SPERMATIC CORD
SPINA BIFIDA
Sperm are produced within the seminif-
erous tubules of the
testes
and mature in
the
epididymis.
Production and develop-
ment of sperm cells is dependent on
testosterone
and on
gonadotrophin hor-
mones
secreted by the
pituitary gland.
Sperm production starts at
puberty
.
spermatic cord The structure in males
that runs from the abdomen to the
scrotum and contains the
vas deferens.
(See also
reproductive system, male
.)
spermatocele A harmless cyst of the
epididymis
containing fluid and sperm.
spermatozoa See
sperm.
spermicides Contraceptive preparations
that kill
sperm.
They are usually recom-
mended for use with
SPF
Sun protec-
tion
factor,
the
degree of protec-
tion a
sunscreen
provides against
sunburn. It is a
measure of the
amount of UVB
radiation a sun-
screen
absorbs:
the
higher
the
number, the more
the protection,
sphenoid
bone
The
bat-shaped
bone in the cen-
tre of the base of
the
cranium.
spherocytosis,
hereditary An inherited disorder in
which there are a large number of
unusually small, round red blood cells
(spherocytes) in the circulation. These
abnormal red cells are readily broken up
when blood passes through the
spleen.
At times, the rate of red cell destruction
exceeds the rate at which new cells can
be made in the bone marrow, leading to
symptoms of
anaemia
. Other symptoms
include
jaundice
and enlargement of the
spleen. Occasionally, crises occur (usu-
ally triggered by infection) in which all
symptoms worsen.
Gallstones
are a fre-
quent complication.
Splenectomy
usually
leads to permanent improvement.
sphincter A ring of muscle around a
natural opening or passage that acts as
a valve, regulating inflow or outflow.
sphincter, artificial A surgically creat-
ed valve or other device used to treat or
prevent urinary or faecal
incontinence.
sphincterotomy A surgical procedure
that involves cutting the muscle that
closes a body opening or that constricts
the opening between body passages.
sphygmomanometer
An
instrument
used for measuring
blood pressure
. A
cuff attached to the device is wrapped
around the person's arm and inflated
until it compresses the main artery in
the arm. The cuff is deflated while the
doctor listens to the blood flow through
a stethoscope. The sphygmomanometer
records the pressure on a mercury-filled
spider bites Nearly all spiders produce
venom, which they use to kill their prey.
However, only a few species, such as the
black widow in North America, are harm-
ful to humans.
Antivenoms
are available
for many dangerous spider bites,
spider naevus A red, raised pinhead-
sized dot, from
which
small blood
vessels radiate, due to a dilated minor
artery and its connecting capillaries.
Small numbers of spider naevi are com-
mon in children and pregnant women,
but in larger numbers, they may indicate
liver disease. (See also
telangiectasia.)
spina bifida A
congenital
defect that is a
type of
neural tube defect
in which part
of
1
or more
vertebrae
fails to develop
completely. As a result, a portion of the
spinal cord
is left exposed.
a barrier device.
glass column or a digital display.
SPHYGMOMANOMETER
Sphygmomanometer
519
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