Urine becomes more and more hypertonic as it passes through

Options

A. descending limb of loop of Henle
B. proximal convoluted tubule
C. ascending limb of loop of Henle
D. distal convoluted tubule

Answer

To answer the question "Urine becomes more and more hypertonic as it passes through," we need to analyze the structure and function of the nephron, specifically focusing on the parts of the nephron involved in urine concentration.

### Step-by-Step Solution:

1. **Understanding the Nephron Structure**:
- The nephron is the functional unit of the kidney and consists of several parts: the renal corpuscle (which includes Bowman's capsule and glomerulus), proximal convoluted tubule (PCT), loop of Henle (which has descending and ascending limbs), distal convoluted tubule (DCT), and collecting duct.

2. **Role of the Proximal Convoluted Tubule (PCT)**:
- In the PCT, ultrafiltration occurs, where blood plasma is filtered, and essential substances like sodium ions and bicarbonate ions are reabsorbed. However, this part does not significantly contribute to urine hypertonicity.

3. **Function of the Loop of Henle**:
- The loop of Henle consists of two limbs: the descending limb and the ascending limb.
- The descending limb is highly permeable to water but not to solutes. As urine passes through this limb, water is reabsorbed into the surrounding medullary interstitium, leading to an increase in the concentration of solutes in the urine, making it hypertonic.

4. **Ascending Limb of the Loop of Henle**:
- The ascending limb is impermeable to water but actively transports sodium and chloride ions out of the urine. This process dilutes the urine, making it less concentrated as it ascends.

5. **Conclusion**:
- As urine travels through the descending limb of the loop of Henle, water is reabsorbed, leading to increased solute concentration and hypertonicity. Therefore, the correct answer to the question is that urine becomes more hypertonic as it passes through the **descending limb of the loop of Henle**.

### Final Answer:
- The correct answer is **the descending limb of the loop of Henle**.

---