Webster's New World Medical Dictionary

selective mutism
An inability to speak in certain
situations. See also 
apraxia; autism; elective
mutism; mutism; social phobia.
selective serotonin reuptake inhibitor
See
SSRI.
selenium
An essential mineral that is a compo-
nent of an antioxidant enzyme, glutathione reduc-
tase, that is key in tissue respiration. Food sources
of selenium include seafoods; some meats, such as
kidney and liver; and some grains and seeds. Too
much selenium may cause reversible balding and
changes in the nails, give a garlic odor to the breath,
and cause intestinal distress, weakness, and slowed
mental functioning. Deficiency of selenium causes
Keshan disease.
selenium deficiency
See 
deficiency, selenium.
sella turcica
A depression in the base of the
skull where the pituitary gland is situated. It was
called the sella turcica (the Turkish saddle)
because of its resemblance to a saddle used by the
Turks which had supports in the front and back.
semen
The fluid that is released through the
penis during orgasm. Semen is made up of fluid and
sperm. The fluid comes from the prostate, seminal
vesicles, and other sex glands. The sperm are man-
ufactured in the testicles. The seminal fluid helps
transport the sperm during orgasm. Seminal fluid
contains sugar as an energy source for sperm.
semen analysis
A laboratory test that measures
the amount of semen a man produces and deter-
mines the number and quality of sperm in the
semen sample. A semen analysis is usually one of
the first tests done to help determine whether a man
has a problem fathering a child (infertility).
seminal vesicle
One of two structures that are
about 5 cm long and are located behind the bladder
and above the prostate gland. The seminal vesicles
contribute fluid to the ejaculate.