Which of the following defines the net filtration pressure (NFP)?

Options

A. BCOP-(GHP+CHP)
B. GHP-(BCOP+CHP)
C. (BCOP+GHP)-CHP
D. (GHP-CHP)+BCOP

Answer

To determine the definition of net filtration pressure (NFP), we can break down the components involved in the filtration process in the kidneys. Here’s a step-by-step solution:

### Step 1: Understand the Components
1. **Blood Colloidal Osmotic Pressure (BCOP)**: This is the pressure exerted by proteins in the blood plasma that tends to pull water back into the capillaries. It opposes filtration.

2. **Glomerular Hydrostatic Pressure (GHP)**: This is the pressure exerted by the blood within the glomeruli. It promotes filtration by pushing water and solutes out of the blood and into the Bowman’s capsule.

3. **Capsular Hydrostatic Pressure (CHP)**: This is the pressure exerted by the fluid in the Bowman’s capsule that opposes filtration by pushing back against the fluid being filtered.

### Step 2: Define Net Filtration Pressure (NFP)
Net Filtration Pressure (NFP) can be defined as the total pressure that promotes filtration in the kidneys. It is calculated using the following formula:

\[ \text{NFP} = \text{GHP} - (\text{BCOP} + \text{CHP}) \]

This means that NFP is the glomerular hydrostatic pressure minus the sum of the opposing pressures (BCOP and CHP).

### Step 3: Analyze the Options
Now, we can analyze the provided options to find the correct definition of NFP:

1. **Option A**: BCOP - GHP (Incorrect, as BCOP is opposing)
2. **Option B**: GHP - (BCOP + CHP) (Correct, as it correctly accounts for the promoting and opposing pressures)
3. **Option C**: GHP + BCOP (Incorrect, as it does not account for opposing forces)
4. **Option D**: GHP + CHP (Incorrect, as it does not represent the opposing forces correctly)

### Final Answer
The correct definition of net filtration pressure (NFP) is given by:

\[ \text{NFP} = \text{GHP} - (\text{BCOP} + \text{CHP}) \]

Thus, the correct option is **Option B**.

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