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Chapter 29, part 1

Chapter 29, part 1. Development and Inheritance. Learning Objectives. Explain the relationship between differentiation and development and specify the various stages of development Describe the process of fertilization

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Chapter 29, part 1

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  1. Chapter 29, part 1 Development and Inheritance

  2. Learning Objectives • Explain the relationship between differentiation and development and specify the various stages of development • Describe the process of fertilization • List the three prenatal periods and describe the major events associated with each • Discuss the importance of the placenta as an endocrine organ

  3. Learning Objectives • Discuss the structural and functional changes in the uterus during gestation • List and discuss the events that occur during labor and delivery • Relate basic principles of genetics to the inheritance of human traits

  4. SECTION 29-1An Overview of Topics in Development

  5. Differentiation and development • Development • Gradual modification of physical and physiological characteristics • Differentiation • The creation of different types of cells

  6. Stages of development • Prenatal development • Embryological • Changes occurring the first two months after fertilization • Fetal • Begins at the start of the ninth week and continues until birth • Postnatal development • Commences at birth and continues to maturity

  7. SECTION 29-2Fertilization

  8. Fertilization (conception) • Occurs in the uterine tubes • Within a day of ovulation • Spermatozoa cannot fertilize an ovum until after capacitation

  9. Figure 29.1 Fertilization Figure 29.1a

  10. Figure 29.1 Fertilization Figure 29.1b

  11. The Oocyte at Ovulation • Oocyte is in meiosis II • Surrounded by the corona radiate • Spermatozoa release hyaluronidase and acrosin • Enzymes required to penetrate corona radiate • Single spermatozoan contacts oocyte, fertilization begins • Oocyte activation PLAY Animation: Fertilization and Oocyte Activation

  12. Oocyte activation • Oocyte completes meiosis II • Functionally mature ovum • Female pronucleus and male pronucleus fuse (amphimixis) • Polyspermy prevented by membrane depolarization and cortical reaction

  13. SECTION 29-3The Stages of Prenatal Development

  14. Embryonic and Fetal Periods • Induction • During prenatal development differences in cytoplasmic composition trigger changes in genetic activity • Gestation periods • Three trimesters

  15. SECTION 29-4The First Trimester

  16. The First Trimester • 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

  17. Cleavage and blastocyst formation • 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

  18. Figure 29.2 Cleavage and Blastocyst Formation Figure 29.2

  19. Implantation • 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

  20. Figure 29.3 Stages in Implantation PLAY Animation: Location of the Endometrium Figure 29.3

  21. Figure 29.4 The Inner Cell Mass and Gastrulation Figure 29.4

  22. Germ layers • 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

  23. Extraembryonic Membranes • Four extraembryonic membranes: • Yolk sac • Amnion • Allantois • Chorion

  24. Figure 29.5 Extraembryonic Membranes and Placenta Formation Figure 29.5a, b

  25. Figure 29.5 Extraembryonic Membranes and Placenta Formation Figure 29.5c, d

  26. Figure 29.5 Extraembryonic Membranes and Placenta Formation Figure 29.5e

  27. Embryo Anatomy • Yolk sac • Important site of blood cell formation • Amnion • Encloses fluid that surrounds and cushions developing embryo • Allantois • Eventually becomes bladder • Chorion

  28. Figure 29.6 A Three-Dimensional View of Placental Structure Figure 29.6a

  29. Placentation • Chorionic villi extend into maternal tissue • Forms intricate branching network for maternal blood • Umbilical cord connects fetus to placenta

  30. Hormones of the placenta • Trophoblast secretes hormones to maintain pregnancy • HCG • Estrogens • Progesterone • hPL • Placental prolactin • relaxin

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