Erythropoietin (EPO) is made primarily by the __________.

• A. pancreas
• B. spleen
• C. pituitary gland
• D. kidneys

Answer: (D)

Verified step by step guidance

1. Understand the role of erythropoietin (EPO): EPO is a hormone that stimulates the production of red blood cells in the bone marrow.
2. Identify the primary site of EPO production: EPO is primarily produced by the kidneys in response to low oxygen levels in the blood.
3. Consider the function of the kidneys: The kidneys monitor oxygen levels and release EPO to increase red blood cell production when needed.
4. Review the other options: The pancreas, spleen, and pituitary gland have different primary functions unrelated to EPO production.
5. Conclude that the kidneys are the correct answer based on their role in monitoring blood oxygen levels and producing EPO.