Final answer:
In response to severe anemia when the bone marrow can't produce enough red blood cells, the body increases the production of erythropoietin (EPO) which stimulates the bone marrow to produce more RBCs.
Step-by-step explanation:
When a patient has severe anemia and the bone marrow is unable to effectively produce red blood cells to meet the increased demand, one of the body's responses is to increase production of the hormone erythropoietin (EPO). This hormone, primarily produced by the kidneys, stimulates the bone marrow to produce more oxygen-carrying red blood cells. Conditions such as aplastic anemia, sickle cell anemia, and iron or vitamin deficiency anemia all result from faulty or decreased RBC production. In the face of such anemic conditions, when the kidneys sense that the oxygen levels are too low, they respond by elevating EPO production to attempt to normalize the RBC count. However, if the bone marrow is compromised, as in aplastic anemia or due to replacement by cancer cells, the response may not be sufficient, leading to persistent anemia.