1022
UNIT 5
Continuity
27
The Penis
Describe the location, structure, and function of the
accessory reproductive organs of the male.
Te
penis
(“tail”) is a copulatory organ, designed to deliver
sperm into the female reproductive tract (Figure 27.1 and
Figure 27.5
). Te penis and scrotum, which hang suspended
from the perineum, make up the external reproductive struc-
tures, or
external
genitalia
, of the male.
Te penis consists of an attached root and a free
body
or
shaf
that ends in an enlarged tip, the
glans penis
. Te skin
covering the penis is loose, and when it slides distally it forms
a cuff called the
prepuce
(pre
9
pūs), or
foreskin
, around the
glans. Frequently, the foreskin is surgically removed shortly
a±er birth, a procedure called
circumcision
(“cutting around”).
Interestingly, over 60% of newborn boys in the United States
are circumcised, compared to 15% in other parts of the world.
Circumcision is charged by some as being medically unneces-
sary, but its proponents cite studies showing a 60% reduction
in risk of acquiring HIV (the virus that causes AIDS), as well
as significantly reduced risks for other reproductive system
infections.
²o understand penile anatomy, it is important to know that
its dorsal and ventral surfaces are named in reference to the
erect penis. Internally, the penis contains the spongy urethra
and three long cylindrical bodies (
corpora
) of erectile tissue,
each covered by a sheath of dense fibrous connective tissue.
Tis
erectile tissue
is a spongy network of connective tissue and
smooth muscle riddled with vascular spaces. During sexual ex-
citement, the vascular spaces fill with blood, causing the penis
to enlarge and become rigid. Tis event, called
erection
, enables
the penis to serve as a penetrating organ.
Te midventral erectile body, the
corpus spongiosum
(spon
0
je-o
9
sum; “spongy body”) surrounds the urethra. It ex-
pands distally to form the glans and proximally to form the
the surrounding interstitial fluid. Tus, completely different
cell populations carry out the sperm-producing and hormone-
producing functions of the testis.
Te long
testicular arteries
, which branch from the abdominal
aorta superior to the pelvis (see
gonadal arteries
in Figure 19.24c,
p. 732), supply the testes. Te
testicular veins
draining the tes-
tes arise from a network called the
pampiniform venous plexus
(pam-pin
9
ĭ-form; “tendril-shaped”) that surrounds the portion
of each testicular artery within the scrotum like a climbing vine
(see Figure 27.2). Te cooler venous blood in each pampiniform
plexus absorbs heat from the arterial blood, cooling it before it
enters the testes. In this way, these plexuses help to keep the testes
at their cool homeostatic temperature.
Both divisions of the autonomic nervous system serve the
testes, and when the testes are hit forcefully, associated sensory
nerves transmit impulses that result in agonizing pain and nau-
sea. A connective tissue sheath encloses nerve fibers, blood ves-
sels, and lymphatics. Collectively these structures make up the
spermatic cord
, which passes through the inguinal canal (see
Figure 27.2).
Homeostatic Imbalance
27.1
Although
testicular cancer
is relatively rare (affecting one of
every 50,000 males), it is the most common cancer in young
men ages 15 to 35. A history of mumps or orchitis (inflamma-
tion of the testis) and substantial maternal exposure to envi-
ronmental toxins before birth increase the risk, but the most
important risk factor for this cancer is
cryptorchidism
(nonde-
scent of the testes, see p. 1057).
Every male should examine his testes regularly. Te most
common sign of testicular cancer is a painless solid mass in
the testis. If detected early, testicular cancer has an impressive
cure rate. Over 90% of cases are cured by surgical removal of
the cancerous testis (
orchiectomy
) alone or in combination with
radiation therapy or chemotherapy.
Check Your Understanding
1.
What are the two major functions of the testes?
2.
Which of the tubular structures shown in Figure 27.3a are
the sperm “factories”?
3.
Muscle activity and the pampiniform venous plexus help to
keep the temperature of the testes at homeostatic levels.
How do they do that?
For answers, see Appendix H.
The Male Perineum
Te male
perineum
(per
0
ĭ-ne
9
um; “around the anus”) suspends
the scrotum and contains the root of the penis, and the anus.
More specifically, it is the diamond-shaped region located be-
tween the pubic symphysis anteriorly, the coccyx posteriorly,
and the ischial tuberosities laterally
(Figure 27.4)
.
Te floor
of the perineum is formed by muscles described in Chapter 10
(pp. 344–345).
Scrotum
Penis
Pubic
symphysis
Ischial
tuberosity
Anus
Coccyx
Figure 27.4
The male perineum, inferior view.
previous page 1056 Human Anatomy and Physiology (9th ed ) 2012 read online next page 1058 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off