Fertilization and development fertilization

1. Biology

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2. Fertilization

39–4 Fertilization and
Development
Fertilization
What is fertilization?
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3. Fertilization

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Development
Fertilization
The process of a sperm joining an egg is
called fertilization.
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4. Fertilization

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Fertilization
After the two haploid (N) nuclei fuse, a single diploid
(2N) nucleus is formed.
A diploid cell has a set of chromosomes from each
parent cell.
The fertilized egg is called a zygote.
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5. Early Development

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Early Development
Early Development
While still in the Fallopian tube, the zygote begins
to undergo mitosis.
Four days after fertilization, the embryo is a solid
ball of about 64 cells called a morula.
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6. Early Development

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Early Development
What are the stages of early development?
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7. Early Development

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Development
Early Development
The stages of early development include
implantation, gastrulation, and neurulation.
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8. Early Development

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Early Development
Implantation
As the morula grows, it becomes a hollow structure
with an inner cavity called a blastocyst.
6–7 days after fertilization, the blastocyst attaches
to the uterine wall.
The embryo secretes enzymes that digest a path
into it.
This process is known as implantation.
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9. Fertilization

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Fertilization
Fertilization and Implantation
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10. Early Development

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Early Development
Blastocyst cells specialize due to the activation of
genes.
This process, called differentiation, is responsible
for the development of the various types of tissue in
the body.
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11. Early Development

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Early Development
A cluster of cells, known as the inner cell mass,
develops within the inner cavity of the blastocyst.
The embryo will develop from these cells, while the
other cells will differentiate into tissues that surround
the embryo.
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12. Early Development

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Early Development
Gastrulation
The inner cell mass of the blastocyst gradually
sorts itself into two layers, which then give rise to a
third layer.
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13. Early Development

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Early Development
The third layer is produced by a process of cell
migration known as gastrulation.
Amniotic cavity
Primitive
streak
Mesoderm
Ectoderm
Endoderm
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14. Early Development

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Early Development
The result of gastrulation is the formation of three cell
layers—the ectoderm, the mesoderm, and the
endoderm.
Amniotic cavity
Primitive
streak
Mesoderm
Ectoderm
Endoderm
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15. Early Development

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Early Development
The ectoderm develops into the skin and nervous
system.
The endoderm forms the digestive lining and organs.
Mesoderm cells differentiate into internal tissues and
organs.
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16. Early Development

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Development
Early Development
Neurulation
Gastrulation is followed by neurulation.
Neurulation is the development of the nervous
system.
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17. Early Development

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Early Development
Shortly after gastrulation is complete, a block of
mesodermal tissue begins to differentiate into the
notochord.
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18. Early Development

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Early Development
As the notochord develops, the neural groove
changes shape, producing neural folds.
Neural crest
Neural fold
Notochord
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19. Early Development

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Early Development
Gradually, these folds move together to create a
neural tube from which the spinal cord and the
nervous system develop.
Neural crest
Neural tube
Ectoderm
Notochord
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20. Early Development

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Early Development
Extraembryonic Membranes
As the embryo develops, membranes form to
protect and nourish the embryo.
Two of these membranes are the amnion and the
chorion.
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21. Early Development

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Early Development
Amniotic sac
The amnion
develops into a
fluid-filled
amniotic sac,
which cushions
and protects the
developing
embryo.
Placenta
Umbilical cord
Uterus
Amnion
Fetus
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22. Early Development

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Early Development
Fingerlike projections called chorionic villi form on the
outer surface of the chorion and extend into the
Maternal portion
uterine lining.
Fetal portion
of placenta
of placenta
Chorionic villus
Amnion
Umbilical cord
Maternal
artery
Umbilical
arteries
Umbilical
vein
Maternal
vein
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23. Early Development

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Early Development
The chorionic villi and uterine lining form the placenta.
The placenta connects the mother and developing
embryo.
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24. Early Development

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Early Development
What is the function of the placenta?
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25. Early Development

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Development
Early Development
The placenta is the embryo's organ of
respiration, nourishment, and excretion.
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26. Early Development

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Early Development
The placenta acts as a barrier to some harmful or
disease-causing agents.
Some disease causing agents, such as German
measles and HIV can cross the placenta.
Some drugs, including alcohol and medications also
can penetrate the placenta and affect development.
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27. Early Development

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Early Development
After eight weeks, the embryo is called a
fetus.
After three months, most major organs and
tissues are formed. During this time, the
umbilical cord also forms.
The umbilical cord connects the fetus to the
placenta.
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28. Control of Development

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Control of Development
Control of Development
The fates of many cells in the early embryo are not
fixed.
The inner cell mass contains embryonic stem cells,
unspecialized cells that can differentiate into nearly
any specialized cell type.
Researchers are still learning the mechanisms that
control stem cell differentiation.
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29. Later Development

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Later Development
Later Development
4–6 months after fertilization:
• The heart can be heard with a stethoscope.
• Bone replaces cartilage that forms the early
skeleton.
• A layer of soft hair grows over the fetus’s skin.
• The fetus grows and the mother can feel it
moving.
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30. Later Development

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Later Development
During the last three months, the organ systems
mature.
• The fetus doubles in mass.
• It can now regulate its body temperature.
• The central nervous system and lungs
completely develop.
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31. Childbirth

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Childbirth
Childbirth
About nine months after fertilization, the fetus is
ready for birth.
A complex set of factors affects the onset of
childbirth.
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32. Childbirth

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Childbirth
The mother’s posterior pituitary gland releases the
hormone oxytocin, which affects involuntary muscles
in the uterine wall.
These muscles begin rhythmic contractions known as
labor.
The contractions become more frequent and more
powerful.
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33. Childbirth

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Development
Childbirth
The opening of the cervix expands until it is large
enough for the head of the baby to pass through it.
At some point, the amniotic sac breaks, and the fluid
it contains rushes out of the vagina.
Contractions force the baby out through the vagina.
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34. Childbirth

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Development
Childbirth
The baby now begins an independent existence.
Its systems quickly adapt to life outside the uterus,
supplying its own oxygen, excreting waste on its own,
and maintaining its own body temperature.
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35. Multiple Births

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Multiple Births
Multiple Births
If two eggs are released during the same cycle and
fertilized by two different sperm, fraternal twins
result.
A single zygote may split apart to produce two
embryos, which are called identical twins.
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36. Early Years

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Early Years
Early Years
The first two years of life are called infancy. It is a
period of rapid growth and development.
Childhood lasts from infancy until puberty.
Adolescence begins with puberty and ends with
adulthood.
Puberty produces a growth spurt that will conclude
in mid-adolescence.
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37. Adulthood

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Adulthood
Adulthood
Development continues during adulthood.
Adults reach their highest levels of physical
strength and development between the ages of 25
and 35.
Most people begin to show signs of aging in their
30s.
Around age 65, most body systems become less
efficient, making homeostasis more difficult to
maintain.
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38. 39–4

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39. 39–4

Fertilization takes place in the
a. ovary.
b. Fallopian tube.
c. cavity of the uterus.
d. cervix.
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40. 39–4

The process in which a blastocyst attaches to
the wall of the uterus is called
a. fertilization.
b. implantation.
c. gastrulation.
d. neurulation.
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41. 39–4

The central nervous system develops during
which phase of early development?
a. gastrulation
b. neurulation
c. implantation
d. fertilization
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42. 39–4

The placenta is a structure that
a. belongs entirely to the mother.
b. belongs entirely to the fetus.
c. brings blood from the mother and fetus close
together.
d. provides an impermeable barrier between
the mother and the fetus.
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43. 39–4

Which of the following is not a primary germ
layer?
a. neural tube
b. endoderm
c. ectoderm
d. mesoderm
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