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U N I T 1 1
Genitourinary and Reproductive Function
The process of spermatogenesis begins with the sper-
matogonial phase, during which the spermatogonia
undergo mitotic division to form more spermatogonia
as well as primary spermatocytes (Fig. 39-3B). During
the next phase of spermatogenesis, the primary sper-
matocyte undergoes meiotic division during which its 46
chromosomes (23 pairs) are divided so that 23 chromo-
somes go to one secondary spermatocyte and the other
23 to another secondary spermatocyte. During the final
stage of spermatogenesis, the secondary spermatocytes
divide to form spermatids, which develop into mature
spermatozoa or sperm cells.
After their development in the seminiferous tubules,
the spermatozoa move into a highly convoluted network
of ducts called the
rete testis
(see Fig. 39-2). The spermato-
zoa are then transported through the efferent ductules and
into a single duct called the
epididymis
, which is the final
site for sperm maturation.
1,2
The epididymis also serves
as a reservoir for sperm. Sperm can be stored in the epi-
didymis for several months. If held longer they are eventu-
ally phagocytized by the epithelial cells of the epididymis.
When the male is sexually stimulated and ejaculates, the
smooth muscle in the wall of the epididymis contracts vig-
orously, moving sperm into the next segment of the ductal
system, the
ductus deferens
, also called the
vas deferens
(Fig. 39-4). The ductus deferens ascends along the poste-
rior border of the testes and then enters the abdomen in
the spermatic cord, which serves as a conduit for all of the
structures passing to and from the testes. After leaving the
spermatic cord, the ductus deferens descends in the pelvis
to the level of the bladder, where its distal end enlarges
to form the
ampulla
. Surgical disconnection of the vas
deferens in the scrotal area (i.e., vasectomy) serves as an
effective method of male contraception. Because sperm
are stored in the ampulla, men can remain fertile for 4 to
5 weeks after performance of a vasectomy.
Semen Production
The accessory genital glands include the paired seminal
vesicles and bulbourethral glands and the single prostate
gland (see Fig. 39-1).
1,2
These glands secrete fluids that
form the bulk of the ejaculatory fluid or semen.
The seminal vesicles, which lie on the posterior wall of
the bladder, consist of highly tortuous tubes that secrete
fluid for the semen. Each of the paired seminal vesicles is
lined with secretory epithelium containing an abundance
of fructose, prostaglandins, and several other proteins.
The fructose secreted by the seminal vesicles provides the
energy for sperm motility. The prostaglandins are thought
to assist in fertilization by making the cervical mucus
more receptive to sperm and by causing reverse peristaltic
contractions in the uterus and fallopian tubes to move the
sperm toward the ovaries. A short excretory duct from the
each seminal vesicle combines with the ampulla of the duc-
tus deferens to form the ejaculatory duct, which enters the
posterior part of the prostate and continues through until
it ends in the prostatic portion of the urethra. Contraction
of the smooth muscle coat of the seminal vesicles during
ejaculation discharges their secretion into the ejaculatory
ducts and helps to flush sperm out of the urethra.
The prostate, which is the largest of the accessory
glands, is located in the pelvis, inferior to the bladder,
where it surrounds the prostatic portion of the urethra.
The prostate gland secretes a thin, milky, alkaline fluid
containing citric acid, calcium, acid phosphate, a clot-
ting enzyme, and a profibrinolysin.
2
During ejaculation,
the capsule of the prostate contracts, and the added fluid
increases the bulk of the semen. Both vaginal secretions
and the fluid from the vas deferens are strongly acidic.
Because sperm mobilization occurs at a pH of 6.0 to 6.5,
the alkaline nature of the prostatic secretions is essential
for successful fertilization of the ovum.
Surface of
urinary bladder
Penis
Prostatic
urethra
Membranous
urethra
Urethra
Seminiferous
tubules
Testis
Epididymis
Ductus deferens
Urinary bladder opening
Ampulla
Ejaculatory duct
Prostate gland
Seminal vesicle
Spongy
urethra
FIGURE 39-4.
The excretory ducts of the male
reproductive system and the path that sperm
follows as it leaves the testis and travels to the
urethra.
