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Fetal Development
Prenatal period3 stages
• Cleavage = Fertilization to 2nd week
• Embryonic stage = end of 2nd week through 8th week
• Fetal stage = 9th week through birth
Trophoblast secretes hCG to maintain corpus luteum
Fig. 23-10
Multi-part development model
6. Early blastocyst (yellow = inner cell mass)
7. Mid blastocyst (yellow = ectoderm, orange = endoderm)
8. Late blastocyst with implantation
9. Inner cell mass
10. Trophoblast
4 part Embryonic Development Model
Upper right model (Blastocyst)
Inner cell mass= at pointer
Purple slit = amnion
Yellow = preliminary yolk sac
34 = trophoblast
34
Upper left model(Embryo)
42 = Connecting stalk (at pointer)
40 = amniotic cavity
38 = Yolk sac
42
40
38
Upper left model(Embryo)
Chorionic villi = at pointer 46
Embryonic disc – between amnion & yolk sac
46
48 = Chorion
Lower Right Model
49 = umbilical cord
38 = yolk sac
49
38
48
47
47 = Amnion
Lower Left Model
47
49
51
47 = amnion
49 = Umbilical cord
50 = Large chorionic villa (Fetal placenta)
51 = Chorion (entire structure fused with amnion)
50