Capillary Circulation

Question 1

Define Vasomotion and the regulation of it

Answer 1

VASOMOTION = intermittent blood flow through capillaries due to contractions of metarterioles and precapillary sphincters

• Can close capillaries completely (no smooth muscle)
• Contractions related to tissue oxygenation (increased tissue usage (lower tissue oxygen contraction –> blood flows more often and larger)
• Average function: sum of ALL capillaries in a bed(increases surface area, decreases velocity)

Question 2

Describe Capillary Hydrostatic Pressure

Answer 2

Force that occurs due to blood pressure within the capillary that tends to drive fluid outward and through endothelial pores

Question 3

Describe Interstitial Colloid (Oncotic) Osmotic pressure

Answer 3

Osmotic effect due to capillary protein.
- Influence of protein which are present in the interstitium - their osmotic tendency to PULL fluid OUT to the interstitium from within the capillaries

Question 4

Describe Tissue/Interstitial Hydrostatic Pressure

Answer 4

This force drives fluid back into the capillary due to the force of the fluid in the interstitium. (normally less fluid in interstitium so Pif will be negative and fluid will move OUT of capillary)

Question 5

Describe the Capillary Colloid (Oncotic) osmotic pressure

Answer 5

Capillary oncotic pressure is the osmotic driving force due to the presence of proteins inside the capillary and tends to DRAW FLUIDS from OUTSIDE the capillary to the INSIDE of the capillary

Question 6

Define Starling Hypothesis

Answer 6

Net fluid movement:
Net Pressure = (Hydrostatic Press Cap) - (Hydrostatic Pressure Interstitium) - (Oncotic cap) + (oncotic Interstitium)
If net > 0 then fluid will move OUT of capillary (filtration)
If net < 0 then fluid will move INTO capillary (re absorption)

Question 7

What occurs to the net oncotic pressure if there is a decrease in plasma proteins?

Answer 7

the net oncotic pressure will decrease resulting in a shift downward and resulting in a greater area for more filtration

Question 8

What occurs if you decrease pressure of the Capillary?

Answer 8

The net hydrostatic pressure will also decrease, therefore, MORE REABSORPTION will occur

• increases precapillary resistance
• ex. Hemorrhage: this helps replace lost fluids being lost out of the bleeding wound.

Question 9

Describe the cause (starling forces) of edema formation

Answer 9

Interstitial edema = EXCESSIVE FILTRATION

• Increase Pressure of capillary (via from standing, heart failure, venous thrombus)
• Decreased Capillary Oncotic Pressure (via nephrotic syndrome, starvation, pregnancy)
• Changes in capillary wall (from inflamation)
• Removal of lymph “mop” (via lymph obstruction or removal)