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Net filtration pressure is calculated by ________.
a. adding the capillary hydrostatic pressure to the
interstitial fluid hydrostatic pressure
b. subtracting the fluid drained by the lymphatic
vessels from the total fluid in the interstitial fluid
c. adding the blood colloid osmotic pressure to the
capillary hydrostatic pressure
d. subtracting the blood colloid osmotic pressure
from the capillary hydrostatic pressure
The correct answer and explanation is:
The correct answer is:
d. subtracting the blood colloid osmotic pressure from the capillary hydrostatic pressure
Explanation:
Net filtration pressure (NFP) is a crucial concept in understanding fluid exchange between capillaries and the interstitial space. It determines whether fluid will leave the capillary (filtration) or re-enter it (reabsorption).
Components of Net Filtration Pressure:
- Capillary Hydrostatic Pressure (CHP):
- This is the pressure exerted by blood against the capillary walls, which tends to push fluid out of the capillaries into the interstitial space.
- It is the primary driving force for filtration.
- Typically higher at the arterial end of the capillary bed and decreases toward the venous end.
- Blood Colloid Osmotic Pressure (BCOP):
- This is created by plasma proteins (primarily albumin) in the blood, which exert an osmotic pull, attracting water back into the capillaries from the interstitial space.
- BCOP opposes filtration and promotes reabsorption.
- Interstitial Fluid Hydrostatic Pressure (IFHP):
- This is the pressure exerted by the interstitial fluid. It can either slightly oppose or assist filtration depending on its value (usually close to zero or negative).
- Interstitial Fluid Colloid Osmotic Pressure (IFCOP):
- This refers to the osmotic pull exerted by proteins in the interstitial fluid. It is usually negligible in most tissues.
Net Filtration Pressure Formula:
NFP=(CHP+IFCOP)−(BCOP+IFHP)NFP = (CHP + IFCOP) – (BCOP + IFHP)
Simplified, NFP is largely the difference between CHP and BCOP since IFCOP and IFHP are minimal under normal conditions.
Application:
- At the arterial end, CHP dominates, leading to filtration.
- At the venous end, BCOP dominates, leading to reabsorption.
The balance of these forces is essential for maintaining fluid homeostasis in the body. Disruptions can result in edema or dehydration.