1020
UNIT 5
Continuity
27
Furthermore, the scrotum is affected by temperature changes.
When it is cold, the testes are pulled closer to the pelvic floor
and the warmth of the body wall, and the scrotum becomes
shorter and heavily wrinkled, decreasing its surface area and
increasing its thickness to reduce heat loss. When it is warm,
the scrotal skin is flaccid and loose to increase the surface area
for cooling (sweating) and the testes hang lower, away from the
body trunk.
Tese changes in scrotal surface area help maintain a fairly
constant intrascrotal temperature and reflect the activity of two
sets of muscles that respond to ambient temperature. Te
dar-
tos muscle
(dar
9
tos; “skinned”), a layer of smooth muscle in
the superficial fascia, wrinkles the scrotal skin. Te
cremaster
muscles
(kre-mas
9
ter; “a suspender”), bands of skeletal muscle
that arise from the internal oblique muscles of the trunk, elevate
the testes.
The Testes
Each plum-sized testis is approximately 4 cm (1.5 inches) long
by 2.5 cm (1 inch) wide and is surrounded by two tunics. Te
outer tunic is the two-layered
tunica vaginalis
(vaj
0
ĭ-nal
9
is),
derived from an outpocketing of the peritoneum (Figure 27.2
and
Figure 27.3a
). Deep to this serous layer is the
tunica al-
buginea
(al
0
bu-jin
9
e-ah; “white coat”), the fibrous capsule of
the testis.
Septa extending inward from the tunica albuginea divide
the testis into about 250 wedge-shaped
lobules
(Figure 27.3).
Each contains one to four tightly coiled
seminiferous tubules
(sem
0
ĭ-nif
9
er-us; “sperm-carrying”), the actual “sperm fac-
tories” consisting of a thick stratified epithelium surrounding
a central fluid-containing lumen. Te epithelium consists of
spheroid
spermatogenic
(“sperm-forming”)
cells
, embedded in
substantially larger columnar cells called
sustentocytes
. Te sus-
tentocytes are supporting cells that play several roles in sperm
formation as described shortly.
Surrounding each seminiferous tubule are three to five layers
of smooth muscle–like
myoid cells
(Figure 27.3c). By contract-
ing rhythmically, myoid cells may help to squeeze sperm and
testicular fluids through the tubules and out of the testes.
Te seminiferous tubules of each lobule converge to form a
straight tubule
that conveys sperm into the
rete testis
(re
9
te), a
tubular network on the posterior side of the testis. From the rete
testis, sperm leave the testis through the
efferent ductules
and
Penis
Internal spermatic
fascia
Superficial inguinal ring
(end of inguinal canal)
Urinary bladder
Spermatic cord
Ductus (vas)
deferens
Autonomic
nerve fibers
Testicular artery
Epididymis
Pampiniform
venous plexus
Tunica vaginalis
(from peritoneum)
Tunica albuginea
of testis
Septum of scrotum
Cremaster muscle
External spermatic
fascia
Superficial fascia
containing
dartos muscle
Skin
Scrotum
Figure 27.2
Relationships of the testis to the scrotum and spermatic cord.
The scrotum
has been opened and its anterior portion removed.
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