Sperm are produced, stored, and delivered by the male
reproductive system. Here, you can see the parts of the male
reproductive system --
the testes, urethra, vas deferens, prostate,
seminal vesicle, and penis.
The testes contain coiled structures called seminiferous tubules,
which are the sites of sperm production. A woman’s ovaries need only
produce one egg per month, but a man’s seminiferous tubules
produce over12 billion sperm per month.
The structure on top of the seminiferous tubules is the epididymis.
The immature sperm migrate there to mature,
and then are stored there afterwards.
This trip usually takes about 20 days.
Before intercourse, the penis fills with blood and becomes erect.
Then, with sufficient stimulation,
an ejaculatory process begins.
Here you can see the mature sperm traveling from the epididymis
through the vas deferens, which 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. Here, a liquid secretion from the seminal
vesicles mixes with the sperm. Seminal fluid contains fructose sugar,
which the sperm use as fuel. It also has alkalines,
which help to counteract the naturally acidic environment of the
vagina and uterus so the sperm have a better chance for survival.
From there, 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, or 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.
Most of the sperm won't make it. Of the 300 million sperm ejaculated,
only about 200 or so will survive to reach the egg cell
and only one of those will succeed in fertilizing it.