Fetal Development

Prenatal period 3 stages Cleavage = Fertilization to 2 nd week Embryonic stage = end of 2 nd week through 8 th week Fetal stage = 9 th week through birth

Trophoblast secretes hCG to maintain corpus luteum

Fig

Multi-part development model

1.Zygote 2. 2 cell stage 3. 4 cell stage 4. 8 cell stage 5. Morula (12-16 cells)

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

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 = Amnion

Lower Left Model = amnion 49 = Umbilical cord 50 = Large chorionic villa (Fetal placenta) 51 = Chorion (entire structure fused with amnion) 50