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Explain how the structure and functions of the placenta maintain pregnancy
- After an embryo implants in the uterine wall, tissues of the uterus and fetus form the placenta.
- The placenta has 2 major functions: 1) production of estrogen & progesterone, and 2) exchange of molecules between maternal & fetal blood.
- Progesterone and estrogen are needed to prevent menstruation and build up the wall of the uterus.
- The placenta begins to form when the fetus develops a villus, a finger-like growth into the uterus.
- The number of villi increases steadily to meet the needs of the growing fetus.
- Maternal blood flows out of capillaries into inter-villous spaces surrounding each villus.
- Fetal capillaries are very close to the surface of each villus (within 5 µm of the maternal blood).
- The cells separating fetal and maternal blood form a selectively permeable barrier known as the placental barrier.
- Microvilli project from each villus to increase surface area, which allows rapid diffusion of molecules.
- Nutrients and O2 diffuse from maternal blood to fetal blood, and carbon dioxide diffuses from fetal blood to maternal blood.
- Fetal blood flows toward the placenta in the umbilical artery, and away from the placenta in the umbilical vein.
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