The naturally occurring hormone erythropoietin is PRIMARILY produced by which of the following?
In addition to accounting for fluid, electrolyte, and acid-base homeostasis, the kidneys also provide neurohormonal activity such as erythropoietin (EPO) synthesis and vitamin D activation. EPO is a glycoprotein produced primarily by peritubular cells in the kidneys, with a small amount (10%) also produced in perisinusoidal cells of the liver (Figure). EPO stimulates the formation of red blood cells by increasing the number of erythroid precursors and accelerating the release of reticulocytes from the bone marrow. EPO production is stimulated by hypoxia and can be suppressed by polycythemia. Under normal circumstances, the body produces just enough EPO to maintain the red cell mass and replace senescent (old) and dying red cells. In patients with chronic kidney disease, the amount of EPO synthesized can be severely decreased, leading to anemia. There is also emerging evidence that...
