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INTERNAL ACCESSORY ORGANS
The internal accessory organs of the male
reproductive system include the epididymis, vas
deferens, ejaculatory ducts, seminal
vesicle, urethra, prostate gland,
bulbourethral glands, and semen (fig.
1-60).
Epididymis
Each epididymis is a tightly coiled, thread-like
tube that is approximately 6 meters long. This tube is
connected to the ducts within the testis.
The epididymis covers the top of the
testis, runs down the testis' posterior
surface, and then courses upward to
form the vas deferens.
The epididymis secretes the hormone glycogen,
which helps sustain the lives of stored sperm cells and
promotes their maturation. When immature
sperm cells enter the epididymis, they
are not mobile. However, as the sperm
cells travel through the epididymis,
they mature and become mobile. Once the
sperm cells are mature, they leave the epididymis and
enter the vas deferens.
Vas Deferens
The vas deferens is a small tube that connects the
epididymis and ejaculatory duct. It ascends
as part of the spermatic cord through
the inguinal canal of the lower
abdominal wall into the pelvic cavity, and
transmits the sperm to the ejaculatory ducts.
Ejaculatory Ducts
The vas deferens and the seminal vesicles
converge, just before the entrance of the prostate
gland, to form the ejaculatory ducts (fig.
1-60). The ejaculatory ducts open into
the prostatic urethra. Its function is
to convey sperm cells to the urethra.
Seminal Vesicles
The seminal vesicles are two pouches that are
attached to the vas deferens near the base of the urinary
bladder. The lining of the inner walls of
the seminal vesicles secrete a slightly
alkaline fluid. This fluid is thought
to help regulate the pH of the tubular contents
as sperm cells are conveyed to the outside. The
secretion produced by the seminal vesicles
also contains a variety of nutrients,
such as fructose (simple sugar), that
provides the sperm cells an energy source.
At the time of ejaculation, the contents of the
seminal vesicles are emptied into the ejaculatory ducts.
This action greatly increases the volume of
fluid that is discharged by the vas
deferens.
Urethra
The urethra is an important organ of both the
urinary and reproductive systems. The role of the
urethra, in the reproductive system, is to
transport sperm through the penis to
outside the body. See "The Urinary
System" section for information on the
structure of the urethra.
Prostate Gland
The prostate gland, made of smooth muscle and
glandular tissue, surrounds the first part of the urethra.
It resembles a chestnut in shape and size,
and secretes an alkaline fluid to keep
the sperm mobile, protecting it from
the acid secretions of the female vagina. This
substance is discharged into the urethra as part of the
ejaculate, or semen, during the sexual act.
Bulbourethral Glands
Bulbourethral glands, also known as Cowper's
glands, are two pea-sized bodies located below the
prostate gland and lateral to the membranous
urethra. These glands are enclosed by
fibers of the external urethral
sphincter. They release a mucous-like fluid in
response to sexual stimulation and provide lubrication
to the end of the penis in preparation for
sexual intercourse.
Semen
Semen is composed of sperm and secretions from
the seminal vesicles, prostate, and bulbourethral
glands. It is discharged as the ejaculate
during sexual intercourse. There are
millions of sperm cells in the semen of
each ejaculation, but only one is needed to
fertilize the ovum. It is generally considered that
fertilization of the ovum occurs while it is
still in the fallopian tubes.
Therefore, it is apparent that sperm
cells can move actively in the seminal fluid deposited
in the vagina and through the layers of the
secretion lining the uterus and
fallopian tubes.
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