CVS - responses of the whole system Flashcards
What is the cardiac ouput like during heavy exercise?
~ 25L/min
Which organs get a decrease in the percentage of the cardiac output during heavy exercise?
GIT, kidneys, bone and brain.
Which organs receive the same percentage of the cardiac output during heavy exercise?
Heart
Which organs get a increase in the percentage of the cardiac output during heavy exercise?
Skin and skeletal muscle.
What is a typical cardiac output range?
5-15l/min (>20l/min if very unfit)
What is a typical heart rate range?
60-180bpm (upper limit 220-age)
What is the typical stroke volume range?
~60-150ml (>200 if very fit)
How is the heart rate regulated?
- Self-generated: SAN/AV node
2. Modulated - by ANS/ hormonal control
How is stroke volume regulated?
- Venous return: CVP-RAP drives ventricular filling
- Aortic pressure (drives baroreceptor sensor output)
- ANS/ hormonal control
- Cardiac fitness: ventricular distensibility/ conctractility
Where are baroreceptors found? What is the difference in the pressures they detect?
- Aortic arch - sensitive to higher pressures (>100 mmHg increase firing)
- Carotid body - sensitive to lower pressures (>50 mmHg increase firing).
What is the role of baroreceptors?
They send signals to the cardiovascular centre in the medulla when they are stretched by pressure. This results in sympathetic activity changes which modulates cardiac output (SV and HR).
What modulates the vasomotor tone of arterioles and pre-capillary sphincters and therefore TPR?
SNS, metabolites and autocoid control.
What is the role of veins/ great veins in controlling stroke volume?
They act as reservoir for blood. Their large volume and low pressure regulate RA filling and therefore stroke volume.
What is the normal range in central venous pressure?
+2-10 mmHg
Why is it serious if mean arterial blood pressure falls below 60mmHg?
Tissue perfusion becomes inadequate and if it continues for any length of time, there is a serious risk of organ failure.
