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Chapter 21 Growth and Development

PRENATAL PERIOD Prenatal period begins at conception and continues until birth (about 39 weeks) Science of fetal growth and development called embryology Slide 3

PRENATAL PERIOD Fertilization to implantation requires about 10 days Fertilization normally occurs in outer third of oviduct (Figure 21-2) Fertilized ovum called a zygote; zygote is genetically complete—all that is needed for expression of hereditary traits is time and nourishment After 3 days of cell division, the zygote has developed into a solid cell mass called a morula Continued cell divisions of the morula produce a hollow ball of cells called a blastocyst Blastocyst implants in the uterine wall about 10 days after fertilization Blastocyst forms the amniotic cavity and chorion of the placenta (Figure 21-4) Placenta provides for exchange of nutrients between the mother and fetus Slide 4

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PRENATAL PERIOD Periods of development Length of pregnancy, or gestation period, is about 39 weeks Embryonic phase extends from the third week after fertilization to the end of week 8 of gestation Fetal phase extends from week 8 to week 39 of gestation All organ systems are formed and functioning by month 4 of gestation (Figure 21-6) Slide 7

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