Vasa recta is absent or highly reduced in a

Options

A. juxtamedullary nephrons
B. cortical nephrons
C. both juxtamdullary and cortical nephrons
D. medullary nephrons

Answer

To solve the question regarding the absence or reduction of Vasa Recta in certain types of nephrons, let's break it down step by step.

### Step-by-Step Solution:

1. **Understanding Vasa Recta**:
- Vasa Recta are straight capillaries that supply blood to the renal medulla and are crucial for the concentration of urine. They play a significant role in maintaining the osmotic gradient in the kidney.

2. **Types of Nephrons**:
- There are two main types of nephrons in the kidney:
- **Cortical Nephrons**: These nephrons are primarily located in the renal cortex and have shorter loops of Henle.
- **Juxtamedullary Nephrons**: These nephrons are located near the medulla and have longer loops of Henle, which extend deep into the medulla.
- **Medullary Nephrons**: This term is often used interchangeably with juxtamedullary nephrons.

3. **Function of Nephrons**:
- **Cortical Nephrons**: They are primarily involved in the regulation of plasma volume and are not significantly involved in urine concentration.
- **Juxtamedullary Nephrons**: They are essential for concentrating urine due to their long loops of Henle and the presence of Vasa Recta.

4. **Presence of Vasa Recta**:
- Since cortical nephrons have shorter loops of Henle and are not involved in urine concentration, they either lack Vasa Recta or have them highly reduced.
- In contrast, juxtamedullary nephrons have well-developed Vasa Recta due to their role in urine concentration.

5. **Conclusion**:
- Based on the above information, the correct answer to the question "Vasa recta is absent or highly reduced in a" is **B. Cortical Nephrons**.

### Final Answer:
**B. Cortical Nephrons**