A n a t o m y a n d h i s t o l o g y o f t h e t e s t e s
F i g u r e 1 6 . 2
Lumen of seminiferous tubule
Spermatic cord
Blood vessels
and nerves
Ductus epididymis
is a coiled tubule
within the epididymis where sperm
mature and acquire motility and the
ability to fertilize an egg.
White fibrous
capsule
covers testis.
Lobule
is an internal
compartment. There
are 200-300 lobules
in a testis.
Seminiferous
tubules
make
sperm.
Leydig cells
(or interstitial
cells) make the hormone
testosterone
.
Blood capillary
Spermatogonium
(stem cell)
Primary spermatocyte
Secondary spermatocyte
Spermatid
Sperm cell or
spermatozoon
Spermatogonia
are stem cells
that become sperm.
Sertoli cells
(or sustentacular ^
cells):
• Support, protect, and defend
developing spermatogenic cells.
• Phagocytize degenerating
spermatogenic cells.
• Secrete fluid for sperm transport.
• Produce the hormone
inhibin
,
which regulates sperm
production.
In sum, the functions of the male reproductive sys-
tems are as follows.
1.
The testes produce sperm and the male sex hormone
testosterone.
2.
The ducts transport, store, and assist in the maturation
of sperm.
3.
The accessory sex glands secrete most of the liquid
portion of semen.
4.
The penis contains the urethra, a passageway for
ejaculation of semen and excretion of urine.
Sperm Production Begins During
Puberty and Continues Throughout Life
Let’s take a closer look at the testes, where sperm is pro-
duced (Figure 16.2). The testes are covered by a dense
white fibrous capsule that extends inward and divides each
testis into internal compartments called lobules. Each of the
200 to 300 lobules contains one to three tightly coiled semi-
niferous tubules that produce sperm, as we’ll discuss soon.
The seminiferous tubules are lined with spermato-
genic (sperm-forming) cells. Positioned against the base-
ment membrane, toward the outside of the tubules, are
the spermatogonia (singular is spermatogonium), the
stem cell precursors of sperm. Toward the lumen of the
tubule are layers of cells in order of advancing maturity:
p rim a ry sperm atocytes, secondary sperm atocytes, sperm atids,
and
sperm cells
(see Figure 16.3). After a sperm cell has formed,
it is released into the lumen of the seminiferous tubule.
Large Sertoli cells, located between the developing
sperm cells in the seminiferous tubules, support, protect,
and nourish spermatogenic cells. They also phagocytize
any degenerating spermatogenic cells, secrete fluid for
sperm transport, and release the hormone inhibin, which
helps regulate sperm production.
Between the seminiferous tubules are clusters of
Leydig cells. These are the cells that secrete the hor-
mone testosterone, the most important androgen. An
androgen is a hormone that promotes the development
of masculine characteristics. Testosterone also promotes
the male’s sex drive.
472 CHAPTER 16
The Reproductive Systems
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