1024
UNIT 5
Continuity
27
vas”). In this relatively minor operation, the physician makes
a small incision into the scrotum and then cuts through and
ligates (ties off) each ductus deferens. Sperm are still produced,
but they can no longer reach the body exterior. Eventually, they
deteriorate and are phagocytized. Vasectomy is simple and pro-
vides highly effective birth control (close to 100%). For those
wishing to reverse that procedure, the success rate is about 50%.
The Urethra
Te
urethra
is the terminal portion of the male duct system
(Figures 27.1 and 27.5). It conveys both urine and semen (at
different times), so it serves both the urinary and reproductive
systems. Its three regions are:
Prostatic urethra
, the portion surrounded by the prostate
Intermediate part of the urethra
(or membranous urethra) in
the urogenital diaphragm
Spongy urethra
, which runs through the penis and opens to
the outside at the
external urethral orifice
Te spongy urethra is about 15 cm (6 inches) long and accounts
for 75% of urethral length. Its mucosa contains scattered
ure-
thral glands
that secrete lubricating mucus into the lumen just
before ejaculation.
Check Your Understanding
4.
What is the function of the erectile tissue of the penis?
5.
Name the organs of the male duct system in order, from the
epididymis to the body exterior.
6.
What are two functions of the stereocilia on the epididymal
epithelium?
7.
Which accessory organ of the male duct system runs from
the scrotum into the abdominal cavity?
For answers, see Appendix H.
The Male Accessory Glands
Discuss the sources and functions of semen.
Te
accessory glands
include the paired seminal glands and
bulbo-urethral glands and the single prostate (Figures 27.1 and
27.5). ±ogether these glands produce the bulk of
semen
(sperm
plus accessory gland secretions).
The Seminal Glands
Te
seminal glands
(sem
9
ĭ-nul), or
seminal vesicles
, lie on
the posterior bladder surface. Each of these fairly large, hollow
glands is about the shape and length (5–7 cm) of a little fin-
ger. However, because a seminal gland is pouched, coiled, and
folded back on itself, its uncoiled length is actually about 15 cm.
Its fibrous capsule encloses a thick layer of smooth muscle that
contracts during ejaculation to empty the gland.
Te seminal gland mucosa is a secretory pseudostratified
columnar epithelium. Stored within the mucosa’s honeycomb
of crypts and blind alleys is a yellowish viscous alkaline fluid
containing fructose sugar, citric acid, a coagulating enzyme
The Male Duct System
As we mentioned earlier, sperm travel from the testes to the
body exterior through a system of ducts. In order (proximal to
distal), the
accessory ducts
are the epididymis, ductus deferens,
ejaculatory duct, and urethra.
The Epididymis
Te cup-shaped
epididymis
(
epi
5
beside;
didym
5
the testes)
is about 3.8 cm (1.5 inches) long (Figures 27.1 and 27.3a, b). Its
head
, which contains the efferent ductules, caps the superior
aspect of the testis. Its
body
and
tail
are on the posterolateral
area of the testis.
Most of the epididymis consists of the highly coiled
duct of
the epididymis
, which has an uncoiled length of about 6 m (20
feet). Some pseudostratified epithelial cells of the duct mucosa
exhibit long, nonmotile microvilli (
stereocilia
). Te huge surface
area of these stereocilia allows them to absorb excess testicular
fluid and to pass nutrients to the many sperm stored temporar-
ily in the lumen.
Te immature, nearly nonmotile sperm that leave the testis
are moved slowly along the duct of the epididymis through fluid
that contains several kinds of antimicrobial proteins, including
defensins. As they move along its tortuous course (a trip that
takes about 20 days), the sperm gain the ability to swim.
Sperm are ejaculated from the epididymis, not the testes as
many believe. When a male is sexually stimulated and ejacu-
lates, the smooth muscle in the ducts of the epididymis con-
tracts, expelling sperm into the next segment of the duct system,
the
ductus deferens
.
Sperm can be stored in the epididymis for several months. If
they are held longer, epithelial cells of the epididymis eventually
phagocytize them. Tis is not a problem for the man, as sperm
are generated continuously.
The Ductus Deferens and Ejaculatory Duct
Te
ductus deferens
(duk
9
tus def
9
er-ens; “carrying away”), or
vas deferens
, is about 45 cm (18 inches) long. It runs upward
as part of the spermatic cord from the epididymis through the
inguinal canal into the pelvic cavity (Figure 27.1). Easily pal-
pated as it passes anterior to the pubic bone, it then loops medi-
ally over the ureter and descends along the posterior bladder
wall. Its terminus expands to form the
ampulla
of the ductus
deferens and then joins with the duct of the seminal gland to
form the short
ejaculatory duct
. Each ejaculatory duct enters
the prostate, and there it empties into the urethra.
Like that of the epididymis, the mucosa of the ductus def-
erens is pseudostratified epithelium. However, its muscu-
lar layer is extremely thick and the duct feels like a hard wire
when squeezed between the fingertips. During ejaculation, the
smooth muscle in its walls creates strong peristaltic waves that
rapidly squeeze the sperm forward along the tract and into the
urethra.
As Figure 27.3 illustrates, part of the ductus deferens lies in
the scrotal sac. Some men opt to take full responsibility for birth
control by having a
vasectomy
(vah-sek
9
to-me; “cutting the
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