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Chapter 8 Genetics, Conception, and Fetal Development Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. Conception Cell division Gametogenesis Mitosis Meiosis Spermatogenesis Orogenesis Conception Ovum Sperm Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 2 Fig. 8-5. Gametogenesis and fertilization. A, Oogenesis. Gametogenesis in the female produces one mature ovum and three polar bodies. Note relative difference in overall size between ovum and sperm. B, Spermatogenesis. Gametogenesis in the male produces four mature gametes, the sperm. C, Fertilization results in the single-cell zygote and restoration of the diploid number of chromosomes. Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 3 Conception—cont’d Fertilization Morula Blastocyst Implantation Chorionic villi Decidua basalis Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 4 Embryo and Fetus Primary germ layers Ectoderm Mesoderm Endoderm Development of the embryo Membranes Chorion Amnion and amniotic cavity Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 5 Embryo and Fetus—cont’d Amniotic fluid Yolk sac Umbilical cord Placenta Structure Functions Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 6 Fig. 8-8. A, First weeks of human development. Follicular development in ovary, ovulation, fertilization, and transport of early embryo down uterine tube and into uterus, where implantation occurs. Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 7 Fig. 8-8. B, Blastocyst embedded in endometrium. Germ layers forming. Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 8 Fig. 8-9. Development of fetal membranes. Note gradual obliteration of intrauterine cavity as decidua capsularis and decidua vera meet. Also note thinning of uterine wall. Chorionic and amnionic membranes are in apposition to each other but may be peeled apart. Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 9 Fig. 8-11. Schematic drawing of placenta illustrating how it supplies oxygen and nutrition to embryo and removes its waste products. Deoxygenated blood leaves fetus through umbilical arteries and enters placenta, where it is oxygenated. Oxygenated blood leaves placenta through umbilical vein, which enters fetus via the umbilical cord. Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 10 Embryo and Fetus—cont’d Fetal maturation Viability • Capability of fetus to survive outside uterus • Limitations based on central nervous system function and oxygenation capability of lungs Respiratory system • Primary surfactants Fetal circulatory system Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 11 Fig. 8-12. Schematic illustration of fetal circulation. The colors indicate the oxygen saturation of the blood, and the arrows show the course of the blood from the placenta to the heart. The organs are not drawn to scale. Observe that three shunts permit most of the blood to bypass the liver and lungs: (1) ductus venosus, (2) foramen ovale, and (3) ductus arteriosus. The poorly oxygenated blood returns to the placenta for oxygen and nutrients through the umbilical arteries. Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 12 Embryo and Fetus—cont’d Fetal maturation Hematopoietic system Gastrointestinal system Renal system Neurologic system • Sensory awareness Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 13 Embryo and Fetus—cont’d Fetal maturation Musculoskeletal system Integumentary system Immunologic system Endocrine system Reproductive system Mosby items and derived items © 2010, 2006, 2002 by Mosby, Inc., an affiliate of Elsevier Inc. 14