Final answer:
The regulation of red blood cell production is mainly controlled by tissue hypoxia, which stimulates the secretion of erythropoietin (EPO) from the kidneys to increase RBC synthesis in the bone marrow.
Step-by-step explanation:
The regulation of red blood cell (RBC) production is primarily controlled by the physiological factor of tissue hypoxia. When the body experiences low oxygen levels, it compensates by producing erythropoietin, or EPO, a hormone that stimulates the formation of RBCs. The kidney plays a crucial role by producing 85 percent of circulating EPO, which in turn increases erythrocyte production in the bone marrow. Conditions such as anemia are a result of inadequate RBC or hemoglobin levels, leading to reduced oxygen delivery to tissues, causing fatigue, lethargy, and increased risk for infection. On the contrary, an elevated level of hemoglobin or excess RBCs, a condition known as polycythemia, can increase the blood’s viscosity, making it harder for the heart to pump blood effectively.