869
CHAPTER TWENTY-TWO
Reproductive System
Certain subtypes of human papilloma virus (HPV) are responsible for
genital warts and nearly all cases of cervical cancer. A vaccine that
became available in 2006 consists of proteins from HPV types 6, 11,
16, and 18. The vaccine stimulates the immune system to manu-
facture antibodies against the viruses, and it cannot cause cancer
because it does not contain viral DNA. The HPV vaccine, marketed as
Gardasil, is administered in three doses over a six-month period, and
is most eF
ective if given to 9 to 15 year old girls. Women aged 16 to
26 can also bene±
t from the vaccine.
PRACTICE
66
Why are sexually transmitted diseases also called sexually
transmitted infections?
67
Why are sexually transmitted diseases sometimes di²
cult to
diagnose?
68
What are some common symptoms of sexually transmitted diseases?
One possible complication of the STDs gonorrhea and
chlamydia is
pelvic infl
ammatory disease,
in which bacte-
ria enter the vagina and spread throughout the reproductive
organs. The disease begins with intermittent cramps, fol-
lowed by sudden fever, chills, weakness, and severe cramps.
Hospitalization and intravenous antibiotics can stop the
infection. The uterus and uterine tubes are often scarred,
resulting in infertility and increased risk of ectopic preg-
nancy, in which the embryo develops in a uterine tube.
Acquired immune def
ciency syndrome
(AIDS) is a steady
deterioration of the body’s immune defenses in which the
body becomes overrun by infection and often cancer. The
human immunodeF
ciency virus (HIV) that causes AIDS is
transmitted in body fl uids such as semen, blood, and milk.
It is most frequently passed during unprotected intercourse
or by using a needle containing contaminated blood. Clinical
Application 16.1 (pp. 636–637) explores HIV infection.
(2) The seminiferous tubules unite to form the rete
testis that joins the epididymis.
(3) The seminiferous tubules contain
undifferentiated cells that give rise to sperm
cells.
(4) The interstitial cells that produce male sex
hormones are between the seminiferous
tubules.
c. ±ormation of sperm cells
(1) The epithelium lining the seminiferous tubules
includes sustentacular cells and spermatogenic
cells.
(a) The sustentacular cells support and
nourish the spermatogenic cells.
(b) The spermatogenic cells give rise to
spermatogonia.
(2) Spermatogenesis produces sperm cells from
spermatogonia that have differentiated to
become primary spermatocytes.
(a) Spermatogensis produces four sperm cells
from each primary spermatocyte.
(b) Meiosis halves the number of
chromosomes in sperm cells (46 to 23).
(3) Membranous processes of adjacent
sustentacular cells form a barrier in the
epithelium.
(a) The barrier separates early and late stages
of spermatogenesis.
(b) It helps provide a favorable environment
for differentiating cells.
d. Structure of a sperm cell
(1) The sperm head contains a nucleus with 23
chromosomes.
(2) The sperm body has many mitochondria.
(3) The sperm tail propels the cell.
CHAPTER SUMMARY
22.1
INTRODUCTION (PAGE 831)
1. Reproductive organs produce sex cells and sex
hormones, nurture these cells and transport them.
2. Sex cells are produced by meiosis consisting of
two divisions, each progressing through prophase,
metaphase, anaphase, and telophase.
a. In the F
rst meiotic division, homologous,
replicated chromosomes (each consisting of
two chromatids held together by a centromere)
separate, and their number is halved.
b. In the second meiotic division, the chromatids
part, producing four haploid cells.
c. Meiosis leads to genetic variability because of the
random alignment of maternally and paternally
derived chromosomes in metaphase I and crossing
over.
22.2
ORGANS OF THE MALE REPRODUCTIVE
SYSTEM (PAGE 833)
The primary male sex organs are the two testes, which
produce sperm cells and male sex hormones. Accessory
organs are internal and external.
1. Testes
a. Descent of the testes
(1) Testes originate posterior to the parietal
peritoneum near the level of the developing
kidneys.
(2) The gubernaculum guides the descent of the
testes into the lower abdominal cavity and
through the inguinal canal.
(3) Undescended testes cannot produce
sperm cells because of the high abdominal
temperature.
b. Structure of the testes
(1) The testes are lobules separated by connective
tissue and F
lled with seminiferous tubules.
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