
anastomosis
A natural or artificial communication
between two blood vessels or between
tubular cavities that may or may not
normally be joined.
Natural anastomoses usually occur
when small
arteries
are attached directly
to
veins
without passing through capil-
laries. Anastomoses occur in the skin
where they are used to help control
temperature regulation.
A surgical anastomosis is used to cre-
ate 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.)
anastrozole
An
anticancer drug
that is used to treat
advanced
breast cancer
in postmeno-
pausal women.
anatomical snuffbox
A depression on the back of the wrist
that is formed between the tendons of
the thumb when the thumb is stretched
outwards. The anatomical snuffbox is of
significance because tenderness in this
area is a feature of a fracture of the
scaphoid
bone.
anatomy
The structure of the body of any living
thing, and its scientific study Human
anatomy, together with
physiology
(the
study of the functioning of the body),
dates back to ancient Egyptian times
and forms the foundation of all medical
science.
The
dissection
of
human
corpses
has
provided
the
primary
source of information for anatomists.
Anatomy as a scientific study today is
subdivided into many branches. These
include comparative anatomy (the study
of the differences between human and
animal bodies), surgical anatomy (the
practical knowledge required by sur-
geons),
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
cytology
and
histology
(the micro-
scopic
study
of
cells
and
tissues
respectively).
Every anatomical structure is scientif-
ically
named
in
Latin,
but
today
anatomists prefer to use simpler terms,
HOW ANALGESICS WORK
When tissue is damaged (for example,
by injury, inflammation, or infection)
the body produces prostaglandins.
These substances combine with
receptors (specific sites on the surface
of cells in the brain and spinal cord).
As a result, a signal is passed along
a series of nerve cells to the brain,
where the signal is interpreted as
pain by brain cells. Analgesics
(except for paracetamol) work either
by preventing the production of
prostaglandins at the site of damage
or by blocking pain impulses in the
brain and spinal cord. Paracetamol
works by blocking prostaglandin
production in the brain, which
prevents pain impulses from
being transmitted in the brain.
Nerve ending
Nonopioid
drug
Prostaglandin
molecule
Damaged cell
Action of NSAIDs
Nonopioid drugs block the production
of prostaglandins (chemicals released in
response to tissue damage). Thisaction
prevents stimulation ofthe nerve endings,
so that no pain signal passes on to the brain.
As a result, these drugs provide pain relief.
Pain signal
to brain
Nerve ending
Prostaglandin
molecule
Damaged cell
Action of opioids
When tissue damage occurs, the body produces
prostaglandins, chemicals that trigger the
transmission ofpain signals(above). Normally,
the pain signal is transmitted between brain
cells, but opioid drugs (below) combine with
opiate receptors to prevent the signals from
being transmitted.
Brain cell
Receptor
Opioid drug
Pain signals in
brain blocked
A
45
previous page 44 BMA A Z Family Medical Encyclopedia   2004 read online next page 46 BMA A Z Family Medical Encyclopedia   2004 read online Home Toggle text on/off