Chapter 18
Reproduction and Development
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Section 1 Human Reproduction
Section 2 Growth and Development
Concept Map
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Chapter 18
Section 1 Human Reproduction
Bellringer
Use the words below to answer the questions that
follow.
together
alone
sperm
eggs
1. What is one difference between the male and
female reproductive systems?
2. What is one thing the male and female reproductive
systems have in common?
Write your answers in your Science Journal.
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Chapter 18
Section 1 Human Reproduction
What You Will Learn
• The testes and penis are two structures of the male
reproductive system.
• The ovaries, uterus, and vagina are three structures of
the female reproductive system.
• Sperm are produced in the testes. Eggs are produced
in the ovaries.
• During fertilization, each parent contributes one
chromosome from each of his or her chromosome
pairs to an offspring.
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Chapter 18
Section 1 Human Reproduction
The Male Reproductive System
• The function of the male reproductive system is to
make and deliver sperm to the female reproductive
system.
• The testes are a pair of organs that hang outside the
body in the scrotum. The testes make sperm and the
male sex hormone testosterone.
• Testosterone regulates sperm production and the
development of male characteristics.
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Chapter 18
Section 1 Human Reproduction
The Male Reproductive System, continued
• Sperm made in a testis mature in the epididymis.
Mature sperm leave the epididymis through another
tube, the vas deferens.
• Before the sperm leave the body, they mix with fluids
from several glands, including the prostate gland.
• This mixture of sperm and fluids is semen.
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Chapter 18
Section 1 Human Reproduction
The Male Reproductive System, continued
• Semen passes through the vas deferens into the
urethra, the tube that runs from the bladder through
the penis.
• The penis is the external organ through which semen
exits a male’s body and can enter a female’s body.
• Most of the sperm that leave the body exit during
ejaculation.
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Chapter 18
Section 1 Human Reproduction
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Chapter 18
Section 1 Human Reproduction
The Male Reproductive System, continued
• Some sperm may exit the penis before ejaculation
without the male’s awareness.
• Sexual activity that releases any sperm--even a few-can lead to fertilization and pregnancy.
• Fertilization occurs when a sperm penetrates an egg.
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Chapter 18
Section 1 Human Reproduction
The Female Reproductive System
• The female reproductive system produces eggs. When an egg
is fertilized, the female reproductive system nourishes the
developing embryo and gives birth.
• The two ovaries are the organs that make eggs.
• Ovaries also release estrogen and progesterone, the main
female sex hormones.
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Chapter 18
Section 1 Human Reproduction
The Female Reproductive System, continued
• The female sex hormones regulate the release of
eggs and the development of female characteristics.
• An egg is released during ovulation, and it passes
into a fallopian tube, or oviduct.
• Fertilization usually takes place in a fallopian tube,
which leads to the uterus.
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Chapter 18
Section 1 Human Reproduction
The Female Reproductive System, continued
• The tiny embryo enters the uterus and may become
embedded in the lining of the uterus.
• The uterus is the muscular organ in which an
embryo develops into a baby.
• During birth, the baby passes through the vagina.
The vagina is the canal between the outside of the
body and the uterus.
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Chapter 18
Section 1 Human Reproduction
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Chapter 18
Section 1 Human Reproduction
The Female Reproductive System, continued
• Menstrual Cycle To prepare the body for pregnancy,
a woman’s reproductive system goes through the
monthly menstrual cycle.
• The first day of the cycle begins with menstruation,
the monthly discharge of blood and tissue from the
lining of the uterus.
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Chapter 18
Section 1 Human Reproduction
The Female Reproductive System, continued
• Menstruation lasts about 5 days. The lining of the
uterus begins to thicken again at the end of
menstruation.
• Ovulation occurs on about the 14th day of the cycle.
Before ovulation, an egg develops within a follicle in
the ovary.
• If the released egg is not fertilized, menstruation
begins again, flushing the egg away. The cycle
typically lasts 28 days.
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Chapter 18
Reproduction and Development
Menstrual Cycle and Uterine Lining
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Visual Concept
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Chapter 18
Section 1 Human Reproduction
Fertilization
• Fertilization may occur when sperm are present in
the female reproductive system within a few days of
ovulation.
• Fertilization occurs when a single sperm penetrates
the egg. The fertilized egg is called a zygote.
• The sperm and egg each have only one copy of each
chromosome.
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Chapter 18
Section 1 Human Reproduction
Fertilization, continued
• After fertilization, the zygote has two copies of each
chromosome, one from each parent.
• Recall that chromosomes contain genes, which are
the inherited information for making proteins.
• These genes are found in all of your body’s cells.
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Section 1 Human Reproduction
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Chapter 18
Section 1 Human Reproduction
Multiple Births
• In a multiple birth, a mother gives birth to two or more babies at
a time. Twins are the most common multiple birth.
• Identical twins occur when the fertilized egg splits in two.
Fraternal twins occur from two different eggs.
• Fraternal twins are more common than identical twins, and can
be of opposite sexes.
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Chapter 18
Section 1 Human Reproduction
Reproductive System Problems
• Sexually Transmitted Diseases A sexually transmitted
disease (STD) can pass from one person to another person
during sexual contact.
• AIDS, or acquired immune deficiency syndrome, is a fatal STD.
It is caused by the HIV virus, which destroys the body’s immune
system.
• Gonorrhea, Chlamydia, and genital herpes are STDs affecting
millions of Americans each year.
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Chapter 18
Reproduction and Development
AIDS (Acquired Immunodeficiency
Syndrome)
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Chapter 18
Section 1 Human Reproduction
Reproductive System Problems, continued
• Cancer Cancer is a disease in which cells grow at
an uncontrolled rate. Cancer can occur in
reproductive organs.
• Cancer of the testes and cancer of the prostate gland
are the most common reproductive system cancers in
men.
• Breast cancer and cancer of the cervix are the most
common reproductive cancers in women.
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Chapter 18
Section 1 Human Reproduction
Reproductive System Problems, continued
• The cervix is the lower part of the uterus, which
opens to the vagina.
• Infertility STDs and cancers are two causes
infertility. An infertile couple is unable to have
children.
• Men who do not produce enough healthy sperm may
be infertile. Women who do not ovulate normally may
be infertile.
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Chapter 18
Section 1 Human Reproduction
Reproductive System Problems, continued
• In the United States, about 15% of married couples
have difficulty producing offspring.
• Many of these couples are infertile.
• Assisted reproductive technology, or ART, helps
some infertile couples give birth.
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Chapter 18
Section 2 Growth and Development
Bellringer
Name the stages of physical development you have
passed through in your life thus far.
Write your answers in your Science Journal.
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Chapter 18
Section 2 Growth and Development
What You Will Learn
• Fertilization is the beginning of an embryo’s
development during pregnancy.
• Organs and tissues develop as an embryo becomes
a fetus.
• A developing human relies on the placenta and
umbilical cord.
• There are many stages of human development from
birth to death.
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Chapter 18
Section 2 Growth and Development
From Fertilization to Embryo
• Human development usually begins with sexual
activity, during which a man ejaculates millions of
sperm into a woman’s vagina.
• A few hundred sperm may travel from the vagina,
through the uterus, and into a fallopian tube.
• If an egg is present, the sperm cover its protective
outer coating until one sperm penetrates the coating.
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Chapter 18
Section 2 Growth and Development
From Fertilization to Embryo, continued
• Only one sperm can enter the egg, as the coating
changes to prevent any other sperm from entering.
• The nucleus of the sperm joins with the nucleus of
the egg, and the egg is fertilized.
• The fertilized egg, or zygote, undergoes many cell
divisions as it travels down the fallopian tube to the
uterus.
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Chapter 18
Section 2 Growth and Development
From Fertilization to Embryo, continued
• The fertilized egg or zygote is also known as an
embryo until the 10th week of pregnancy.
• By seven or eight days after fertilization, the embryo
is a tiny ball of cells and ready for implantation.
• Implantation is the embedding of the embryo in the
thick, nutrient-rich lining of the uterus.
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Section 2 Growth and Development
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Chapter 18
Section 2 Growth and Development
From Embryo to Fetus
• After implantation, the placenta forms. The placenta
is a two-way exchange organ between the mother
and developing embryo.
• Oxygen and nutrients pass from the mother to the
embryo through the blood vessels of the placenta.
• Wastes from the embryo move into the mother’s
blood through the placenta.
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Chapter 18
Reproduction and Development
Pregnancy Overview
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Chapter 18
Section 2 Growth and Development
From Embryo to Fetus, continued
• The blood of the embryo and mother do not mix, but
do share materials.
• Weeks 1 and 2 Doctors usually consider
pregnancy as starting from the first day of a
woman’s last menstrual period.
• Although fertilization has not yet taken place, it is an
easy date from which to count. Pregnancy lasts about
40 weeks from that day.
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Chapter 18
Section 2 Growth and Development
From Embryo to Fetus, continued
• Weeks 3 and 4 In week 3, the zygote moves to the
uterus. After the first cell division, the zygote is called
an embryo.
• The embryo divides many times to become a ball of
cells that implants itself in the wall of the uterus.
• Some cells differentiate, or specialize to become
blood cells and other cell types.
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Chapter 18
Section 2 Growth and Development
From Embryo to Fetus, continued
• Weeks 5 to 8 From this stage until birth, the embryo
is surrounded by a thin membrane called the amnion.
• Amniotic fluid fills the amnion, which cushions and
protects the embryo.
• In week 5, the umbilical cord forms. The umbilical
cord connects the embryo to the placenta.
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Chapter 18
Section 2 Growth and Development
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Chapter 18
Section 2 Growth and Development
From Embryo to Fetus, continued
• In this stage, the heart, brain and other organs start
to form and grow.
• In weeks 5 and 6, tiny eyes, ears, spinal cord, and
limb buds appear. In week 8, muscles start to
develop
• By week 8, the 16 mm long embryo can swallow and
blink.
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Chapter 18
Section 2 Growth and Development
From Embryo to Fetus, continued
• Weeks 9 to 16 Cells continue to form tissues and
organs. By week 9, the embryo may make tiny
movements.
• After week 10, the embryo is called a fetus. At week
13, the fetus’s face begins to look more human.
• The fetus grows rapidly at this time, from 36 mm at
week 10 to 108-116 mm at week 16.
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Chapter 18
Section 2 Growth and Development
From Embryo to Fetus, continued
• Weeks 17 to 24 The fetus usually begins to make
movements that the mother can feel by week 18.
• During this time, the fetus has reached a length of 25
to 30 cm. It can hear sounds and may react to loud
noises.
• A fetus born at 24 weeks might survive if given
intensive medical care.
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Chapter 18
Section 2 Growth and Development
From Embryo to Fetus, continued
• Weeks 25 to 36 The fetus continues to receive
oxygen through the placenta, but has well developed
lungs now.
• By 32 weeks, the fetus’s eyes open and close and
respond to light. Some scientists believe the fetus
can even dream at this stage.
• At 36 weeks, the fetus is almost ready to be born.
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Chapter 18
Section 2 Growth and Development
Birth
• A full-term pregnancy usually lasts about 40 weeks,
but a fetus is considered fully developed at 38 weeks.
• As birth begins, the mother’s uterus begins a series
of muscular contractions called labor.
• Usually, these contractions push the fetus out
through the vagina until the baby is born.
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Chapter 18
Section 2 Growth and Development
Birth, continued
• The newborn is still connected to the placenta by the
umbilical cord.
• The cord is tied and cut. The site of connection is
marked by the navel for the rest of the baby’s life.
• Shortly after birth, the mother expels the placenta,
and labor is complete.
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Chapter 18
Section 2 Growth and Development
From Birth to Death
• Infancy and Childhood After birth, the human body
continues to go through several stages of
development.
• Infancy lasts from birth to age 2. Growth is very rapid
during this stage.
• Coordination improves as the nervous system and
muscles develop. Baby teeth appear.
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Chapter 18
Section 2 Growth and Development
From Birth to Death, continued
• Childhood lasts from age 2 to puberty. Growth
continues to be very fast during this stage.
• Permanent teeth replace baby teeth. Nerve pathways
and muscle coordination increase.
• Complex skills are now learnable, such as the ability
to ride a bike.
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Chapter 18
Section 2 Growth and Development
From Birth to Death, continued
• Adolescence Adolescence lasts from puberty to the
beginning of adulthood. During puberty, a person’s
reproductive system matures.
• In most boys, puberty occurs between the ages of 11
and 16.
• During this time, a male’s body becomes more
muscular. His voice deepens, and body and facial
hair appear.
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Chapter 18
Section 2 Growth and Development
From Birth to Death, continued
• In most girls, puberty occurs between the ages of 9
and 14.
• During this time, the amount of fat in the hips and
thighs increases, the breasts enlarge, body hair
appears, and menstruation begins.
• Adulthood Adulthood can be divided into stages as
well. From age 20 to 40 is considered young
adulthood.
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Chapter 18
Section 2 Growth and Development
From Birth to Death, continued
• During young adulthood, physical development is at
its peak.
• Signs of aging typically begin around age 30.
• Early signs of aging include loss of muscle flexibility,
deterioration of eyesight, increase in body fat, and
some hair loss.
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Chapter 18
Section 2 Growth and Development
From Birth to Death, continued
• From age 40 to 65 is considered middle age. During
this time, hair may gray, athletic ability declines, and
skin may wrinkle.
• Individuals more than 65 are considered older adults.
• Although the aging process continues through the
end of life, many older adults lead very active lives.
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Chapter 18
Reproduction and Development
Concept Map
Use the terms below to complete the concept map
on the next slide.
fertilization
an embryo
zygote
egg
sperm
a fetus
uterus
implantation
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Chapter 18
Reproduction and Development
Concept Map
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Chapter 18
Reproduction and Development
Concept Map
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