Multiple Choice
An important factor directly affecting the glomerular filtration rate is __________.
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25. The Urinary System
Renal Physiology Step 1: Glomerular Filtration
Problem 16
Textbook Question
Net filtration pressure in most capillary beds favors:
a. Absorption
b. Osmosis
c. Filtration
d. Secretion
Verified step by step guidance1
Understand the concept of net filtration pressure (NFP): NFP is the balance of hydrostatic pressure and osmotic pressure across the capillary walls, determining the movement of fluid either into or out of the capillaries.
Identify the forces involved: Hydrostatic pressure pushes fluid out of the capillaries, while osmotic pressure (due to plasma proteins) pulls fluid into the capillaries. These forces oppose each other.
Apply the formula for net filtration pressure: NFP = (Capillary hydrostatic pressure + Interstitial osmotic pressure) - (Capillary osmotic pressure + Interstitial hydrostatic pressure). This formula helps determine whether filtration or absorption occurs.
Determine the typical values in most capillary beds: In most capillary beds, hydrostatic pressure is higher than osmotic pressure, favoring the movement of fluid out of the capillaries, which is known as filtration.
Conclude the physiological process: Based on the balance of pressures, net filtration pressure in most capillary beds favors filtration, as fluid is pushed out of the capillaries into the interstitial space.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Net Filtration Pressure
Net filtration pressure (NFP) is the difference between the hydrostatic pressure and the osmotic pressure within capillaries. It determines the direction and rate of fluid movement across capillary walls. A positive NFP indicates that fluid is likely to leave the capillary (filtration), while a negative NFP suggests fluid is being reabsorbed.
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Filtration
Filtration is the process by which fluid and solutes move from the capillaries into the interstitial space due to pressure differences. In the context of capillary beds, filtration occurs when the hydrostatic pressure within the capillaries exceeds the osmotic pressure, leading to the movement of water and small molecules out of the bloodstream.
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Osmosis
Osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. While it plays a crucial role in maintaining fluid balance in the body, in the context of capillary beds, it is primarily the osmotic pressure that counteracts filtration, influencing the reabsorption of fluid back into the capillaries.
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