Assertion: Vasa recta is absent or highly reduced in cortical nephrons.
Reason: Cortical nephrons are mainly concerned with concentration of urine.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. if both assertion and reason are true but reason is not the correct explanation of assertion.
C. if assertion is true but reason is false
D. if both assertion and reason are false.

Explanation

To analyze the assertion and reason provided in the question, we can break it down step by step:

### Step 1: Understanding the Assertion
The assertion states that "Vasa recta is absent or highly reduced in cortical nephrons."
- Cortical nephrons are primarily located in the renal cortex of the kidneys.
- They have a shorter loop of Henle compared to juxtamedullary nephrons, which extend deeper into the medulla.
- Vasa recta, which are straight capillaries that supply blood to the nephron, are indeed either absent or significantly reduced in cortical nephrons.

### Step 2: Understanding the Reason
The reason states that "Cortical nephrons are mainly concerned with the concentration of urine."
- While cortical nephrons do play a role in urine formation, they are not primarily responsible for the concentration of urine.
- The concentration of urine is mainly the function of juxtamedullary nephrons, which have longer loops of Henle that extend deeper into the medulla, allowing for greater concentration due to the counter-current multiplier system.

### Step 3: Conclusion
- The assertion is **true**: Vasa recta is indeed absent or highly reduced in cortical nephrons.
- The reason is **false**: Cortical nephrons are not mainly concerned with the concentration of urine; this is primarily the role of juxtamedullary nephrons.

### Final Answer
The assertion is true, but the reason is false.

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