The testes, as stated earlier, are the primary male
reproductive organs. They produce sperm cells
(spermatozoa) and male hormones, both necessary for
The testes are oval glands suspended inside a sac
(the scrotum) by a spermatic cord. The spermatic
cords are formed by the vas deferens, arteries, veins,
lymphatics, and nerves, all bound together by
Each testis is encapsulated by a tough, white,
fibrous tissue called the tunica albuginea. The interior
of the testis is divided into 250 lobules (small lobes).
Each lobule contains 1 to 4 highly coiled, convoluted
tubules called seminiferous tubules. These tubules
unite to form a complex network of channels called the
rete testis. The rete testis give rise to several ducts that
join a tube called the epididymis (fig. 1-60).
The testes perform two functions: to produce
sperm cells and to secrete male sex hormones. The
process by which sperm cells are produced is called
spermatogenesis. Spermatogenesis occurs in the
seminiferous tubules of the testes. Once the sperm
cells are formed, they collect in the lumen of each
seminiferous tubule. When the sperm cells are ready,
they pass through the rete testis to the epididymis,
where they remain for a time to mature. The production
of sperm cells occurs continually throughout the
reproductive life of a male.
The male hormone testosterone is produced in the
testes. This hormone is initially responsible for the
formation of the male reproductive organs. During
puberty, testosterone stimulates the enlargement of the
testes and various other accessory reproductive
organs. It also causes the development of the male
secondary sexual characteristics. Refer to the section
titled The Endocrine System for more detailed
discussion on male secondary sexual characteristics.
Other actions of testosterone include increasing
the production of red blood cells. As a result, the
average number of red blood cells in blood is usually
greater in males than in females.
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.
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.
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.
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.
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.