End Show Slide 1 of 47 Biology Mr. Karns Development Fertilization.
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End Show Slide 1 of 47 Biology Mr. Karns Developmen t Fertilizat ion
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Transcript of End Show Slide 1 of 47 Biology Mr. Karns Development Fertilization.
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Biology Mr. Karns
DevelopmentFertilization
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39–4 Fertilization and Development
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When an egg is fertilized, human development begins.
In this process, a single cell undergoes a series of cell divisions that results in the formation of a new human being.
Development
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Fertilization
Fertilization
During sexual intercourse, sperm are released when semen is ejaculated through the penis into the vagina.
Sperm swim through the uterus into the Fallopian tubes.
if an egg is present in one of the Fallopian tubes, its chances of being fertilized are good.
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Fertilization
The egg is surrounded by a protective layer that contains binding sites to which sperm can attach.
When a sperm attaches to a binding site, its head releases enzymes that break down the protective layer of the egg.
The sperm nucleus enters the egg, and chromosomes from the sperm and egg are brought together.
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What is fertilization?
Fertilization
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Fertilization
The process of a sperm joining an egg is called 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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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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Early Development
What are the stages of early development?
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Early Development
The stages of early development include implantation, gastrulation, and neurulation.
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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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39–4 Fertilization and Development
Fertilization
Fertilization and Implantation
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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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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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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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Mesoderm
Amniotic cavity
Primitive streak
Ectoderm
Endoderm
Early Development
The third layer is produced by a process of cell migration known as gastrulation.
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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
Ectoderm
Endoderm
Mesoderm
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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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Early Development
Neurulation
Gastrulation is followed by neurulation.
Neurulation is the development of the nervous system.
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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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Neural crest Neural fold
Notochord
Early Development
As the notochord develops, the neural groove changes shape, producing neural folds.
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Neural crest Neural tube
Ectoderm
Notochord
Early Development
Gradually, these folds move together to create a neural tube from which the spinal cord and the nervous system develop.
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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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Early Development
The amnion develops into a fluid-filled amniotic sac, which cushions and protects the developing embryo.
Uterus
Amnion
Fetus
Amniotic sac
Placenta
Umbilical cord
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Fingerlike projections called chorionic villi form on the outer surface of the chorion and extend into the uterine lining.
Early Development
Fetal portion of placenta
Maternal portion of placenta
Maternal artery
Maternal vein
Umbilical vein
Umbilical arteries
Umbilical cord
Amnion
Chorionic villus
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The chorionic villi and uterine lining form the placenta.
The placenta connects the mother and developing embryo.
Early Development
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Early Development
What is the function of the placenta?
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Early Development
The placenta is the embryo's organ of respiration, nourishment, and excretion.
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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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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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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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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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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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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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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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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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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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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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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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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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39–4
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39–4
Fertilization takes place in the
a. ovary.
b. Fallopian tube.
c. cavity of the uterus.
d. cervix.
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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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The central nervous system develops during which phase of early development?
a. gastrulation
b. neurulation
c. implantation
d. fertilization
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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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39–4
Which of the following is not a primary germ layer?
a. neural tube
b. endoderm
c. ectoderm
d. mesoderm
END OF SECTION
