Microcirculation

Question 1

What is microcirculation?

Answer 1

The flow of blood from an arteriole to a venule, through a capillary bed or vascular shunt

Question 2

What are the 4 vessels involved in microcirculation?

Answer 2

1. Pre-capillary arteriole
2. Precapillary sphincters and vascular shunt
3. Caillary bed
4. Post-capillary venule

Question 3

Describe a pre-capillary arteriole

Answer 3

• smallest type of artery
• connects with capillary bed via pre-capillary sphincters or feeds into vascular shunt to bypass capillary bed
• vasodilates in inflammatory response to increase blood flow to injured tissue

Question 4

Describe a capillary bed

Answer 4

interconnected network of capillaries
- where exchange of nutrients, oxygen and waste occurs between bloodstream and interstitial fluid through tunica intima of capillaries

Question 5

Describe a post-capillary venule

Answer 5

• venule receiving blood from capillaries in capillary bed, or blood that has been diverted via the vascular shunt around the capillary bed
• increased vascular permeability at post-capillary venule in inflammatory response increases delivery of oxygen, nutrients and neutrophils to tissue

Question 6

Which blood vessels in microcirculation are responsible for vasodilation and increased vascular permeability in inflammatory response?

Answer 6

Pre-capillary arteriole: vasodilation (delivers more blood to tissue)

Post-capillary venule: increased vascular permeability (increases delivery of oxygen, nutrients and neutrophils to tissue)

Question 7

What is the difference between hydrostatic pressure and osmotic pressure?

Answer 7

Hydrostatic pressure: caused by fluid pressing against a boundary that ‘push’ fluid across boundary

Osmotic pressure: pressure caused by albumin proteins in blood that ‘pull’ fluid toward them

Question 8

What is the balance of hydrostatic and osmotic pressure at the arterial end of microcirculation?

Answer 8

Hydrostatic pressure (blood pressure) is higher than osmotic pressure - this pushes blood out of the capillary into the interstitial fluid

Question 9

What is the balance of hydrostatic and osmotic pressure at the venous end of microcirculation?

Answer 9

Hydrostatic pressure in the vessel is lower than capillary colloid osmotic pressure - this ‘pulls’ fluid back into the capillary from the interstitial fluid

Question 10

Which protein in the blood is responsible for osmotic pressure?

Answer 10

Albumin

Question 11

What is the role of hydrostatic and osmotic pressures in the interstitial fluid?

Answer 11

Both are minimal in healthy individuals

If hydrostatic pressure in interstitial fluid is too high: causes venous incompetence & venous obstruction (not enough fluid is being pushed from capillaries into interstitial fluid)

If osmotic pressure in interstitial fluid is too high:
‘pulls’ too many proteins into the interstitial fluid, causes inflammation