Download Fetal Development

Chapter 8
Genetics, Conception,
and Fetal Development
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Conception
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Cell division
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Gametogenesis
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Mitosis
Meiosis
Spermatogenesis
Orogenesis
Conception
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Ovum
Sperm
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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.
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Conception—cont’d
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Fertilization
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Morula
Blastocyst
Implantation
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Chorionic villi
Decidua basalis
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Embryo and Fetus
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Primary germ layers
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Ectoderm
Mesoderm
Endoderm
Development of the embryo
Membranes
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Chorion
Amnion and amniotic cavity
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Embryo and Fetus—cont’d
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Amniotic fluid
Yolk sac
Umbilical cord
Placenta
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Structure
Functions
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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.
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Fig. 8-8. B, Blastocyst embedded in endometrium. Germ layers forming.
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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.
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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.
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Embryo and Fetus—cont’d
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Fetal maturation
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Viability
• Capability of fetus to survive outside uterus
• Limitations based on central nervous system
function and oxygenation capability of lungs
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Respiratory system
• Primary surfactants
Fetal circulatory system
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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.
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Embryo and Fetus—cont’d
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Fetal maturation
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Hematopoietic system
Gastrointestinal system
Renal system
Neurologic system
• Sensory awareness
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Embryo and Fetus—cont’d
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Fetal maturation
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Musculoskeletal system
Integumentary system
Immunologic system
Endocrine system
Reproductive system
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