Renal portal system is absent in

Options

A. Reptiles
B. Amphibians
C. Reptiles and Amphibians
D. mammals

Answer

### Step-by-Step Solution:

1. **Understanding the Renal Portal System**:
The renal portal system is a network of veins that carries blood from the hind limbs and tail to the kidneys before it returns to the heart. This system is present in some vertebrates.

2. **Identifying Groups with Renal Portal System**:
- **Amphibians**: In amphibians, such as frogs, blood is collected from various veins (femoral, sciatic, pelvic, and external iliac veins) and transported to the kidneys via the renal portal vein. This indicates that amphibians have a renal portal system.
- **Reptiles**: Reptiles also possess a renal portal system. The blood from the posterior part of the body travels through the kidneys before returning to the heart, indicating the presence of this system.

3. **Examining Mammals**:
- In mammals, the heart is structured with four chambers, which allows for the complete separation of oxygenated and deoxygenated blood. This anatomical feature means that mammals do not require a renal portal system, as their circulatory system is efficient enough to manage blood flow without it.

4. **Conclusion**:
Based on the above analysis, the renal portal system is absent in mammals. Therefore, the correct answer to the question is **mammals**.

### Final Answer:
The renal portal system is absent in **mammals**.

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