The final step in blood volume regulation is production of erythrocytes. Erythropoietin is a hormone released by the kidneys that causes bone marrow to increase production of red blood cells, raising the total mass of circulating red cells. The stimuli for erythropoietin release include hy-poxia and reduced hematocrit. An increase in circulating AVP and aldosterone enhances salt and water retention and results in an elevated plasma volume. The increased plasma volume (with a constant volume of red blood cells) results in a lower hematocrit. The decrease in hematocrit stimulates erythropoietin release, which stimulates red blood cell synthesis and, therefore, balances the increase in plasma volume with a larger red blood cell mass.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.