Microcirculation

Question 1

What are the major constituent vessels in the microcirculation?

Answer 1

Arterioles, capillaries, venules, precapillary sphincters, arteriovenous anastomoses, lymphatics

Question 2

Why don’t capillaries burst?

Answer 2

Wall tension = pressure x radius

• The radius is incredibly small in capillaries
• The pressure drops significantly in the arterioles

Question 3

How can the velocity of capillary flow be determined?

Answer 3

Velocity = Blood flow/Cross sectional area

Question 4

What are the three main functions of the capillaries?

Answer 4

1) Exchange of gases and nutrients
2) Filtration and reabsorption of fluids
3) Secretion of NO and ACE by endothelium

Question 5

What are factors involved in the amount of diffusion that occurs?

Answer 5

1) The diffusion coefficient of a molecule
2) the surface area of the diffusion pathway
3) The concentration gradient across the capillary membrane
4) The thickness of the barrier

Question 6

How is the net flow of fluid determined?

Answer 6

a filtration coefficient x difference between filtration and reabsorption
Filtration coefficients differ in each type of capillary bed

The net result is usually filtration

Question 7

How is filtration calculated?

Answer 7

Capillary hydrostatic pressure (Pc) [this changes along the length of the capillary] + interstitial oncotic pressure (πi)

Question 8

How is reabsorption calculated?

Answer 8

Interstitial hydrostatic pressure (Pi)+ capillary oncotic pressure (πc)

Question 9

How is capillary hydrostatic pressure determined by:

1) Arterial pressure
2) arteriolar resistance
3) venous resistance
4) Venous Pressure

Answer 9

Increases with 1, 3, 4

Decreases with 2