5. Which of the following statements about erythropoietin is true? 1. It facilitates the proliferation and differentiation of the erythrocyte lineage. 2. It is a hormone produced by the thyroid gland. 3. It is a hemopoietic growth factor that prompts lymphoid stem cells to leave the bone marrow. 4. Both a and b are true

The correct answer is 1. It facilitates the proliferation and differentiation of the erythrocyte lineage.<br /><br />Erythropoietin (EPO) is a hormone produced primarily by the kidneys in response to low oxygen levels in the blood. It plays a crucial role in stimulating the production of red blood cells (erythrocytes) in the bone marrow. EPO binds to erythropoietin receptors on the surface of erythroid progenitor cells, promoting their proliferation and differentiation into mature red blood cells.<br /><br />Option 2 is incorrect because erythropoietin is not produced by the thyroid gland. It is mainly produced by the kidneys.<br /><br />Option 3 is incorrect because erythropoietin does not prompt lymphoid stem cells to leave the bone marrow. Lymphoid stem cells give rise to lymphocytes, which are part of the immune system, and are not directly influenced by erythropoietin.<br /><br />Option 4 is incorrect because both statements 1 and 2 are not true. Only statement 1 is true.