Topic 1 CVS Lecture 5 Flashcards
Why is blood flow out of the heart intermittent but blood flow in the arteries continuous?
Blood flow out of the heart is intermittent because it only flows out during ventricular systole. The arteries have continuous flow because they act as pressure reservoirs by expanding during the high pressure of systole and then returning to their normal state during diastole. This allows continuous flow.
What is the dichrotic notch and what causes it.
It is a small downward jump in the arterial pressure that coincides with the closing of the semilunar valves. It can be used as a signal that systole has ended. It happens because the pressure drops due to there no longer being blood flow from the heart. It picks up again as the arteries contract.
What is pulse pressure?
The pressure difference between systole and diastole.
PP = SBP - DBP
What is mean arterial pressure (MAP) and how is it calculated?
It is an estimate of the blood pressure in the arteries and is calculated by MAP = DBP + (1/3)(PP).
What is hypertension?
A blood pressure that is consistently above 140/90
What is Hypotension?
A blood pressure consistently below 100/60
How is blood flow to different organs/tissues regulated?
It is regulated by changing the diameter and therefore resistance of local arterioles. This alters flow as flow is F = Pdifference/R
How does metabolic control perform the autoregulation of arteriole blood flow.
Local chemical factors will either relax or constrict the smooth muscle around the arterioles. For eg a local increase in [CO2] will cause the arteriole smooth muscle to relax and therefore increase blood flow.
What is active hyperaemia?
It is the increased blood flow to a tissue induced by local chemical products of increased metabolism.
What is the myogenic mechanism?
It is the reaction of arterial smooth muscle to stretch and relaxation. It is the body’s way of maintaining constant flow to organs in times of changed MAP.
What 2 systems can be used to coordinate the control of arterioles throughout the body.
Neuronal control and hormonal control
How does neuronal control of arterioles alter blood supply to a tissue or organ?
Most arterioles are richly innervated by the sympathetic nervous system. Sympathetic nerves release the neurotransmitter noradrenaline which acts on smooth muscle adrenoreceptors (alpha-1) which cause smooth muscle contraction and therefore constriction of the arterioles.
What is the resting level of sympathetic innervation of arterial smooth muscle? Why do we have this?
There is some resting level of sympathetic innervation so that arterioles are somewhat constricted. This allows them to be dilated by reducing sympathetic innervation as well as constricted by increasing sympathetic innervation.
What is the effect of hormonal adrenaline on arterioles?
It causes constriction in most areas (alpha-receptors) but causes dilation when acting on arterioles with beta2 adrenoreceptos (skeletal muscle)
Name some neruonal, hormonal and local vasoconstrictors.
Neuronal - sympathetic release of noradrenaline to alpha receptors
Hormonal - Adrenaline (alpha receptors), Angiotensin II, ADH
Local - Internal blood pressure (myogenic mechanism), endothelial endothelin-1
