Read the following statements about the excretory system in humans:
I. A fall in GFR can activate the JG cells to release renin.
II. ADH can also affect the kidney function by its constrictory effects on blood vessels.
III. The proximity between the Henle's loop and vasa recta, as well as the counter-current in them help in maintaining an increasing osmolarity towards the outer medullary interstitium.
IV Our lungs remove large amounts of `CO_(2)` (108 litres/day).
V. Renal calculi are the stone or insoluble mass of crystallised salts like oxalates within the kidney.
How many of these are correct?

Options

A. None
B. One
C. Two
D. Three

Answer

To determine how many statements about the excretory system in humans are correct, we will evaluate each statement one by one.

### Step-by-Step Solution:

1. **Statement I**: "A fall in GFR can activate the JG cells to release renin."
- **Evaluation**: This statement is true. The juxtaglomerular (JG) cells in the kidneys respond to a decrease in the glomerular filtration rate (GFR) by releasing renin. Renin plays a crucial role in regulating blood pressure and fluid balance.

2. **Statement II**: "ADH can also affect the kidney function by its constrictory effects on blood vessels."
- **Evaluation**: This statement is also true. Antidiuretic hormone (ADH), also known as vasopressin, primarily promotes water reabsorption in the kidneys but can also cause vasoconstriction, which helps maintain blood pressure.

3. **Statement III**: "The proximity between the Henle's loop and vasa recta, as well as the counter-current in them help in maintaining an increasing osmolarity towards the outer medullary interstitium."
- **Evaluation**: This statement is false. The counter-current mechanism between the Henle's loop and the vasa recta actually helps maintain an increasing osmolarity towards the inner medullary interstitium, not the outer medulla.

4. **Statement IV**: "Our lungs remove large amounts of CO₂ (108 liters/day)."
- **Evaluation**: This statement is false. The lungs remove approximately 500 liters of CO₂ per day, not 108 liters.

5. **Statement V**: "Renal calculi are the stone or insoluble mass of crystallised salts like oxalates within the kidney."
- **Evaluation**: This statement is true. Renal calculi, commonly known as kidney stones, can form from crystallized salts such as calcium oxalate.

### Summary of Evaluations:
- **Correct Statements**: I, II, V (3 statements)
- **Incorrect Statements**: III, IV (2 statements)

### Final Answer:
**Three statements are correct.**

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