Chapter 21: Reproductive
System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
21-1
Male Reproductive System
Testes (male gonads) produce sperm,
which mature in the epididymis.
Gland secretions contain fructose for
energy, so sperm can swim.
Sperm with secretions from glands is called
semen.
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The male reproductive system
Fig. 21.1
Secretions are
added by three
glands: seminal
vesicles, prostate
gland, and
bulbourethral
gland.
At ejaculation: sperm leave the
testes  vas deferens  ejaculatory ducts  urethra.
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Testes
Fig. 21.3
Seminiferous tubules (surrounded by testosterone producing
interstitial cells) produce haploid sperm through
spermatogenesis (meiosis).
Sustentacular cells (Sertoli cells) support, nourish, and
regulate the cells during spermatogenesis.
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Sperm anatomy
Stores enzymes
needed to
penetrate the
egg
Fig. 21.3
Sperm do not live more than 48
hours in the female genital
tract.
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Hormonal Regulation in Males
Gonadotropin-releasing hormone (GnRH)
follicle-stimulating hormone (FSH) and
luteinizing hormone (LH).
Inhibin
Testosterone
 = ‘stimulates the release of’
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Hormonal control of testes
Fig. 21.4
Negative
feedback
+
+
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Female Reproductive System
Ovaries (female gonads) usually produce
one egg (or ovum) per month by
oogenesis.
Ovulation is the release of the egg from
the ovary as it enters an oviduct.
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Fig. 21.5
The female reproductive tract
Fimbriae sweep
the egg into an
oviduct with the
help of cilia.
Fertilization
usually takes
place in the
oviduct
Zygote moves to
the uterus, where
it implants in the
uterine lining
(endometrium).
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Female Hormone Levels
The Ovarian Cycle
A female is born with up to 2 million
ovarian follicles (with immature oocytes)
that reduce to 300,000–400,000 by
puberty, but only 400 follicles mature at
the rate of one egg per monthly cycle.
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Two Phases of a 28-day Ovarian Cycle
Follicular phase (day 1-13)
Ovulation occurs on day 14 of a 28-day cycle
Luteal phase (days 15–28)
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Anatomy of ovary and follicle
Fig. 21.7
Follicular Phase
(days 1-13)
Luteal
Phase
(days 15-28)
Egg follicles mature,
from primary follicles to
Graafian follicles.
When the egg is
released, the empty
follicle becomes the
hormone-secreting
corpus luteum.
Ovulation
21-12
(day 14)
Hormonal Regulation in Females
Gonadotropin-releasing hormone (GnRH)
follicle-stimulating hormone (FSH) and
luteinizing hormone (LH).
Estrogen
Progesterone
 = ‘stimulates the release of’
21-13
Hormonal control of ovaries
Fig. 21.8
Estrogen by
itself = Positive
Feedback
+
Negative
Feedback
21-14
The Uterine Cycle
Menstruation (days 1-5)
Proliferative phase (days 6-13)
Ovulation occurs about day 14
Secretory phase (days 15-28)
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Female hormone levels
Estrogen and
progesterone
affect the
endometrium
and control the
uterine cycle.
Fig. 21.9
During
menstruation,
menses occurs
due to the low
levels of
estrogen and
progesterone.
Menses
Proliferative
Secretory
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Fertilization and Pregnancy
If fertilization occurs, the embryo
implants in the endometrium.
No new ovulations occur during this
time.
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Implantation
Placenta  human
chorionic
gonadotropin (HCG)
corpus luteum and
uterine lining
maintained.
Eventually, the
placenta will produce
sufficient estrogen
and progesterone.
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Estrogen and Progesterone
Are important in:
-Development of sex organs
-Maintenance of the secondary sex
characteristics.
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Menopause
Between the ages of 45 and 55, the
ovarian and uterine cycles cease.
The ovaries are no longer responsive to
anterior pituitary hormones (FSH and
LH), and thus no longer produce
estrogen and progesterone.
When menstruation ceases for a year,
menopause is complete.
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Control of Reproduction
Contraceptives are medications and devices
that reduce the chance of pregnancy.
Birth control pills – simulates pregnancy levels
of estrogen and progesterone
Intrauterine device (IUD) - alters the uterine
environment
Diaphragm - is a latex barrier that covers the
cervix - must be used along with spermicidal
jelly or cream
Condom - a latex sheath fitted over the erect
penis.
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Contraceptive implants
use time-release
progesterone, and
Depo-Provera
injections alter the
endometrium to
discourage pregnancy.
Contraceptive vaccines
may be able to utilize
the immune system to
HCG that is necessary
to maintain the embryo.
Fig. 22.12
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Morning-after Pills
A kit called Preven, may be taken up to
72 hours after unprotected intercourse
and upsets the normal uterine cycle,
making implantation unlikely.
Mifepristone (RU-486) is a pill that causes
the loss of an implanted embryo and
may one day be routinely taken if
menstruation is late.
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Infertility
Infertility is the failure of a couple to
achieve pregnancy after one year of
regular, unprotected intercourse.
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Causes of Infertility
Endometriosis, growth of the uterine lining
outside the uterus, or blocked oviducts
due to pelvic inflammatory disease (PID).
Low sperm count and/or production of
abnormal sperm occur due to disease,
radiation, chemicals, high testes
temperature, or psychoactive drugs.
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Assisted Reproductive
Technologies
Alternative methods to assist
reproduction include artificial
insemination by donor and intrauterine
insemination, in vitro fertilization, and
gamete intrafallopian transfer (GIFT),
intracytoplasmic sperm injection, and
surrogate mothers who carry a
pregnancy for another couple.
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Sexually Transmitted Diseases
Sexually transmitted diseases (STDs) are viral
or bacterial in origin and are transmitted
through sexual contact.
The STDs caused by bacteria can be treated
with antibiotics, but those caused by viruses
cannot.
The body does not become immune to STDs.
Center for Disease Control and Prevention:
www.cdc.gov
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AIDS
Acquired immunodeficiency syndrome
(AIDS) is caused by the retrovirus HIV
whose primary host is helper T cells.
21-28
Reproduction of HIV
21-29
Phases of an HIV Infection
During Category A: Acute Phase, the CD4
T lymphocyte count is 500 per mm3 or
greater.
By the Category B: Chronic phase, the
CD4 T cell count is 200–499 per mm3.
By the Category C: AIDS stage, the CD4
T cell count is below 200 per mm3.
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Treatment for HIV
There is no cure for AIDS but highly
active antiretroviral therapy (HAART)
stops the progress of AIDS in the
chronic stage for a number of years.
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Other STD’s
Genital herpes  herpes simplex virus
type 2
Genital warts  human papillomaviruses
(HPVs).
Gonorrhea  by the bacterium Neisseria
gonorrhoeae.
Syphilis  by the bacterium Treponema
pallidum
21-32
Hepatitis Infections
There are a number of hepatitis infections.
Hepatitis A (viral infection) is normally
acquired from drinking sewagecontaminated water, but may also be
spread through oral/anal contact.
Hepatitis B is spread by sexual contact.
Hepatitis C is spread through transfusion.
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Chlamydia
Chlamydia (bacterium Chlamydia
trachomatis) infections are more
numerous than any other sexually
transmitted disease.
Symptoms may appear to be a urinary
tract infection with a mild burning
sensation upon urination.
21-34