Which of the following hormones is not secreted by the kidneys?

Options

A. Erythropoietin
B. Renin
C. Rennin
D. Calcitriol

Answer

To determine which hormone is not secreted by the kidneys, we need to analyze the options provided: erythropoietin, renin, and calcitriol.

### Step-by-Step Solution:

1. **Identify Hormones Secreted by the Kidneys**:
- The kidneys are known to secrete several important hormones. The primary hormones include:
- **Erythropoietin**: This hormone stimulates the production of red blood cells in the bone marrow.
- **Renin**: This enzyme plays a crucial role in regulating blood pressure and fluid balance in the body.
- **Calcitriol**: This is the active form of Vitamin D, which helps regulate calcium and phosphorus levels in the body.

2. **Analyze Each Option**:
- **Erythropoietin**: Secreted by the kidneys, it is involved in red blood cell production.
- **Renin**: Although often referred to in discussions about hormones, renin is actually an enzyme that initiates the renin-angiotensin-aldosterone system (RAAS) for blood pressure regulation.
- **Calcitriol**: This hormone is also secreted by the kidneys and is important for calcium regulation.

3. **Identify the Incorrect Option**:
- Among the options, **renin** is the only one that is not a hormone but rather an enzyme. The confusion may arise from its role in hormonal pathways, but it does not fit the definition of a hormone itself.

4. **Conclusion**:
- Therefore, the hormone that is **not secreted by the kidneys** is **renin**.

### Final Answer:
**Renin** is the correct answer as it is an enzyme, not a hormone.