Download Chapter 21: Reproductive System

Chapter 21: Reproductive
System
21-1
Male Reproductive System
Genital Tract
In males the testes, held outside the body
in the scrotum, produce sperm.
Sperm mature in coiled tubes atop each
testis, called the epididymis (plural,
epididymides).
At ejaculation, sperm leave the testes
through the vas deferens (plural, vasa
deferentia), and pass through the
ejaculatory ducts to the urethra.
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Along the way, secretions (seminal fluid)
are added from three glands: two
seminal vesicles, the donut-shaped
prostate gland at the base of the
urinary bladder, and paired
bulbourethral glands.
These glands add frustose for energy so
sperm can swim, and prostaglandins
that cause uterine contractions; the
secretions are slightly basic.
Sperm with secretions from these glands
is called semen.
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The male reproductive system
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Orgasm in Males
The penis, the organ of sexual,
intercourse, becomes erect from sexual
arousal that stimulates cGMP in smooth
muscle cells to allow erectile tissue to
fill with blood; arterioles dilate and veins
are compressed.
Orgasm involves ejaculation and
muscular tension followed by muscular
contractions and relaxation.
Over 400 million sperm may be in each
ejaculate.
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Penis anatomy
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Male Gonads, the Testes
The testes, which produce sperm and
male sex hormones, contain
seminiferous tubules surrounded by
interstitial cells.
Testes originate in the abdominal cavity
but descend into the scrotum where it
is cool enough for sperm development.
Testes that do not descend must be
treated surgically otherwise sterility will
result.
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Seminiferous Tubules
Seminiferous tubules inside the testes
produce haploid sperm through
spermatogenesis.
Sustentacular cells (Sertoli cells)
support, nourish, and regulate the cells
during spermatogenesis.
Sperm have a head, middle piece, and
tail.
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Testes
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The head of the sperm is covered by a
cap called the acrosome which stores
enzymes needed to penetrate the egg.
Sperm do not live more than 48 hours in
the female genital tract.
Interstitial cells that lie between the
seminiferous tubules within testes
produce testosterone.
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Sperm anatomy
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Hormonal Regulation in Males
In both males and females, gonadotropinreleasing hormone, or GnRH, secreted
by the hypothalamus stimulates the
anterior pituitary to release folliclestimulating hormone (FSH) and
luteinizing hormone (LH).
FSH stimulates the seminiferous tubules
to produce sperm and the hormone
inhibin.
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LH stimulates interstitial cells to produce
testosterone.
Testosterone brings about and maintains
the male secondary sex characteristics.
Testosterone exerts feedback control
over the hypothalamus and anterior
pituitary resulting in a constant amount
of hormones and sperm production
over time.
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Hormonal control of testes
21-14
Female Reproductive System
The female gonads are the ovaries.
The ovaries usually produce one egg (or
ovum) per month during the process of
oogenesis.
Ovulation is the release of the egg from
the ovary as it enters an oviduct.
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The Genital Tract
The oviducts that extend from the ovaries
to the uterus have finger-like
projections or fimbriae that sweep the
egg into an oviduct with the help of
cilia.
Fertilization usually takes place in the
oviduct; the zygote moves by ciliary
movement and oviduct contractions to
the uterus, where it implants in the
uterine lining (endometrium).
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The pear-shaped uterus is thick-walled
and muscular.
The lower end of the uterus is the cervix
that opens into the vagina.
The vagina facilitates sexual intercourse,
serves as the birth canal, and acts as
an exit for menstrual flow.
A Pap test allows microscopic
examination of the cervix tissue for
cancer cells.
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The female reproductive tract
21-18
External Genitals
The external genital area of the female is
the vulva and includes the vaginal
opening, urethral opening, clitoris,
labia minora, and labia majora.
The vagina may be partially closed by a
ring of tissue called the hymen.
The reproductive and urinary systems in
females are completely separate.
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External genitals of the female
21-20
Orgasm in Females
Upon sexual stimulation, the labia,
vaginal walls, and clitoris become
engorged with blood.
The clitoris is extremely sensitive, and
orgasm occurs at the height of the
sexual response.
In contrast to the male penis, there is no
refractory period, and multiple orgasms
can occur during a single sexual
experience.
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Female Hormone Levels
The Ovarian Cycle
An ovary has an outer cortex and an inner
medulla; the cortex is where egg cells lie.
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.
The ovarian cycle is under the control of
FSH and LH.
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Anatomy of ovary and follicle
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Egg follicles mature, from primary
follicles to Graafian follicles.
When the egg is released, the empty
follicle becomes the hormone-secreting
corpus luteum.
The ovaries produce the female sex
hormones estrogen and progesterone.
Estrogen and progesterone exert
feedback control over the
hypothalamus and the anterior pituitary
causing the cycle to begin again.
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During a follicular phase (day 1-13), FSH
from the anterior pituitary stimulates
development of an oocyte-containing
follicle which secretes estrogen and
progesterone.
Ovulation occurs on day 14 of a 28-day
cycle.
During a luteal phase (days 15–28), the
corpus luteum develops under the
influence of LH and secretes
progesterone and estrogen to promote
the development of the endometrium.
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Hormonal control of ovaries
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The Uterine Cycle
The female sex hormones, estrogen and
progesterone, affect the endometrium,
causing the uterus to undergo a
cyclical series of events called the
uterine cycle.
During menstruation (days 1-5), menses
occurs due to the low levels of
estrogen and progesterone in the
blood.
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During a proliferative phase (days 6-13),
the endometrium thickens.
Ovulation occurs about day 14.
During a secretory phase (days 15-28),
the endometrium continues to thicken
and becomes vascular.
If pregnancy does not occur the cycle
begins again.
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Female hormone levels
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Fertilization and Pregnancy
If fertilization occurs, the embryo
implants in the endometrium.
The placenta begins to produce human
chorionic gonadotropin (HCG), which
maintains the corpus luteum and the
uterine lining is maintained.
Eventually, the placenta will produce
sufficient estrogen and progesterone.
No new ovulations occur during this
time.
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Implantation
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Estrogen and Progesterone
At puberty, sex hormones (primarily
estrogen) stimulate development of sex
organs and maintain the secondary sex
characteristics.
Estrogen is primarily responsible for
female fat distribution.
Both estrogen and progesterone are
needed for breast development.
Females have a wider pelvic girdle than
males.
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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, 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 Methods
Oral contraception (birth control pills)
prevent ovulation by simulating
pregnancy levels of estrogen and
progesterone.
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The intrauterine device (IUD) alters the
uterine environment so fertilization
and/or implantation cannot take place.
A diaphragm is a latex barrier that covers
the cervix; a cervical cap is a minidiaphragm.
The diaphragm must be used along with
spermicidal jelly or cream.
The male condom is 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.
An antisperm vaccine may also be
possible.
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Various birth control devices
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Morning-after Pills
A kit called Preven, made up of four
synthetic progesterone pills, may be
taken up to 72 hours after unprotected
intercourse.
This 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.
The American Medical Association
estimates that 15% of all couples are
infertile.
The cause of infertility can be attributed
to the male (40%), the female (40%), or
both (20%).
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Causes of Infertility
Infertility in females is often caused by
endometriosis, growth of the uterine lining
outside the uterus, or blocked oviducts
due to pelvic inflammatory disease (PID).
In males, a low sperm count and/or
production of abnormal sperm occur due
to disease, radiation, chemicals, high
testes temperature, or psychoactive drugs.
Vasectomies are difficult to reverse, also
leading to male infertility.
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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 (AIDS, genital warts, genital
herpes) or bacterial (gonorrhea,
chlamydia, syphilis) 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.
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AIDS
Acquired immunodeficiency syndrome
(AIDS) is caused by the retrovirus HIV
whose primary host is helper T cells.
HIV attaches to a CD4 receptor in the host
cell membrane; then the viral enzyme
reverse transcriptase copies viral RNA
into DNA, which integrates itself into a
host chromosome.
At the time of viral reproduction, host DNA
produces many copies of viral RNA and
protein synthesis produces capsid
proteins.
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Reproduction of HIV
21-44
Phases of an HIV Infection
During Category A: Acute Phase, the
helper T lymphocyte count is 500 per
mm3 or greater.
The immune system can still function
normally and no serious symptoms
appear.
The patient is highly infectious but does
not have antibodies and therefore tests
negative for HIV.
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By the Category B: Chronic phase, the
helper T cell count is 200–499 per mm3.
The lymph nodes are swollen, a person
has severe fatigue, recurrent fevers,
night sweats, and a persistent cough
and diarrhea.
Toward the end of this phase, infections
like thrush, and/or herpes simplex occur.
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By the Category C: AIDS stage, the CD4
T cell count is below 200 per mm3.
Opportunistic infections develop, such
as: Pneumocystis carinii pneumonia,
Mycobacterium tuberculosis,
toxoplasmosic encephalitis, Kaposi’s
sarcoma, and invasive cervical cancer.
Treatment is successful for a while but
death usually occurs 2–4 years
following the AIDS stage.
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The course of an AIDS infection
21-48
Treatment for HIV
There is no cure for AIDS but highly
active antiretroviral therapy (HAART),
which combines the administration of
two inhibitors of reverse transcriptase
with a protease that prevents assembly,
stops the progress of AIDS in the
chronic stage for a number of years.
Research into various vaccine strategies
is now being pursued.
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Genital Herpes
Genital herpes is caused by herpes
simplex virus type 2 and occasionally
type 1 which usually causes cold sore.
Blisters are followed by painful ulcers,
which can clear up and reappear later.
Infants born vaginally to women with
genital herpes may contract herpes,
causing grave illness, blindness,
neurological disorders, or death.
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Genital herpes
21-51
Genital Warts
Genital warts are caused by human
papillomaviruses (HPVs).
Warts need not be visible on penis or
vaginal opening.
Genital warts are associated with cancer
of cervix; teenagers with multiple sex
partners are especially susceptible to
cervical cancer.
Genital warts are not curable at this time.
A newborn can become infected during
vaginal birth.
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Genital warts
21-53
Hepatitis Infections
There are a number of hepatitis infections.
Hepatitis A is normally acquired from
drinking sewage-contaminated 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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Hepatitis B
Hepatitis B virus (HBV) is more likely to
be spread by sexual contact than the
HIV virus.
Flu-like symptoms and jaundice may be
present.
A chronic form of the disease can lead to
liver failure.
An HBV vaccine is now available and a
part of the routine immunizations for
children.
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Chlamydia
Chlamydia 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.
If not treated pelvic inflammatory disease
(PID), sterility, or ectopic pregnancy
can result.
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Chlamydial infection
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Detection and Treatment of
Chlamydia
Tests for detection of chlamydia are
expensive and may not be readily
available.
Physicians can use several criteria aside
from detection of the organism to
decide whether to prescribe the proper
antibiotics to cure chlamydia.
If gonorrhea is present, some physicians
also routinely prescribe antibiotics for
chlamydia.
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Gonorrhea
Gonorrhea is caused by the bacterium
Neisseria gonorrhoeae.
Most males complain of pain on urination
and there is a discharge.
Females are asymptomatic and may
develop PID.
Infants can be infected during vaginal
birth; silver nitrate or antibiotics in the
eyes are standard treatment.
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Gonorrhea
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Syphilis
Syphilis, caused by a bacterium
Treponema pallidum, has three stages.
In the primary stage, a chancre forms at
site of infection.
In the secondary stage, the individual
breaks out in a rash that does not itch;
hair loss and gray patches on the
mucous membranes in the mouth may
occur.
These symptoms soon disappear.
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In the terminal tertiary stage, gummas
(large destructive ulcers) may appear
on skin and within internal organs, and
the disease affects a wide variety of
organs.
In congenital syphilis, in which the
bacterium has crossed the placenta,
the child is born blind and/or with
anatomical malformations.
Antibiotics easily cure syphilis.
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Two Other Infections
Vaginitis is caused by a naturally
occurring yeast, Candida albicans, that
grows to infectious levels.
Trichomoniasis is an vaginal infection
caused by a flagellated protozoan.
The protozoan infection causes a white
or yellow foul-smelling discharge, while
the yeast causes a white, curdy
discharge accompanied by itching.
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Chapter Summary
The male reproductive system
continuously produces a large number
of sperm within a fluid medium.
The female reproductive system is
designed for the monthly production of
an egg and the preparation of the
uterus to house the developing fetus.
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Hormones control the monthly reproductive
cycle in females and play a significant
role in maintaining pregnancy when it
occurs.
Birth-control measures vary widely in
effectiveness.
Today, alternative methods of reproduction
include in vitro fertilization, artificial
insemination, and many others.
There are many serious sexually
transmitted diseases and some are of
epidemic proportions.
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