End Show Slide 1 of 47 Warm-Up #19 Answer questions #1-6 on Text 1024 Section Assessment. Answer in...
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End Show Slide 1 of 47 Warm-Up #19 Answer questions #1-6 on Text 1024 Section Assessment. Answer in complete sentences. Copyright Pearson Prentice Hall
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Transcript of End Show Slide 1 of 47 Warm-Up #19 Answer questions #1-6 on Text 1024 Section Assessment. Answer in...
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Warm-Up #19
Answer questions #1-6 on Text 1024 Section Assessment. Answer in complete sentences.
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39–4 Fertilization and Development
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Objectives
1. Describe fertilization
2. Identify the stages of early development
3. Describe the function of the placenta
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Fertilization
•The process of a sperm joining an egg is called fertilization.
•It occurs in the oviduct.
•If an egg is fertilized, a zygote forms and begins to undergo cleavage, also known as cell division (mitosis), as it travels to the uterus.
•As each cell divides, the number of cells doubles. Four days after fertilization, the embryo is a solid ball of about 64 cells called a morula.
•As the morula grows, a cavity forms in the center—this hollow structure is called a blasotcyst.
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39–4 Fertilization and Development
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Fertilization
??
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Early Development
The stages of early development include implantation, gastrulation, and neurulation.
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Implantation
•About six or seven days after fertilization, the blastocyst attaches itself to the wall of the uterus.
•The embryo secretes enzymes that digest a path into the soft tissue.
•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.
•Differentiation is the specialization of cells to develop into specific tissues and structures.
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39–4 Fertilization and Development
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Blastocyst Formation
The First Two Weeks
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Early Development
Implantation & Differentiation
Implantation
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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.
Early Gastrulation
Amniotic cavity
Primitive streak
Ectoderm
Endoderm
Mesoderm
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Early Development
3 Germ Layers
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 the development of the nervous system.
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39–4 Fertilization and Development
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Neural crest Neural fold
Notochord
Early Development
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39–4 Fertilization and Development
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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.
Nova - Gastrulation
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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 Placenta
The placenta is the connection between the mother and the developing embryo or fetus.
It is through the placenta that the embryo gets its oxygen and nutrients and excretes its waste products.
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The Placental Barrier
•The placenta acts as a barrier to some harmful or disease-causing agents.
•Other disease-causing agents can penetrate the placenta and affect development—AIDS and German measles, for example.
•Drugs, including alcohol, medications and other addictive substances cause also cross the placenta and cause damage to the developing fetus.
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Early Development
Fetal Development (after 8+ weeks).
After three months (the first trimester), most major organs and tissues are formed. During this time, the umbilical cord also forms.
The umbilical cord connects the fetus to the placenta.
Placenta & Fetal Development
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Later Development
Later Development
4–6 months after fertilization (the second trimester):
• 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 third trimester), 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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SUMMARY
What is fertilization?
What is a morula?
What is a blastocyst?
What are the early stages of development?
What are the three germ layers?
What are the extraembryonic tissues?
What is the function of the placenta?
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Study Guide page 60.
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Homework
STUDY FOR TEST
Homework Packets
Warm-Ups #18-20
Study Guide
Extra Credit Article
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