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Gabbe’s Obstetrics Essentials Normal and Problem Pregnancies Ebook PDF

Gabbe’s Obstetrics Essentials Normal and Problem Pregnancies Ebook PDF

Gabbe’s Obstetrics Essentials Normal and Problem Pregnancies Ebook PDF

Gabbe’s Obstetrics Essentials Normal and Problem Pregnancies Ebook PDF The mature human placenta is a discoid organ that consists of an elaborately branched fetal villous tree bathed directly by maternal blood of the villous hemochorial type. Normal term placental weight averages 450 g and represents approximately one seventh (one sixth with cord and membranes) of the fetal
weight.

• Continual development throughout pregnancy leads to progressive enlargement of the surface area for exchange (12 to 14 m2 at term) and reduction in the mean diffusion distance between the maternal and fetal circulations (approximately 5 to
6 μm at term).

• The maternal circulation to the placenta is not fully established until the end of the first trimester; hence organogenesis takes place in a low-oxygen environment of approximately 20 mm Hg, which may protect against free radicalmediated teratogenesis.

• The exocoelomic cavity acts as an important reservoir of nutrients during early pregnancy, and the secondary yolk sac is important in the uptake of nutrients and their transfer to the fetus.

• Oxygen is a powerful mediator of trophoblast proliferation and
invasion, villous remodeling, and placental angiogenesis.

• Ensuring an adequate maternal blood supply to the placenta during the second and third trimesters is an essential aspect of placentation and is dependent upon physiologic conversion of the spiral arteries induced by invasion of the endometrium by extravillous trophoblast during early pregnancy. Many complications of pregnancy, such as preeclampsia, appear to be secondary to deficient invasion.

• All transport across the placenta must take place across the syncytial covering of the villous tree, syncytiotrophoblast, the villous matrix, and the fetal endothelium, each of which may impose its own restriction and selectivity. Exchange will occur via one of four basic processes: (1) bulk flow/solvent drag, (2) diffusion, (3) transporter-mediated mechanisms, and (4) endocytosis/exocytosis.

Uterine blood flow at term averages 750 mL/min, or 10% to15% of maternal cardiac output.

Gabbe’s Obstetrics Essentials Normal and Problem Pregnancies Ebook PDF

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