722 Chapter 20
present sites for inflammatory reactions in which spermatozoa
are phagocytosed and destroyed by the immune system. It is thus
not surprising that approximately 70% of men with vasectomies
develop antisperm antibodies. These antibodies do not appear to
cause autoimmune damage to the testes, but they do significantly
diminish the possibility of reversing a vasectomy and restoring
fertility.sperm per milliliter of ejaculate. Normal human semen values
are summarized in table 20.5.
A sperm concentration below about 20 million per millili-
ter is termed oligospermia ( oligo 5 few) and is associated with
decreased fertility. A total sperm count below about 40 million per
ejaculation is clinically significant in male infertility. Oligosper-
mia may be caused by a variety of factors including heat from a
sauna or hot tub, various pharmaceutical drugs, lead and arsenic
poisoning, and such illicit drugs as marijuana, cocaine, and ana-
bolic steroids. It may be temporary or permanent. In addition to
low sperm counts as a cause of infertility, some men and women
have antibodies against sperm antigens (this is very common in
men with vasectomies). While such antibodies do not appear to
affect health, they do reduce ferility.
Use of condoms is the most widely practiced reversible method
of male contraception. Use of hormones to achieve male contra-
ception, analogous to the female birth control pill (section 20.5),
involves androgens and sometimes progesterone to suppress FSH
and LH. Although this method works to reduce spermatogenesis
to infertile levels, its side effects have prevented it from becom-
ing available to the public. The development of male contracep-
tive pills is hindered by the large daily production of sperm and
by the blood-testis barrier. However, research into reversible
male contraception is ongoing. In a recent report, scientists dem-
onstrated success with a new drug that blocks a molecule needed
for chromatin remodeling during spermatogenesis.
One of the most widely used methods of male contraception
is a surgical procedure called a vasectomy ( fig. 20.22 ). In this pro-
cedure, each ductus (vas) deferens is cut and tied or, in some cases,
a valve or similar device is inserted. A vasectomy interferes with
sperm transport but does not directly affect the secretion of andro-
gens from Leydig cells in the interstitial tissue. Spermatogenesis
continues, but the sperm cannot be drained from the testes; as a
result, the sperm accumulate in “crypts” that form in the semi-
niferous tubules, epididymis, and ductus deferens. These crypts
Table 20.5 | Semen Analysis
Characteristic Reference Value
Volume of ejaculate 1.5–5.0 ml
Sperm count 40–250 million/ml
Sperm motility
Percentage of motile forms:
1 hour after ejaculation 70% or more
3 hours after ejaculation 60% or more
Leukocyte count 0–2,000/ml
pH 7.2–7.8
Fructose concentration 150–600 mg/100 mlSource: Modified from L. Glasser,“Seminal Fluid and Subfertility,” Diagnostic
Medicine, July/August 1981, p. 28. Used by permission. Other sources
provide slightly different ranges.
Figure 20.22 A vasectomy. In this surgical procedure
a segment of the ductus (vas) deferens is removed through an
incision in the scrotum.(a)(b)(c) (d)| CHECKPOINT
5a. Describe the effects of castration on FSH and LH
secretion in the male. Explain the experimental
evidence suggesting that the testes produce a
polypeptide that specifically inhibits FSH secretion.
5b. Describe the two compartments of the testes with
respect to (a) structure, (b) function, and (c) response
to gonadotropin stimulation. Describe two ways in
which these compartments interact.
6a. Using a diagram, describe the stages of
spermatogenesis. Why can spermatogenesis
continue throughout life without using up all of the
spermatogonia?
6b. Describe the structure and proposed functions of the
Sertoli cells in the seminiferous tubules.- Describe the roles of FSH and testosterone in
spermatogenesis during and after puberty.
20.4 FEMALE REPRODUCTIVE
SYSTEM
Some ovarian follicles mature during the ovarian cycle, and
the ova they contain progress to the secondary oocyte stage
of meiosis. At ovulation, usually one secondary oocyte is