12. Responses of the Whole System Flashcards
How is CVS output regulated?
The heart rate is self generated by the SAN AVS, it is modulated by ANS and hormonal control.
The stroke volume depends on venous return and aortic pressure, baroreceptors sensor output. It is controlled by ANS and hormonal control, also depends on ventricular distensibility and contractility.
What is the rest CVS system mean arterial blood pressure?
95mmHg.
Why must the mean arterial blood pressure stay above 60mmHg?
To provide adequate pressure to perfuse and drive blood through the whole vasculature.
What happens to respond to postural change with the cardiovascular system?
Recumbent posture, 65% blood in the venous system. When you stand up, gravity re-distributes the blood so the legs both take up an extra 500ml of blood. Central venous pressure falls so by Starlings law, stroke volume falls. Mean arterial pressure also falls by 20-25mmHg.
How does the CVS respond to the fall in mean arterial pressure from standing up?
ANS control in the orthostatic response. Heart rate rises and TPR drops briefly. Muscle tone of the vasculature increases. The muscle pump in the legs drives blood upwards.
What is the effect on the CVS of eating a large meal?
Systemically ANS and PSNS activity increases. Local autacoids and vasodilator a increase blood flow to the the GI tract. TPR decreases. Baroreceptors detect the fall in mean arterial pressure. Increased CVP is reduced by extra pumping of the heart. Arterial pressure raises to normal so GI blood flow increases to meet the demand. CVS goes back to normal and MABP adjusts cardiac output.
What is the effect on the venous supply of eating a large meal?
TPR falls so there is an initial fall in arterial pressure. Flow out through the liver increases so central venous pressure rises. This increases right atrium filling so cardiac output rises.
What is the acute effect on CVS of intense exercise?
Peak flow demand is increased. There is a huge increase in substrate demand, this is matched by a decrease in TPR. Vasodilator so increase K+H+ lactate adenosine. Endothelial autacoids are released and reduce SNS effect locally.
How long does exercise induced hyperaemia take to set in?
A few seconds, it’s very rapid.
How does the CVS respond to intense exercise?
Central voluntary control, brain increases heart rate with expectation of exercise.
Baroreceptors signal acute exercise induced increase in blood pressure, so HR and SV increase.
Skeletal muscle’s contractile activity actively aids whole circulation of blood.
How can haemorrhaging lead to hypovolemic shock, where tissues can’t be perfused?
There is an acute major loss of blood, although this is stopped by clotting. If residual blood volume falls to 3.5/4 litres or less, the patient will go into hypovolemic shock and their MABP will fall below the safety line of 65mmHg.
How does the CVS respond to haemorrhaging?
Baroreceptors signal severe drop in blood pressure. So there is a very large SNS output to increase HR and SV, also to arterioles so TPR increases to keep MABP high enough, also to the veins to keep CVP up and SV. Tachycardia sets in and everywhere but the heart and brain has decreased supply. This can lead to kidney failure.
