When does glomerular filtration occurs in Bowman's capsule?

Options

A. When hydrostatic pressure of blood in the glomerulus is 70 mmHg and net filtrate pressure is - 25 mmHg
B. When hydrostatic pressure of blood in the glomerulus is 70 mmHg and net filtrate pressure is - 35 mmHg
C. When hydrostatic pressure of blood in the glomerulus is 75 mmHg and net filtrate pressure is 25 mmHg
D. When hydrostatic pressure of blood in the glomerulus is 70 mmHg and net filtrate pressure is - 70 mmHg

Answer

To determine when glomerular filtration occurs in Bowman's capsule, we need to understand the relationship between hydrostatic pressure and net filtration pressure.

### Step-by-Step Solution:

1. **Understanding Glomerular Filtration**:
- Glomerular filtration is the process by which blood is filtered in the kidneys, specifically in the glomerulus, to form urine. This process occurs in Bowman's capsule.

2. **Key Pressures Involved**:
- **Hydrostatic Pressure in the Glomerulus (HPg)**: This is the pressure exerted by the blood within the glomerular capillaries. It drives the filtration process.
- **Hydrostatic Pressure in Bowman's Capsule (HPc)**: This is the opposing pressure exerted by the fluid in Bowman's capsule.
- **Osmotic Pressure (OP)**: This is the pressure exerted by proteins in the blood that draws water back into the capillaries, opposing filtration.

3. **Net Filtration Pressure (NFP)**:
- The net filtration pressure is calculated using the formula:
\[ NFP = HPg - (HPc + OP) \]
- For filtration to occur, the net filtration pressure must be positive.

4. **Analyzing the Options**:
- We need to find a scenario where the hydrostatic pressure in the glomerulus is sufficient to overcome both the hydrostatic pressure in Bowman's capsule and the osmotic pressure.
- The options provided are:
1. HPg = 70 mm, NFP = 25 mm
2. HPg = 70 mm, NFP = 35 mm
3. HPg = 75 mm, NFP = 25 mm
4. HPg = 70 mm, NFP = 70 mm

5. **Evaluating Each Option**:
- Option 1: Not sufficient for filtration (NFP < 0).
- Option 2: Sufficient for filtration (NFP = 35 mm, positive).
- Option 3: Not sufficient for filtration (NFP < 0).
- Option 4: Not realistic as NFP cannot equal HPg.

6. **Conclusion**:
- The correct answer is **Option 2**: When the hydrostatic pressure of the blood in the glomerulus is 70 mm and the net filtration pressure is 35 mm.