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REPRODUCTION AND
DEVELOPMENT
Chapter Outline
IMPACTS/ISSUES: MIND-BOGGLING Contraception
BIRTHS Abortion
HOW ANIMALS REPRODUCE AND Assisted Reproduction
DEVELOP Overview of Sexually Transmitted Disease
Asexual Reproduction Common STDs
Sexual Reproduction HUMAN PRENATAL DEVELOPMENT
Variations on Sexual Reproduction Cleavage and Implantation
Stages in Reproduction and Development Embryonic Development
THE HUMAN REPRODUCTIVE SYSTEM Fetal Development
Male Reproductive System Functions of the Placenta
How Sperm Form Maternal Effects on Prenatal Development
Female Reproductive System FROM BIRTH ONWARD
Egg Formation and the Ovarian Cycle The Process of Birth
Hormones and the Menstrual Cycle Nourishing the Newborn
Menstruation-Related Disorders Postnatal Development
HOW PREGNANCY HAPPENS IMPACTS/ISSUES REVISITED
Sexual Intercourse SUMMARY
Fertilization SELF-QUIZ
FERTILITY AND REPRODUCTIVE HEALTH CRITICAL THINKING
Objectives
• Identify the developmental processes common to all animals.
• Recount the story of human reproduction from a single fertilized egg cell to a multicellular
organism with trillions of specialized cells.
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2. • Identify and discuss the six stages of reproduction and development that occur in animals that
have tissues and organs.
• Describe the major components and functions of the male and female reproductive system.
• Describe the development of male and female sexual gametes (sperm and egg).
• Describe the ovarian cycle with its related hormonal changes.
• Recognize the most common menstruation-related disorders.
• Describe the various methods of contraception for both men and women.
• Describe the symptoms and consequences of the most common sexually transmitted diseases.
• Identify and describe the structures and functions related to human pre-natal development.
• Describe possible complications to pre-natal development due to diseases and maternal behavior
patterns.
• Describe the normal development of a mother and baby.
Key Terms
asexual reproduction ovary menstrual cycle
hermaphrodite prostate gland menstruation
parthenogenesis scrotum contraception
sexual reproduction semen orgasm
blastula seminal vesicles ovum
cleavage testes in vitro fertilization
differentiation vas deferens sexually transmitted disease
ectoderm cervix amnion
endoderm corpus luteum blastocyst
fertilization oocyte chorion
gastrula oviduct human chorionic
gastrulation ovulation gonadotropin (HCG)
mesoderm uterus placenta
yolk vagina fetus
zygote erection labor
ejaculation menopause
Lecture Outline
26.1 Impacts/Issues: Mind-Boggling Births:
A. Over the past two decades, the number of multiple births has increased by almost 60 percent.
B. There are also nearly four times as many higher order multiple births (triplets or more).
C. The number of first-time mothers more than forty years old doubled in the past decade.
D. While a woman’s fertility peaks in her mid-twenties, by the age of thirty-nine, her chance of
conceiving naturally has declined by about half.
1. Many of these women require fertility drugs to become pregnant, and these drugs raise the
likelihood of multiple births.
26.2 How Animals Reproduce and Develop
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3. A. Asexual reproduction
1. Some animals reproduce asexually, producing offspring identical to one another and to
their parents.
a. Most animals reproduce sexually, and so produce genetically variable offspring.
2. Gene combinations that make the parent successful can be expected to do the same for
offspring.
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4. B. Sexual reproduction
1. In sexually reproducing animals, gametes combine and form a zygote.
2. Cleavage (mitotic divisions) produces a blastula.
a. This hollow ball of cells undergoes gastrulation, resulting in the production of a
three-layered gastrula.
b. All organs of the body can be traced to these three layers.
c. Cells of the gastrula differentiate to form specialized tissues.
3. Cell divisions, migrations, shape changes, and programmed cell death shape organs and
give rise to the final body form.
C. Variations on sexual reproduction
1. While most animals reproduce sexually and have separate sexes, some are hermaphrodites
that produce both eggs and sperm.
2. With external fertilization, gametes are released into water.
a. Most animals on land have internal fertilization.
b. Gametes meet in a female’s body.
26.3 The Human Reproductive System
A. A male’s testes produce sperm and secrete the sex hormone testosterone.
B. Sperm and secretions from accessory glands form semen.
1. Semen is propelled through a series of ducts and leaves the body through an opening in the
penis.
C. A woman’s ovaries make eggs and secrete sex hormones (estrogens and progesterone).
1. Oviducts connect the ovaries to the uterus, where offspring develop.
2. The vagina is the organ of intercourse and also the birth canal.
D. In men, germ cells divide continually to produce sperm.
E. By contrast, a woman is born with all the immature eggs she will ever have.
1. From puberty until menopause, a woman’s eggs mature—one at a time—in an
approximate monthly cycle.
2. During each ovarian cycle, the uterine lining thickens in preparation for pregnancy.
3. If pregnancy does not occur, the woman sheds the uterine lining (menstruates), and the
cycle begins again.
26.4 How Pregnancy Happens
A. In preparation for intercourse, a male’s penis becomes inflated by the inflow of blood, and a
female’s reproductive tract becomes lubricated with mucus.
B. During orgasm, smooth muscles of the reproductive tract undergo rhythmic contractions.
1. In males, ejaculation forces sperm out of the penis.
C. Fertilization usually occurs in the oviduct.
1. Usually an oocyte changes after one sperm penetrates it, preventing other sperm from
binding.
2. The result of fertilization is a zygote, the first cell of the new individual.
26.5 Fertility and Reproductive Health
A. There are a wide variety of contraceptive methods, and Table 26.1 gives examples of these.
B. Abortions may be spontaneous or induced.
C. For those who cannot conceive naturally, in vitro fertilization is another option.
1. By this process, an egg and sperm are combined outside the body.
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5. 2. The process was first carried out in 1978.
D. There is a vast range of sexually transmitted diseases (STDs).
1. Each year, about 15 million Americans are infected with various pathogens (Table 26.2).
2. Two-thirds of those infected are under age twenty-five; one-quarter are teenagers.
3. More than 65 million Americans (1 in 5) have a viral STD that cannot be cured.
26.6 Human Prenatal Development
A. Cleavage and implantation
1. Cleavage produces a blastocyst, which implants in the uterus.
a. Projections from its surface invade maternal tissue and form a placenta.
B. Embryonic development
1. The placenta permits exchanges between a mother and embryo without intermingling
bloodstreams.
a. Pathogens and toxins, as well as nutrients, can cross the placenta.
2. Gastrulation occurs about two weeks after fertilization and produces a three-layered
embryo.
3. Chordate features such as a neural tube, notochord, and pharyngeal arches form later in
the embryonic period.
C. Fetal development
1. The fetal period begins at the end of the eighth week.
2. Heartbeats are detected at about five months, and limb movements are felt at five to six
months.
3. Lungs are not fully formed until about 28 weeks (7 months), so births before this point are
highly risky.
4. A fetus born before 22 weeks will not survive.
5. Hormonal changes prepare a woman’s body for labor and nursing.
6. During labor, hormone-stimulated contraction of uterine smooth muscle forces the fetus
out of the body.
7. Milk secreted by mammary glands provides nutrition and also has antibodies that protect
the newborn from infection.
a. Some pathogens and toxins can be transmitted in breast milk.
D. Functions of the placenta
1. All exchange of materials between an embryo and its mother takes place by way of the
placenta.
a. The maternal and embryonic bloodstreams never mix.
2. Substances move between maternal and embryonic blood by diffusing across the walls of
the embryonic vessels in the chorionic villi.
3. Oxygen and nutrients diffuse from pooled maternal blood into embryonic vessels in the
villi.
a. Wastes diffuse the other way, and the mother’s body disposes of them.
4. The placenta also has a hormonal role.
E. Maternal effects on prenatal development
1. An embryo or fetus depends on its mother to supply nutrients.
a. It is also exposed to pathogens and toxins that enter the mother’s body.
2. Diseases, alcohol, drugs, and behavior can significantly increase the probability of birth
defects and/or death of the fetus.
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6. 26.7 From Birth Onward
A. Hormonal changes prepare a woman’s body for labor and nursing.
B. During labor, hormone-stimulated contraction of uterine smooth muscle forces the fetus out of
the body.
C. Milk secreted by mammary glands provides nutrition and also has antibodies that protect the
newborn from infection.
1. Some pathogens and toxins can be transmitted in breast milk.
D. Growth and development continues after birth.
1. Bones are not fully mature until early adulthood.
26.8 Issues/Impacts Revisited: Mind-Boggling Births
A. A high level of FHS increases the likelihood of multiple births.
B. A genetic connection is clear since a woman who is a fraternal twin has a doubled chance of
giving birth to fraternal twins.
C. Significant differences exist as a result of ethnicity; fraternal twins are most common among
women of African descent, while rare among Asians.
D. Bearing children later in life tends to increase the incidence of fraternal twinning as a result of
natural increases in FHS production.
E. FSH level does not influence formation of identical twins.
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