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Understanding Human Development: From Fertilization to Birth

This chapter explores differentiation, stages of development, prenatal periods, fertilization, placental role, genetics inheritance, embryonic and fetal periods, implantation, germ layers, and extraembryonic membranes in human development. Detailed explanations and visual aids provide a comprehensive overview of the intricate processes involved.

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Understanding Human Development: From Fertilization to Birth

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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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