Final answer:
Physiological anemia refers to a decrease in red blood cell (RBC) levels during pregnancy as a normal adaptation to support increased blood volume. The dilution effect of expanded plasma volume reduces RBC concentration, but the total RBC mass remains relatively constant or increases.
Step-by-step explanation:
Physiological anemia refers to a decrease in red blood cell (RBC) levels that occurs during pregnancy. This is a normal adaptation to support the increased blood volume needed by both the mother and the developing fetus. The decrease in RBC levels is due to the dilution effect of the expanded plasma volume, resulting in lower RBC concentration in the blood. However, the total RBC mass remains relatively constant or even increases during pregnancy to ensure adequate oxygen delivery to the tissues.