A substance not secreted by renal tubule

Options

A. Glucose
B. Para-aminohippuric acid
C. Ammonia
D. Potassium ions

Answer

To solve the question "A substance not secreted by renal tubule," we will analyze each option provided and determine which substance is not secreted by the renal tubules.

### Step-by-Step Solution:

1. **Understand the Function of Renal Tubules**:
- The renal tubules are responsible for the reabsorption and secretion of various substances during the process of urine formation.

2. **Evaluate the First Option: Glucose**:
- Glucose is primarily reabsorbed in the proximal convoluted tubule. Under normal physiological conditions, glucose is not secreted into the urine but is instead reabsorbed back into the bloodstream.
- **Conclusion**: Glucose is **not** secreted by renal tubules.

3. **Evaluate the Second Option: Para Amino Hippuric Acid (PAH)**:
- PAH is a substance that is actively secreted by the renal tubules. It is used to measure renal plasma flow and is not reabsorbed.
- **Conclusion**: PAH is **secreted** by renal tubules.

4. **Evaluate the Third Option: Ammonia**:
- Ammonia is produced during the metabolism of proteins and is secreted by the proximal tubule into the urine.
- **Conclusion**: Ammonia is **secreted** by renal tubules.

5. **Evaluate the Fourth Option: Potassium Ions**:
- Potassium ions are also actively secreted by the distal convoluted tubule and collecting duct, especially in response to aldosterone.
- **Conclusion**: Potassium ions are **secreted** by renal tubules.

6. **Final Conclusion**:
- Since glucose is the only substance listed that is not secreted by the renal tubules but rather reabsorbed, the correct answer to the question is **Glucose**.

### Final Answer:
**Glucose is the substance not secreted by the renal tubule.**

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