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