Microcirculation

Question 1

What is the ratio of pre- to post-capillary resistance vessels and what does this mean?

Answer 1

4:1, meaning that there is much more resistance in pre-capillary vessels (ie, arterioles and metarterioles)

Question 2

What is one of the main functions of capillary filtration?

Answer 2

It washes the interstitial space of waste products by moving fluid and exchanging nutrients into and out of the capillary.

Question 3

Is there a greater outflow of fluids at the arterial or venous end? Why?

Answer 3

There is a greater outflow of fluids at the arterial end due to a higher blood pressure, therefore a larger hydrostatic force that drives fluids out of the arterial end of the capillary.

Question 4

What is the equation for Fick’s Law and what does it mean?

Answer 4

J = -PS(Co-Ci)
The quantity of substance moved per time is proportional to the capillary permeability, capillary surface area, and concentration gradient of the diffused substance

Question 5

What are the 4 factors governing trans-capillary fluid exchange?

Answer 5

• plasma oncotic pressure
• capillary hydrostatic pressure
• tissue oncotic pressure
• interstitial hydrostatic pressure

Question 6

What does the Starling Hypothesis of capillary filtration state?

Answer 6

the flow of fluids across capillary walls depends on the balance b/t force of BP on the walls (hydrostatic pressure) and osmotic force

Question 7

An increase in ______ pressure will exert a greater increase in capillary hydrostatic pressure than an increase in ______ pressure.

Answer 7

venous; arterial

Question 8

Why does venous pressure exert a large effect on capillary hydrostatic pressure, but arterial pressure only exerts a small effect?

Answer 8

due to low post-capillary resistance (there is nothing on the venous side to keep fluid from flowing backward and backing up… on the arterial side, there are arterioles and sphincters that contribute to high pre-capillary resistance)

Question 9

Does pulmonary HTN cause pulmonary edema?

Answer 9

No, because the pulmonary artery is before the pulmonary circuit, so backup will occur in the RV and RA.

Question 10

What condition can cause an increase in venous pressure?

Answer 10

left ventricular heart failure (LVHF), in which pressure backs up into the left atrium, pulmonary veins (leading to pulmonary edema), right side of the heart, and eventually the venous system

Question 11

What is the total osmotic pressure of plasma?

Answer 11

~6000 mmHg (very high!)

Question 12

What is the key factor that holds fluid within the capillaries?

Answer 12

osmotic pressure of plasma proteins

Question 13

Why does albumin exert a greater osmotic force than would be expected?

Answer 13

It has a negative charge, thus electrostatically interacting with positively charged ions like K+ and Na+ and retaining them in the vascular space.

Question 14

What is the purpose of the lymphatic system?

Answer 14

It collects and returns interstitial fluid to the circulatory system.

Question 15

Where do the collecting vessels of the lymphatic system go?

Answer 15

to the subclavian vein

Question 16

What are the factors affecting lymph flow?

Answer 16

• capillary filtration (filtered fluid picked up by lymphatics)
• muscular activity
• lymphatic valves (unidirectional)

Question 17

What are some of the main precipitating factors of peripheral edema?

Answer 17

• reduction in plasma protein concentration (<2.5 g/dl of serum albumin)
• increase in capillary hydrostatic pressure (venous pressure)
• increase in permeability of capillary membrane
• lymphatic obstruction (parasites, swelling, tumor)