Y

1 Hematocrit

J Plasma Oncotic Pressure

f Plasma Volume

FIGURE 10 Summary of cardiovascular and renal changes in pregnancy. ERPF, effective renal plasma flow; GFR, glomerular filtration rate.

infusions. Thus, as already described for renin and AVP, control mechanisms that govern ANF secretion respond normally to acute changes in volume but defend vascular volume at a higher set point.

Figure 10 summarizes the cardiovascular and renal changes produced in the first trimester and continued throughout gestation. Hormonal signals arising in the tro-phoblast and/or the ovary and acting directly on vascular smooth muscle and the osmoreceptors initiate the series of changes that ultimately increase placental perfusion. It is likely, but not established, that these peripheral effects are reinforced by complementary effects on regulatory centers in the brain. The adaptive value of most of these changes appears to reside in ensuring adequacy of uteroplacental perfusion while maintaining sufficient circulatory reserve to service the needs of the mother. The adaptive value of the increase in GFR is unknown, but it may facilitate excretion of fetal wastes and dietary toxins.

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