0723 - Vessels of Systemic circulation Flashcards
Is the arterial or venous system more resistive?
Arterial (max resistance in pre-capillary sphincters). Venous system is very compliant.
How is aortic elasticity crucial in ‘filtering’ pulse wave into periphery and maintaining pressure during diastole?
The aorta has a much slower pulse wave velocity due to its comparative compliance compared to other vessels. The stiffer and smaller the artery, the faster the pulse wave.
Aorta (and other arteries) stretch during systole and rebound during diastole (windkessel effect) to maintain continuous pressure - the Mean Arterial Pressure.
What is Mean Arterial Pressure? How do you calculate it?
Key Exam Concept
The constant pressure actually responsible for perfusion.
In aorta it is mean of (120+80), in periphery it is mean of (120+2x80).
Why does the pulse wave increase in amplitude, broaden and get a second ‘hump’ in periphery
The pulse wave increases in amplitude and develops a second hump in the periphery due to reflection (essentially an echo) at the resistive elements (arterioles).
Flow velocity wave broadens due to the elastic nature of the arteries - absorbs the increase and then releases it.
How is venous volume affected by transmural pressure?
Venous system holds around 85% of TBV - very compliant at low pressure (normally), as the vein fills (increased transmural pressure), compliance drops. External pressure (i.e. muscles and gravity) determines the filling. In the thorax, on inspiration, as pleural pressure becomes negative, there is large flow in vena cava - smallest during the end of inspiration.
Why and how does muscle pump relieve venous pressure in legs?
Muscle fascia is most important aspect - keeps muscle contained and at a fairly constant volume, so pushes muscle out, compressing weins - venous valves are secondary and prevent backflow.
