ANCYLOSTOMIASIS
A
DESCRIPTIVE TERMS IN ANATOMY
The relative positions and
movements of body parts are
conventionally described with
reference to the “anatomical
position” (that is, an upright
posture with the eyes and palms
facing forwards). In this position,
the parts of the body can be
described in relation to various
geometrical planes.
In radiology, body imaging
pictures (such as CT scans and
MRI) are often taken in a series of
transverse planes through part of
the body.
Joint movements
Extension is straightening, and flexion is
bending; abduction is moving awayfrom,
adduction is moving towards, the midline
of the body. Other movements are forms of
rotation around an axis.
Sample coronal plane
Examples of
transverse, or
horizontal,
planes
Median, or
sagittal, plane
Planes through the body
The median plane divides the body into right
and left halves. Coronal planes are vertical
planes at right angles to the median plane;
the coronal plane most often referred to
divides the body into front and back halves.
Transverse planes are horizontal slices
through the body.
where they exist, as alternatives. For
example, the main blood vessel in the
femur (thigh) is usually referred to as
the femoral artery rather than the arte-
ria femoralis. For further information
on the descriptive terms used in ana-
tomy, see the illustrated box.
ancylostomiasis
Infestation of the small intestine by the
A
ncylosTOMA
hookworm species.
(See
also
hookworm infestation.)
androblastoma
See
arrhenoblastoma.
androgen drugs
Natural or synthetic
androgen hormones
(male sex hormones) that are used as
drugs, of which one of the most impor-
tant is
testosterone.
Androgen drugs are
used in the treatment of male
hypo-
gonadism
(underactivity of the testes)
to stimulate the development of male
sexual characteristics.
Androgen
drugs
are
occasionally
used to treat certain types of
breast
cancer.They
have also been widely used
by athletes and bodybuilders wishing to
increase their muscle bulk and strength,
which can be dangerous to health (see
steroids, anabolic).
Possible side
effects include
fluid
retention, weight gain, increased blood
cholesterol, and, rarely, liver damage.
When taken by women, the drugs can
lead to the development of male charac-
teristics, such as facial hair.
androgen hormones
A group of hormones (the male sex
hormones)
that
stimulate
virilization
(the development of male secondary
sexual characteristics such as growth of
facial hair, deepening of the voice, and
increased muscle bulk).
FORMATION
Androgens are produced by specialized
cells in the
testes
in males and the adre-
nal glands in both sexes. The ovaries
secrete very small quantities of androgens
until the menopause. The most active
androgen is
testosterone
(produced in
the testes). Androgen production by the
testes is controlled by certain pituitary
hormones called
gonadotrophins.Adrenal
androgens
are
controlled
by
ACTH
,
another pituitary hormone.
EFFECTS
Androgens stimulate the appearance, at
puberty,
of male secondary sexual char-
acteristics such as deepening of the
voice and the growth of facial hair. They
have an anabolic effect (they raise the
rate of protein synthesis and lower the
rate at which it is broken down), which
increases muscle bulk and accelerates
growth. At the end of puberty, andro-
gens cause the long bones to stop
growing. They also stimulate the secre-
tion of sebum, which, if excessive,
causes
acne.
In early adult life, andro-
gens promote male-pattern baldness.
DEFICIENCY
Androgen deficiency may occur if the
testes are diseased or the pituitary gland
fails to secrete gonadotrophins. Typical
effects
include
high-pitched
voice,
decreased body and facial hair, under-
developed
genitalia,
reduced
sexual
drive, and poor muscle development.
EXCESS
Overproduction of androgens may be
the result of adrenal disorders such as
adrenal
tumours,
congenital
adrenal
hyperplasia (see
adrenal hyperplasia, con-
genital
), testicular tumours (see
testis
,
cancer of
), or, rarely, androgen-secreting
ovarian tumours (see
ovary, cancer of).
In men, excess androgens accentuate
male physical characteristics; in boys,
they cause premature sexual develop-
ment.
In women,
excess
androgens
cause virilization,
features
of which
include increased body hair, deepening
of the voice, enlarged
clitoris,
and
amen-
orrhoea
(the absence of menstruation).
anencephaly
Absence of the brain and cranial vault
(top of the skull) at birth. Most infants
with anencephaly are stillborn or survive
for only a few hours. Anencephaly is
detectable early in pregnancy by meas-
urement of the maternal
alpha-fetoprotein,
46
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