840
UNIT SIX
As sperm move through the ductus deferens into the
ejaculatory duct, the contents of the seminal vesicles empty
into the ejaculatory ducts. This greatly increases the volume
of the fl
uid discharged from the ductus deferens.
PRACTICE
13
Describe the structure of the epididymis.
14
Trace the path of the ductus deferens.
15
What is the function of a seminal vesicle?
Prostate Gland
The
prostate
(pros
ta
¯t)
gland
(see
f
gs.
22.4 and
22.14
) is a
chestnut-shaped structure about 4 centimeters across and 3
centimeters thick that surrounds the proximal portion of the
urethra, just inferior to the urinary bladder. It is composed of
many branched tubular glands enclosed in connective tissue.
Septa of connective tissue and smooth muscle extend inward
from the capsule, separating the tubular glands. The ducts of
these glands open into the urethra.
The prostate gland secretes a thin, milky fl uid. This alka-
line secretion neutralizes the fluid containing sperm cells,
which is acidic from accumulation of metabolic wastes from
the sperm cells. Prostatic fl uid also enhances the motility of
sperm cells, which remain relatively nonmotile in the acidic
contents of the epididymis. In addition, the prostatic fluid
helps neutralize the acidic secretions of the vagina, helping to
sustain sperm cells that enter the female reproductive tract.
The prostate gland releases its secretions into the ure-
thra as smooth muscles contract in its capsular wall. As
this release occurs, the contents of the ductus deferens and
the seminal vesicles enter the urethra, which increases the
volume of the fl
uid. Clinical Application 22.1 discusses the
effects of prostate enlargement.
part of the spermatic cord. It passes through the inguinal
canal, enters the abdominal cavity outside the parietal peri-
toneum, and courses over the pelvic brim. From there, it
extends backward and medially into the pelvic cavity,
where it ends behind the urinary bladder.
Near its termination, the ductus deferens dilates into a
portion called the
ampulla.
Just outside the prostate gland, the
tube becomes slender again and unites with the duct of a semi-
nal vesicle. The fusion of these two ducts forms an
ejaculatory
duct,
which passes through the prostate gland and empties
into the urethra through a slitlike opening (see ± g. 22.4).
Seminal Vesicles
The
seminal vesicles
(see ±
g. 22.4) are convoluted, saclike
structures about 5 centimeters long each attached to the
ductus deferens near the base of the urinary bladder. The
glandular tissue lining the inner wall of the seminal vesicle
secretes a slightly alkaline fl
uid. This fl
uid helps regulate the
pH of the tubular contents as sperm cells travel to the out-
side. The secretion of the seminal vesicle also contains
fruc-
tose,
a monosaccharide that provides energy to the sperm
cells, and
prostaglandins,
which stimulate muscular contrac-
tions of the female reproductive organs, aiding the move-
ment of sperm cells toward the egg cell.
Epithelium
Lumen
Smooth
muscle
Sperm in lumen of
ductus deferens
Pseudostratified colum-
nar epithelium
Smooth muscle
FIGURE 22.13
Ductus (vas) deferens. (
a
) Micrograph of a cross
section of the ductus deferens (40×). (
b
) Light micrograph of the wall of
the ductus deferens (400×).
(a)
(b)
Secretory cells of the
prostate gland
Smooth muscle
Lumen of urethra
FIGURE 22.14
Light micrograph of the prostate gland (10×).
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