Implantation 4 Flashcards
Explain how the placenta can maintain extensive fetal growth in the third trimester despite only a relatively small increase in placental size.
1
Q
What happens to the placenta in the third trimester?
A
Weight will increase from about 300 grams at 28-30 weeks gestation to about 500 grams at term
2
Q
How does the placenta provide adequate nutrition and gas exchange when the fetal mass is effectively outgrowing the placental mass in the third trimester of pregnancy?
A
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Increased branching of the secondary and tertiary villi into smaller terminal villi at term
- effectively increases surface area of the villi in contact with the maternal blood without having to increase overall placental mass
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Within the terminal villi, fetal capillaries are essentially directly subadjacent to the syncytiotrophoblast layer
- decreases diffusion distance
3
Q
How will the placenta respond if the fetus experiences chronic hypoxia/ischemia in utero prior to term?
A
-
Villi will become smaller sooner
- tries to increase surface area
- leads to improper growth of the placenta
- referred to as hypermature villi, distal villous hypoplasia, or Tenney-Parker change
- Local ischemic/hypoxic change in the placenta results in clumping of the syncytiotrophoblast nuclei into “knots”