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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