Chapter 7 Power point – Prenatal Development Stages of Prenatal Development Neonatal Adaptations.
Prenatal Development
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Transcript of Prenatal Development
![Page 1: Prenatal Development](https://reader036.fdocuments.in/reader036/viewer/2022062514/557dc390d8b42a63048b49f9/html5/thumbnails/1.jpg)
The Stages of Prenatal Development
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• Induction– During prenatal development differences in
cytoplasmic composition trigger changes in genetic activity
• Gestation periods– Three trimesters
Embryonic and Fetal Periods
![Page 3: Prenatal Development](https://reader036.fdocuments.in/reader036/viewer/2022062514/557dc390d8b42a63048b49f9/html5/thumbnails/3.jpg)
SECTION 29-4 The First Trimester
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• Cleavage – Zygote becomes a preembryo then a blastocyst
• Implantation – Blastocyst burrows into uterine endometrium
• Placentation – Blood vessels form around blastocyst and placenta develops
• Embryogenesis – Formation of a viable embryo
The First Trimester
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• A series of cell divisions that subdivides the cytoplasm of the zygote– Trophoblast – outer layer of cells – Inner cell mass – cluster of cells at one end of
blastocyst
Cleavage and blastocyst formation
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Figure 29.2
Cleavage and Blastocyst Formation
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• Occurs about 7 days after fertilization• Trophoblast enlarges and spreads
– Maternal blood flows through open lacunae
• Gastrulation– Embryonic disc composed of germ layers
• Endoderm• Mesoderm• Ectoderm
Implantation
![Page 8: Prenatal Development](https://reader036.fdocuments.in/reader036/viewer/2022062514/557dc390d8b42a63048b49f9/html5/thumbnails/8.jpg)
Stages in Implantation
Figure 29.3
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Figure 29.4
The Inner Cell Mass and Gastrulation
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• Gastrulation – By day 12 surface cells move toward the
primitive streak – A third germ layer forms
• The three germ layers are:– Ectoderm – superficial cells that did not migrate– Endoderm – cells facing the blastocoele– Mesoderm – migrating cells between ectoderm
and endoderm
Germ layers
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• Four extraembryonic membranes:– Yolk sac – Amnion– Allantois– Chorion
Extraembryonic Membranes
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Figure 29.5a, b
Extraembryonic Membranes and Placenta Formation
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Figure 29.5c, d
Extraembryonic Membranes and Placenta Formation
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Figure 29.5e
Extraembryonic Membranes and Placenta Formation
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• Yolk sac– Important site of blood cell formation
• Amnion– Encloses fluid that surrounds and cushions
developing embryo
• Allantois– Eventually becomes bladder
• Chorion
Embryo Anatomy