Colloid Osmotic Pressure and Capillary Bulk Flow

Thirty question-and-answer flashcards reviewing colloid osmotic pressure, bulk flow, plasma proteins, and their role in maintaining blood pressure.

1) What is colloid osmotic pressure?

The osmotic force created by plasma proteins that pulls water back into capillaries, helping maintain blood volume and pressure.

2) Where in the circulation does colloid osmotic pressure act most directly?

At the capillary beds, especially on the venule end.

3) Why is colloid osmotic pressure crucial for blood pressure maintenance?

Because returning fluid to the bloodstream preserves blood volume; reduced volume would lower blood pressure.

4) Which end of a capillary bed has higher hydrostatic (blood) pressure, arterial or venule?

The arterial end.

5) Name two substances that typically leave the capillary during exchange with tissues.

Oxygen and glucose (others include ions and hormones).

6) What is bulk flow transport?

The mass movement of fluid and dissolved solutes out of or into capillaries driven by pressure gradients.

7) What primary force drives fluid out of the arterial end of capillaries during bulk flow?

Hydrostatic (blood) pressure.

8) Can plasma proteins readily exit capillaries through bulk flow?

No, they are too large to pass through the capillary filtration pores.

9) Why are plasma proteins retained inside the capillary lumen?

Their large molecular size prevents them from fitting through the small filtration openings.

10) What happens to the concentration of plasma proteins in the venule end after fluid has filtered out?

It increases, creating a higher solute concentration than in the arterial end or interstitial fluid.

11) How does this higher protein concentration affect water movement?

It draws water back into the capillary by osmosis.

12) What process moves water toward an area of higher solute concentration?

Osmosis.

13) In osmosis, water moves from ____ solute concentration to ____ solute concentration.

Lower; higher.

14) In this lecture, what does the term “filtered” mean?

Movement of fluid and small solutes from the capillary lumen into the interstitial fluid.

15) What garden-device analogy was used to describe fluid seepage from capillaries?

Soaker hoses with tiny perforations that let water slowly seep out.

16) What would happen to systemic blood pressure if filtered fluid were not reabsorbed?

Blood pressure would fall due to loss of blood volume.

17) List three transport pathways across capillary walls other than bulk flow.

Paracellular pathways, transcellular (across endothelial cells), and fenestrations.

18) What are fenestrations in a capillary?

Small pores within endothelial cells that facilitate exchange of fluids and small solutes.

19) Define paracellular transport.

Movement of substances between adjacent endothelial cells.

20) Failure of colloid osmotic pressure could lead to what clinical condition?

Edema (excess interstitial fluid).

21) Why is colloid osmotic pressure significant even though each capillary loses only a small amount of fluid?

Because the body contains millions of capillary beds, so cumulative fluid loss would be enormous without reabsorption.

22) In the lecture illustration, what color represented plasma proteins?

Orange.

23) Which segment of the capillary bed is primarily responsible for fluid reabsorption?

The venule (venous) end.

24) Describe the relationship between blood volume and blood pressure.

Blood pressure is directly proportional to blood volume; less volume means lower pressure.

25) What term describes movement of substances from blood to interstitial fluid?

Filtration (or bulk flow when referring to fluid).

26) Which physiology textbook was cited for the soaker-hose analogy?

Silverthorne.

27) Why is it inaccurate to say more plasma proteins are produced at the venule end?

The number of proteins is unchanged; only their concentration rises because water has left the vessel.

28) What main solute is responsible for creating colloid osmotic pressure in capillaries?

Plasma proteins (especially albumin).

29) How do plasma proteins establish an osmotic gradient?

By remaining in the bloodstream and increasing solute concentration relative to the interstitial fluid, attracting water inward.

30) What tiny vascular structures collectively determine large-scale fluid balance in the body?

Capillary beds spread throughout all tissues.