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Fetus and Parturition
Topics for today:
• Yolk sac and allantois• Hormone changes• Late embryo• Fetal development• The placenta• Parturition
Formation of yolk sac
Week 3-4
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Hormones and the placenta
Increased levels of
progesterone needed
for maintenance of
the placenta.
Increased levels of
progesterone needed
for maintenance of
the placenta.
Late embryo and placenta
Fetus and chorion
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Brainregion
Limbbuds
Jaws
Late embryo with limb buds
Eye
Heart
About 4 wks
About 8 wk
Early fetus with digits
Digits justbeginning toform
About 12 wk
Early fetus
Shows welldeveloped digits,jaw, and eye.
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About 14 wk
Mid-Late Fetus
About 16 wk About 26 wk
Structure of the placenta
Fetal/maternal exchange in placenta
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superior vena cava
foramen ovale
inferior vena cava
umbilical arteries
ductus arteriosus
ductus venosus
umbilical vein
placenta
Fetal circulation
Placenta is sitewhere fetal bloodis oxygenated
Blood blows thruforamen ovale,bypassing lungs
Blood blows thruforamen ovale,bypassing lungs
Origins ofreproductive
organs
mesonephric kidneyindifferent gonadmesonephric ductparamesonephric duct
cloaca
Closely tied todevelopment ofrenal organs
…derivatives ofurogenital ridge
Fetal Delivery
Placental stageExplusion stage
Dilation stageFull term fetus Oxytocin effects:
• uterine contractions
• explusion
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Topic for Friday:
Risk Factors for Disease and Mortality