Route of tubular secretion is

Options

A. Blood `to` Interstitial fluid `to` Renal fluid
B. Renal fluid `to` Interstitial fluid `to` Blood
C. Blood `to` Renal fluid `to` Interstitial fluid
D. Interstitial fluid `to` Renal fluid `to` Blood

Answer

### Step-by-Step Solution:

1. **Understanding Tubular Secretion**:
- Tubular secretion is a process in the kidneys where substances such as metabolites and waste products are transferred from the blood into the urine. This process helps in the elimination of unwanted substances from the body.

**Hint**: Remember that tubular secretion is about moving waste products from the blood to the urine.

2. **Pathway of Tubular Secretion**:
- The pathway for tubular secretion begins with the blood. The unwanted metabolites are secreted from the blood into the interstitial fluid surrounding the nephron.

**Hint**: Think of the blood as the starting point for waste products that need to be eliminated.

3. **Role of Interstitial Fluid**:
- After the metabolites are secreted into the interstitial fluid, they are then transported into the renal tubules (nephrons) for further processing.

**Hint**: Interstitial fluid acts as a bridge between the blood and the renal tubules.

4. **Filtration in the Nephron**:
- Once in the nephron, the metabolites are filtered and then enter the renal fluid, which is part of the urine formation process.

**Hint**: The nephron is crucial for filtering and processing the waste products.

5. **Final Destination - Urine**:
- The final step is that the renal fluid, containing the filtered waste products, is eventually excreted as urine.

**Hint**: Remember that urine is the end product of the filtration and secretion processes in the kidneys.

### Conclusion:
The route of tubular secretion can be summarized as follows:
- Blood → Interstitial Fluid → Nephron (Renal Tubules) → Renal Fluid → Urine.

### Final Answer:
The correct route of tubular secretion is: Blood → Interstitial Fluid → Nephron → Renal Fluid → Urine.