Assertion: The Henle's loop and vasa recta play a significant role in producing a concentrated urine.
Reason: The counter current arrangement of Henle's loop and vasa recta helps in this.

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

**Step-by-Step Solution:**

1. **Understanding the Assertion**: The assertion states that the Henle's loop and vasa recta play a significant role in producing concentrated urine. This is true because the nephron, particularly the loop of Henle and the vasa recta, is crucial for urine concentration.

2. **Understanding the Reason**: The reason provided is that the countercurrent arrangement of the Henle's loop and vasa recta helps in this process. The countercurrent mechanism refers to the flow of fluids in opposite directions, which enhances the concentration gradient necessary for water reabsorption.

3. **Role of the Loop of Henle**: The loop of Henle consists of a descending limb and an ascending limb. The descending limb is permeable to water but not to salts, allowing water to be reabsorbed into the surrounding tissue, thus concentrating the filtrate.

4. **Role of Vasa Recta**: The vasa recta are capillaries that run parallel to the loop of Henle. They also have a countercurrent arrangement, which means they absorb the water that is reabsorbed from the loop of Henle, maintaining the osmotic gradient necessary for further water reabsorption.

5. **Countercurrent Mechanism**: As the filtrate moves down the descending limb, it becomes more concentrated due to water loss. When it moves up the ascending limb, salts are reabsorbed while water remains in the filtrate. The countercurrent arrangement of the vasa recta allows for efficient exchange of substances, ensuring that the osmolarity of the medulla is maintained, which is essential for producing concentrated urine.

6. **Conclusion**: Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the answer is that both the assertion and reason are true, and the reason is the correct explanation for the assertion.

**Final Answer**: A) Both assertion and reason are true, and reason is the correct explanation for the assertion.

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