Sperm are produced, stored, and
delivered by the male reproductive system. The
male reproductive system includes the testes,
urethra, vas deferens, prostate gland, seminal
vesicle, and penis. The testes contain coiled
structures called seminiferous tubules, which
are the sites of sperm production. They produce
over 12 billion sperm per month. The epididymis
lies on top of the seminiferous tubules. Immature
sperm migrate from the seminiferous tubules to
the epididymis to mature and be stored. The migration
process usually takes about 20 days.
Before intercourse,
the penis fills with blood and becomes erect.
With sufficient stimulation, the ejaculatory
process begins. The mature sperm travel from
the epididymis through the vas deferens. The
vas deferens is a narrow, muscular tube about
18 inches long. Its smooth muscle contractions
propel the sperm forward. They arrive first at
the ampulla, the widest part of the vas deferens,
and then pass into the ejaculatory ducts.
In
the ejaculatory ducts, a liquid secretion from
the seminal vesicles mixes with the sperm. Seminal
fluid contains fructose sugar, which the sperm
use as fuel as well as alkalines, which help
to counteract the naturally acidic environment
of the vagina and uterus providing the sperm
a better chance for survival. The liquid mixture
is propelled forward through the ejaculatory
ducts toward the urethra, passing first through
the prostate gland, where milky prostatic fluid
is added, forming the substance we call semen.
The prostatic fluid helps the sperm swim faster,
which is important for getting to the egg cell.
Finally,
about a teaspoon of semen is ejected out (ejaculated)
through the far end of the urethra at the end
of the penis. From the time the sperm leave the
man's body, they have between
12 and 48 hours to find and fertilize the egg
cell, assuming an egg is available. Of the 300
million sperm ejaculated, only about 200 or so
will survive to reach the egg cell and only one
will succeed in fertilizing it.
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