The 'Hormone Erythropoietin' (EPO), which stimulates the production of red blood cells in the bone marrow, is primarily secreted by the: MCQ with Answer and Explanation

Erythropoietin (EPO) is a glycoprotein hormone that is the primary regulator of red blood cell production (erythropoiesis). It is primarily produced and secreted by the interstitial fibroblasts in the kidneys (specifically in the peritubular capillary bed) in response to cellular hypoxia (low oxygen levels). A small amount is also produced by the liver. EPO travels to the bone marrow, where it stimulates the proliferation and differentiation of erythroid progenitor cells into mature red blood cells.