842
UNIT SIX
penis. The subcutaneous tissue of the scrotal wall lacks fat
but contains a layer of smooth muscle F bers that constitute
the
dartos muscle.
Exposure to cold stimulates these mus-
cles to contract, the scrotal skin to wrinkle, and the testes
to move closer to the pelvic cavity, where they can absorb
heat. Exposure to warmth stimulates the F
bers to relax and
the scrotum to hang loosely and provides an environment
3°C (about 5°±) below body temperature, more conducive
to sperm production and survival.
A medial septum divides the scrotum into two cham-
bers, each of which encloses a testis. Each chamber also
contains a serous membrane, which covers the front and
sides of the testis and the epididymis, helping to ensure
that the testis and epididymis move smoothly within the
scrotum (see F
g. 22.4).
PRACTICE
16
Where is the prostate gland located?
17
What are the functions of the prostate gland’s secretion?
18
What is the function of the bulbourethral glands?
19
What are the components of semen?
Male External Reproductive Organs
The male external reproductive organs are the scrotum,
which encloses two testes, and the penis. The urethra passes
through the penis.
Scrotum
The
scrotum
is a pouch of skin and subcutaneous tissue
that hangs from the lower abdominal region posterior to the
M
ale infertility—the inability of sperm
cells to fertilize an egg cell—has sev-
eral causes. If, during fetal develop-
ment, the testes do not descend into the scrotum,
the higher temperature of the abdominal cavity
or inguinal canal causes the developing sperm
cells in the seminiferous tubules to degenerate.
Certain diseases, such as mumps, may inflame
the testes (orchitis), impairing fertility by destroy-
ing cells in the seminiferous tubules.
The quality and quantity of sperm cells are
essential factors in the ability of a man to father
a child. If a sperm head is misshapen, if a sperm
cannot swim, or if there are too few sperm cells,
completing the arduous journey to the well-
protected egg may be impossible. Sometimes
even a sperm cell that enters an egg is unsuccess-
ful because it lacks the microtubules necessary to
attract and merge the nuclei of the two cells.
In the past, sperm analysis was based on
microscopic examination, which was not very
accurate because the human eye cannot easily
follow multiple moving targets. More objective is
computer-aided sperm analysis (CASA), which has
been in use since the late 1980s. CASA can analyze
up to 200 moving sperm in a few seconds, assess-
ing the number of cells per milliliter of seminal F
uid
(density), sperm movement (motility), and the size
and shape of sperm cell parts (morphology).
In a sperm analysis, a man abstains from
intercourse for two to three days, then provides
a sperm sample. This may be done either in a
22.2
CLINICAL APPLICATION
Male Infertility
VCR
Keyboard
Computer
Live image
Printer
Temperature
control
Microscope
Computer monitor/
data display
Video
camera
Digital image
Edge
Centroid
Voltage-complex
analog video signal
Curvilinear
path
Average
path
VSL
BCF
ALH
VAP
VCL
Curvilinear
path
Average
path
VSL
BCF
ALH
VAP
VCL
FIGURE 22A
Computer analysis improves the consistency and accuracy of describing sperm
density, motility, and morphology, each important in diagnosing male infertility.
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