Peripheral Circulation

Question 1

What is the the average width of a capillary?

Answer 1

5-10 micrometers.

Question 2

What is the average flow of blood in capillaries?

Why is this advantageous?

Answer 2

• 1mm/s.

- This increases time for exchange.

Question 3

What is Fick’s law of diffusion?

Answer 3

Rate of diffusion = permeability coefficient * concentration gradient * area

Question 4

List 3 factors which contribute to the permeability coefficient of a diffusion barrier.

Answer 4

1 - Size.

2 - Temperature.

3 - Charge.

Question 5

Give the equation for flow.

Answer 5

Flow = change in pressure / resistance.

Question 6

List 3 mechanisms of solute exchange.

Answer 6

1 - Diffusion.

2 - Vesicular transport.

3 - Bulk flow.

Question 7

What type of molecules favour diffusion for exchange?

Answer 7

Lipid soluble substances.

Question 8

What type of molecules favour vesicular transport for exchange?

Answer 8

Large charged molecules (e.g. proteins and antibodies).

Question 9

What type of molecules favour bulk flow for exchange?

Answer 9

Small molecules of molecular weight <70,000 (e.g. water and electrolytes).

Question 10

What type of capillary is required for bulk flow?

Answer 10

Fenestrated or sinusoidal capillaries.

Question 11

How does the function of the systemic circulation change along its course?

Answer 11

• Firstly distribution and resistance vessels.
• Then exchange vessels.
• Then capacitance vessels.

Question 12

List 3 differences between veins and arteries.

Answer 12

1 - Veins have less smooth muscle in the tunica media.

2 - Veins are less rigid than arteries.

3 - Veins have valves to prevent backflow.

Question 13

Describe the process by which varicose veins form.

Answer 13

1 - Gravity decreases venous return in the lower limbs.

2 - Blood-engorged veins become dilated.

3 - Incompetent valves allow backflow of blood in dilated veins.

4 - Pooling increases in the dilated veins.

Question 14

What proportion of blood is held in capacitance vessels (veins)?

Answer 14

60-80%.

Question 15

What is the advantage of a large capacitance volume?

Answer 15

Large volumes of blood can be mobilised on demand.

Question 16

What is the equation for compliance?

Answer 16

Compliance = change in volume / change in pressure.

Question 17

How does the compliance of a vein change with volume and pressure?

Answer 17

• Compliance is highest at low pressures and volumes as the vein is collapsed.
• As the vein begins to assume a more distended, circular shape, compliance decreases at higher pressures and volumes.

Question 18

How does venous tone affect venous compliance?

Answer 18

Increasing tone decreases compliance.

Question 19

List 3 ways by which venous tone can be increased.

Answer 19

1 - Sympathetic activity.

2 - Circulating catecholamines.

3 - Circulating angiotensin ii.

Question 20

What is Virchow’s triad?

What are its components?

Answer 20

• A triad of factors that contribute to thrombosis:

1 - Endothelial damage.

2 - Hypercoagulability.

3 - Stasis.

Question 21

List 3 signs of thrombosis.

Answer 21

1 - Pain.

2 - Erythema.

3 - Swelling.

Question 22

List 5 factors which contribute to central venous pressure.

Answer 22

1 - Venous capacitance.

2 - Total blood volume.

3 - Skeletal muscle pump.

4 - Respiratory pump.

5 - Gravity.