Capillary Exchange: Transport Routes and Fluid Balance

All flashcards

Bulk flow

Pressure-driven mass movement of fluid between capillaries and the surrounding interstitial fluid.

Filtration

Movement of fluid out of a capillary and into the interstitial fluid.

Reabsorption

Movement of fluid from the interstitial fluid back into a capillary.

Blood colloidal osmotic pressure (BCOP)

Inward-pulling osmotic pressure produced by plasma proteins that largely remain in the blood.

Lymph

Excess interstitial fluid collected by lymphatic vessels.

Quiz questions

1. Under the simplified conditions described for capillary exchange, which relationship defines net filtration pressure (NFP)?Answer: $\text{NFP} = \text{CHP} - \text{BCOP}$
2. At the arterial end of a capillary, CHP is 35 mm Hg and BCOP is 25 mm Hg. What is the NFP and its usual effect?Answer: +10 mm Hg; it favors filtration.
3. Why does blood colloidal osmotic pressure usually promote reabsorption?Answer: Plasma proteins largely remain in blood, drawing water toward the capillary.
4. What is the typical net fluid-volume change near the middle of a capillary when CHP and BCOP are approximately equal?Answer: There is no net change, although fluid moves in both directions.
5. How does excess interstitial fluid collected by lymphatic vessels eventually return to the bloodstream?Answer: Lymphatic ducts drain into the subclavian veins.