The zygote undergoes rapid cell division over the first 30 hours after fertilization, dividing into 2, then 4, then 8 and 16 cells. The trophoblast layer develops into the chorion and amnion membranes, with the chorion growing finger-like villi to increase nutrient absorption and secreting HCG to sustain the corpus luteum, and the villi later forming part of the placenta. The amnion forms a sac around the fetus containing amniotic fluid to protect and provide room for movement of the fetus.

1. Cleavage of Zygote• Begins about 30 hrs after
fertilization
• Zygote divides first into 2
then 4 then 8 & 16 cells

2. TROPHOBLAST
• It is the outer layer of cells of blastocyst.
• It develops into two membranes:
chorion,
amnion.

3. The chorion
• It grows finger like
projections called
chorionic villi
• Increases surface area
for absorption of
nutrients
• Secretes HCG which
prevents degeneration
of corpus luteum
• Villi forms part of
placenta

4. The amnion
• Forms a sac around
fetus
• Encloses amniotic fluid
• Shock absorber
• Protect fetus from
damage
• Keeps skin moist
• Provides room for
movement
• Act as heat buffer