Regulation of SV and HR Flashcards
What regulates HR?
Neural
What regulates stroke volume?
- Preload
- Afterload
- Neural
- Pathological
What part of the nervous system controls HR?
Autonomic
What neurotransmitter is released by the sympathetic system to increase HR?
Noradrenaline
Where else can the noradrenaline come from that increases HR?
Adrenal medulla
What receptors does the noradrenaline act on?
B1 receptors
Where are the B1 receptors that the noradrenaline acts on?
Sinoatrial node
What effect does the sympathetic this have on the pacemaker potential?
Increases slope
What neurotransmitter is released by the parasympathetic system?
ACh
What cranial nerve slows HR?
Vagus
What receptors are acted on by the ACh released by the parasympathetic system?
Muscarinic receptors in the SA node
What effect does the ACh have on pacemaker cells?
Hyperpolarises them
What effect does ACh have on the slope of the pacemaker potential?
Decreases slope
What does starlings law state?
The energy of contraction is proportional to the initial length of the cardiac muscle fibre
What is the length of the cardiac muscle fibre known as?
Preload
What is preload affected by?
End diastolic volume
What effect would an increased/decreased venous load have on EDV?
Increased load = higher EDV
Decreased load = lower EDV
What happens to stroke volume as EDV increases/decreases?
- Stroke volume increases as EDV increases
- Stroke volume decreases as EDV decreases
How does the directly proportional relationship of EDV and SV ensure self regulation?
Means the SV of the left and right ventricles is equal
What is afterload?
The load against which the muscle fibre contracts
In what two ways is aortic pressure affected?
- How much blood is pushed into the aorta (CA)
- How easy it is for the blood to get out of the aorta (TPR)
If TPR increases what will happen to the ventricle and stroke volume?
- Ventricle will have to work harder to open the aortic valve
- Less energy will remain to actually inject the blood so STROKE VOLUME decreases
What vessels affect preload?
Capacitance
What vessels affect afterload?
Resistance
What effect does the sympathetic system have on stroke volume?
Increases it
What receptors does the sympathetic system release noradrenaline into to increase SV?
- B1 receptors on myocytes
How does the sympathetic system effect contraction time?
Gives a shorter but stronger contraction (chronotropic effect)
How does the parasympathetic system effect stroke volume
- Doesn’t really
- Vagus doesn’t innervate ventricular muscle
What effect will hypercalcaemia have on SV?
- Shifts curve up and left (stronger shorter contraction)
What effect will hypocalcaemia have on SV?
- Shifts curve down and right (longer weaker contraction)
What effect will ischaemia have on SV?
- Shifts curve down and right (longer weaker contraction)
How does starling’s law allow the heart to compensate for a reduced pumping ability?
- Allows the heart to work around a bigger EDV
- Results in a lower ejection fraction and reduced exercise capacity
What effect will barbiturates have on stroke volume?
Shifts curve down and right (longer weaker contraction)
In what ways can the cardiac output be controlled?
- HR Increase
- Contractility increase
- Venous return increase
- TPR fall
How does an increase in contractility effect the CO?
Alters ionotropic state and shortens systole
How does a venous return increase affect CO?
- Venoconstriction
- Maintains preload
How does a fall in TPR control CO?
Reduces afterload
