Encyclopedia of Health and Medicine

S
scrotum The saclike structure, a thin layer of
MUSCLE and SKIN, suspended from the base of a
man’s pelvis that contains the TESTICLES. A pair of
ligaments, the spermatic cords, extend from the
lower abdomen to support the scrotum. The spermatic
cords also serve as the conduits for the
BLOOD vessels and nerves that supply the testicles.
The abdominal and scrotal muscles contract or
relax to raise or lower the scrotum, maintaining
the appropriate temperature for spermatogenesis
(SPERM production). Sperm production, which is a
key function of the testicles, requires a temperature
of 96ºF to 96.5ºF, about 2 degrees lower than
body temperature. Pubic HAIR covers the outside of
the scrotum after PUBERTY.
See also HERNIA; SPERMATOCELE; VARICOCELE.
secondary sexual characteristics The physical
changes that distinguish the genders from each
other. Secondary sexual characteristics emerge
with PUBERTY and establish sexual and reproductive
maturity: males produce viable SPERM capable
of causing PREGNANCY, and females produce
ripened OVA (eggs) capable of fertilization that
results in pregnancy.
FEMALE SECONDARY SEXUAL CHARACTERISTICS
growth of pubic and axillary (underarm) HAIR
thickened and coarse or dark leg hair
enlarged breasts and broadened hips
MALE SECONDARY SEXUAL CHARACTERISTICS
growth of pubic, axillary, chest and facial hair
thickened, darkened, and coarse arm and leg hair
broadened shoulders and chest
increased MUSCLE mass and definition
deepened voice and prominent Adam’s apple in the THROAT
enlarged TESTICLES, enlarged and elongated PENIS
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See also CONCEPTION; CONTRACEPTION; FERTILITY;
MENSTRUAL CYCLE; MENSTRUATION; PREGNANCY.
semen The fluid of a man’s EJACULATION. In a fertile
man about 5 percent of the semen content is
SPERM; in a man who has had a VASECTOMY semen
does not contain sperm. The seminal vesicles and
the PROSTATE GLAND produce the milky fluid of
semen, which is primarily a water base that contains
proteins, sugars (notably fructose and some
GLUCOSE), lipids (fatty acids), electrolytes, and
PROSTAGLANDINS. The bulbourethral glands, also
called Cowper’s glands, add a gelatinous secretion
to the semen that thickens it. Semen may flow
back into the BLADDER rather than out of the PENIS
(RETROGRADE EJACULATION) in a man with a PROSTA-
TECTOMY (surgery to remove the prostate gland).
The electrolytes protect sperm on their journey
through the VAGINA and into the UTERUS. The sugars,
particularly fructose, and lipids provide nutrition
for the sperm. Vaginal secretions are highly
acidic and deadly to sperm. The thickness of
semen helps contain and insulate sperm as they
travel through the VAGINA, though the semen thins
by the time it reaches the UTERUS to release the
sperm. The electrolytes in semen make it highly
alkaline, helping neutralize the vaginal environment
to improve sperm survival. Prostaglandins
help suppress the IMMUNE RESPONSE, the natural
reaction of the woman’s IMMUNE SYSTEM to the
presence of the sperm. The semen also has the
ability to carry various pathogens such as viruses
and BACTERIA that can spread SEXUALLY TRANSMITTED
DISEASES (STDS).
Semen analysis is a laboratory examination of a
semen sample to measure the concentrations of its
ingredients and the number and characteristics of
the sperm. ALCOHOL consumption, cigarette smok-