The "erythropoietin" hormone regulates :

Options

A. Blood pressure
B. Water level of blood
C. Glucose level of blood
D. Rate of formation of red blood cells

Answer

**Step-by-Step Solution:**

1. **Understanding Erythropoietin**: Erythropoietin (EPO) is a hormone that plays a crucial role in the regulation of red blood cell production in the body.

2. **Source of Erythropoietin**: This hormone is produced by the juxtaglomerular cells located in the kidneys.

3. **Function of Erythropoietin**: The primary function of erythropoietin is to stimulate erythropoiesis, which is the process of red blood cell formation. When oxygen levels in the blood are low, the kidneys release more erythropoietin to increase the production of red blood cells, thereby enhancing the oxygen-carrying capacity of the blood.

4. **Exclusion of Other Options**:
- Blood pressure regulation is primarily managed by hormones such as ANF (Atrial Natriuretic Factor) and others, not erythropoietin.
- The water level in the blood is regulated by hormones like aldosterone and antidiuretic hormone (ADH).
- Blood glucose levels are controlled by insulin and glucagon, which are secreted by the pancreas.

5. **Conclusion**: Therefore, the correct answer to the question is that erythropoietin regulates the rate of formation of red blood cells.

**Final Answer**: Erythropoietin regulates the rate of formation of red blood cells.

---