Identify the correct statement regarding urine formation

Options

A. Countercurrent mechanism works around the PCT and glomerulus.
B. To prevent diuresis, ADH facilitates water reabsorption from the latter parts of the tubule.
C. Maximum reabsorption of electrolytes occurs in the Henley's loop.
D. A decrease in blood pressure can increase the GFR

Answer

To identify the correct statement regarding urine formation, we can analyze each of the provided statements step by step.

### Step-by-Step Solution:

1. **Understanding the Countercurrent Mechanism**:
- The first statement claims that the countercurrent mechanism works around the PCT (Proximal Convoluted Tubule) and the glomerulus.
- However, the countercurrent mechanism primarily occurs in the loop of Henle, which is located in the renal medulla, not in the PCT or glomerulus.
- Therefore, this statement is **incorrect**.

2. **Role of ADH in Water Reabsorption**:
- The second statement mentions that to prevent diuresis, ADH (Antidiuretic Hormone) facilitates water reabsorption from the latter parts of the tubule.
- ADH is indeed secreted by the posterior pituitary gland and acts on the distal convoluted tubule (DCT) and collecting ducts to promote water reabsorption, especially when blood volume or blood pressure decreases.
- This statement is **correct**.

3. **Reabsorption of Electrolytes**:
- The third statement asserts that maximum reabsorption of electrolytes occurs in Henle's loop.
- In reality, approximately 70-80% of electrolytes and water are reabsorbed in the PCT, not in the loop of Henle.
- Thus, this statement is **incorrect**.

4. **Effect of Blood Pressure on GFR**:
- The fourth statement states that a decrease in blood pressure can increase the GFR (Glomerular Filtration Rate).
- This is not true; a decrease in blood pressure typically results in a decrease in GFR because the pressure in the glomerular capillaries is essential for filtration.
- Therefore, this statement is also **incorrect**.

### Conclusion:
After evaluating all the statements, the only correct statement regarding urine formation is **the second statement**: "To prevent diuresis, ADH facilitates water reabsorption from the latter parts of the tubule."