Which statement describes capillary fluid exchange?

Which statement describes capillary fluid exchange?

• A. Capillary hydrostatic pressure promotes reabsorption
• B. Plasma oncotic pressure promotes filtration
• C. Interstitial hydrostatic pressure promotes filtration
• D. Net filtration occurs when capillary hydrostatic pressure exceeds plasma oncotic pressure

Answer: (D)

Capillary fluid exchange is driven by Starling forces: the capillary hydrostatic pressure pushes fluid out of the capillaries into the surrounding interstitial space, while the plasma oncotic pressure pulls fluid back into the capillaries. Net filtration occurs when the outward force from capillary hydrostatic pressure exceeds the inward force from plasma oncotic pressure. This balance explains why fluid tends to leave the capillaries and move into the interstitium when Pc is higher than πc. Capillary hydrostatic pressure promoting reabsorption would be incorrect because its main effect is to push fluid out, not in. Plasma oncotic pressure promoting filtration is also incorrect, since it acts to draw fluid into the capillaries. Interstitial hydrostatic pressure promoting filtration is not accurate because higher interstitial pressure actually tends to push fluid back toward the capillaries, opposing filtration.

Capillary fluid exchange is driven by Starling forces: the capillary hydrostatic pressure pushes fluid out of the capillaries into the surrounding interstitial space, while the plasma oncotic pressure pulls fluid back into the capillaries. Net filtration occurs when the outward force from capillary hydrostatic pressure exceeds the inward force from plasma oncotic pressure. This balance explains why fluid tends to leave the capillaries and move into the interstitium when Pc is higher than πc.

Capillary hydrostatic pressure promoting reabsorption would be incorrect because its main effect is to push fluid out, not in. Plasma oncotic pressure promoting filtration is also incorrect, since it acts to draw fluid into the capillaries. Interstitial hydrostatic pressure promoting filtration is not accurate because higher interstitial pressure actually tends to push fluid back toward the capillaries, opposing filtration.