A student has read that hematopoiesis occurring in the wall of the yolk sac declines after the eighth week of gestation and asks the instructor for clarification. What statement by the faculty member is most accurate?
A.
"All of the blood needed is transported across the placenta."
B.
"Bone marrow production of blood begins in week 8."
C.
"The fetal liver takes over that function then."
D.
"You must have misread that information."
ANS: C
Formation and development of red blood cells (hematopoiesis) occurs in the wall of the yolk sac beginning in the third week. The function gradually declines after the eighth gestational week when the fetal liver begins to take over this process.
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