Peripheral Circulation Flashcards
What is the the average width of a capillary?
5-10 micrometers.
What is the average flow of blood in capillaries?
Why is this advantageous?
- 1mm/s.
- This increases time for exchange.
What is Fick’s law of diffusion?
Rate of diffusion = permeability coefficient * concentration gradient * area
List 3 factors which contribute to the permeability coefficient of a diffusion barrier.
1 - Size.
2 - Temperature.
3 - Charge.
Give the equation for flow.
Flow = change in pressure / resistance.
List 3 mechanisms of solute exchange.
1 - Diffusion.
2 - Vesicular transport.
3 - Bulk flow.
What type of molecules favour diffusion for exchange?
Lipid soluble substances.
What type of molecules favour vesicular transport for exchange?
Large charged molecules (e.g. proteins and antibodies).
What type of molecules favour bulk flow for exchange?
Small molecules of molecular weight <70,000 (e.g. water and electrolytes).
What type of capillary is required for bulk flow?
Fenestrated or sinusoidal capillaries.
How does the function of the systemic circulation change along its course?
- Firstly distribution and resistance vessels.
- Then exchange vessels.
- Then capacitance vessels.
List 3 differences between veins and arteries.
1 - Veins have less smooth muscle in the tunica media.
2 - Veins are less rigid than arteries.
3 - Veins have valves to prevent backflow.
Describe the process by which varicose veins form.
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.
What proportion of blood is held in capacitance vessels (veins)?
60-80%.
What is the advantage of a large capacitance volume?
Large volumes of blood can be mobilised on demand.
What is the equation for compliance?
Compliance = change in volume / change in pressure.
How does the compliance of a vein change with volume and pressure?
- 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.
How does venous tone affect venous compliance?
Increasing tone decreases compliance.
List 3 ways by which venous tone can be increased.
1 - Sympathetic activity.
2 - Circulating catecholamines.
3 - Circulating angiotensin ii.
What is Virchow’s triad?
What are its components?
- A triad of factors that contribute to thrombosis:
1 - Endothelial damage.
2 - Hypercoagulability.
3 - Stasis.
List 3 signs of thrombosis.
1 - Pain.
2 - Erythema.
3 - Swelling.
List 5 factors which contribute to central venous pressure.
1 - Venous capacitance.
2 - Total blood volume.
3 - Skeletal muscle pump.
4 - Respiratory pump.
5 - Gravity.
