CVS 5.2 - Pressures and Flow in the Systemic Circulation Flashcards
What is vasomotor tone?
The continuous contraction of the muscle (so there is always some vasocontstriction)
What agonises vasomotor tone?
Sympathetic stimulation of adrenergic alpha-1 receptors
What antagonises vasomotor tone?
Vasodilator factors
What is central venous pressure?
The pressure in the great veins supplying the heart
What is systolic pressure?
The maximum pressure reached in systole
What is diastolic pressure?
The minimum pressure reached in diastole
What is pulse pressure?
The difference between systolic and diastolic pressures
What is venous return?
The rate of blood back to the heart
What is vasoconstriction?
The decrease in flow due to contraction of arterial walls
What is vasodilation?
The increase in flow due to relaxation of smooth muscle in vessel walls
What is the significance of vasoconstriction/dilation?
Means that arterioles can vary flow = control
What is total peripheral resistance? What is it proportional to?
- The total resistance to blood flow from all of the systemic vasculature (not pulmonary)
- 1/need for blood
What affects systolic pressure?
- Force of contraction
- Total peripheral resistance (more difficult to pump blood so more pressure required)
- Compliance of arteries
What affects diastolic pressure?
- Systolic pressure
- Total peripheral resistance
What is the typical value of pulse pressure?
40 mmHg
What is average pressure?
Diastolic plus 1/3rd of pulse pressure
What causes the pulse wave? Where can it be felt?
- Contraction of the ventricles which propagates along the arteries faster than blood
- Where arteries are close to the skin e.g. anatomical snuffbox
What is the significance of arteries having distensible walls?
- Stretch during systole which allows more blood to flow in than out, doesn’t increase pressure much
- Recoil during diastole which continues the flow
What is autoregulation?
When arterial pressure is within a specific range, most organs can take in the amount of blood flow they need
What is reactive hyperaemia?
- Restoration of blood flow after being stopped for a while. Leads to a large amount of blood entering after none at all
What are the effects of reactive hyperaemia?
- Continued respiration in tissues
- Vasodilators are still produced but aren’t removed
- Maximum dilation of local arterioles = very high blood flow
Why can veins sometimes be used as arterial by-pass grafts?
- At higher pressures and volumes, their compliance becomes similar to that of arteries
