841
CHAPTER TWENTY-TWO
Reproductive System
ment vary greatly from individual to individual. In
some men, the recommended course is “watch-
ful waiting,” continuing to have frequent check-
ups to monitor the enlargement, but not acting
until symptoms arise. Surgery to treat prostate
cancer is highly eF
ective. It once commonly left
a man incontinent and with erectile dysfunc-
tion. However, control of urination often returns
within a few weeks, and newer surgical methods
preserve the nerves necessary for erection.
and urinary bladder with a device inserted through
the penis, called a cytoscope; as well as a blood test
to detect elevated prostate speci±
c antigen (PSA),
a cell surface protein normally found on prostate
cells. Elevated PSA levels indicate an enlarged pros-
tate, possibly from a benign or cancerous growth.
Ultrasound may provide further information on
whether a benign or cancerous growth is present.
Table 22A summarizes treatments for an
enlarged prostate. The components of treat-
T
he prostate gland is small in boys, begins
to grow in early adolescence, and reaches
adult size several years later. An adult’s
prostate gland is about the size of a walnut.
Usually, the gland does not grow again until age
±
fty, when in half of all men, it enlarges enough
to press on the urethra. This condition is called
benign prostatic hypertrophy (BPH). As many
as 90% of men over age seventy may have BPH.
It produces a feeling of pressure on the bladder
because it cannot empty completely, and the
man feels the urge to frequently urinate. An early
sign may be dribbling after urination. Retained
urine can lead to infection and inflammation,
bladder stones, or kidney disease.
Medical researchers do not know what causes
prostate enlargement. Risk factors include a fatty
diet, having had a vasectomy, possible occupa-
tional exposure to batteries or the metal cadmium,
and inheriting a particular gene that also causes
breast cancer. The enlargement may be benign
or cancerous. Prostate cancer is highly treatable if
detected early, so men should have their prostates
examined regularly. ²our out of ±
ve men who have
prostate cancer are over age sixty-±
ve.
Diagnostic tests for prostate cancer include a
rectal exam; visualization of the prostate, urethra,
22.1
CLINICAL APPLICATION
Prostate Enlargement
The volume of semen released at one time varies from
2 to 5 milliliters. The average number of sperm cells in the
uid is about 120 million per milliliter.
Sperm cells remain nonmotile while they are in the ducts
of the testis and epididymis, but begin to swim as they mix
with the secretions of accessory glands. However, sperm cells
cannot fertilize an egg cell until they enter the female repro-
ductive tract. Here, they undergo
capacitation,
which weak-
ens the acrosomal membranes of the sperm cells. When sperm
cells are placed with egg cells in a laboratory dish to achieve
fertilization—a technique called
in vitro
fertilization, discussed
in From Science to Technology 23.1 (p. 878)—chemicals are
added to simulate capacitation.
Although sperm cells can live for many weeks in the ducts
of the male reproductive tract, they usually survive only up to
six days after being expelled to the outside, even when they are
maintained at body temperature. (The ability of a sperm cell to
fertilize an oocyte generally lasts only twenty-four to forty-eight
hours after the sperm enter the femal reproductive tract.) On
the other hand, sperm cells can be stored and kept viable for
years if they are frozen at a temperature below –100°C. Clinical
Application 22.2 describes some causes of male infertility.
Bulbourethral Glands
The
bulbourethral
(bul
bo-u-re
thral)
glands
(Cowper’s
glands) are two small structures, each about a centimeter in
diameter. They are inferior to the prostate gland lateral to
the membranous urethra and are enclosed by muscle ±
bers
of the urogenital diaphragm (see ±
g. 22.4).
The bulbourethral glands are composed of many tubes
whose epithelial linings secrete a mucuslike fl
uid. This fl uid
is released in response to sexual stimulation and lubricates
the end of the penis in preparation for sexual intercourse
(coitus). However, females secrete most of the lubricating
fl uid for intercourse.
Semen
The fl
uid the urethra conveys to the outside during ejacu-
lation is called
semen
(se
men). It consists of sperm cells
from the testes and secretions of the seminal vesicles, pros-
tate gland, and bulbourethral glands. Semen is slightly
alkaline (pH about 7.5), and it includes prostaglandins and
nutrients.
TABLE
22A
|
Some Medical Treatments for an Enlarged
Prostate Gland
Surgical removal of prostate
Radiation
Drug (Proscar, or ±
nasteride) to block testosterone’s growth-stimulating eF
ect on the prostate
Alpha blocker drugs, which relax muscles near the prostate, relieving pressure
Microwave energy delivered through a probe inserted into the urethra or rectum
Balloon inserted into the urethra and in³
ated with liquid
Tumor frozen with liquid nitrogen delivered by a probe through the skin
Device (stent) inserted between lobes of prostate to relieve pressure on the urethra
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