Regulation of Stroke Volume and Heart Rate Flashcards
How is heart rate regulated?
Neural control
How is stroke volume regulated?
Reload, after load, neural and pathological
What is the collective effect of regulation of heart rate and stroke volume?
Regulation of cardiac output
How does the sympathetic nervous system regulate heart rate?
Noradrenaline and circulating adrenaline from the adrenal medulla both act on B1 receptors on SA node - increase slop of pacemaker potential and increase HR
How does the parasympathetic nervous system regulate heart rate?
Vagus nerve releases ACh, acts on muscarinic receptors on SA node - hyperpolarises cells and decreases slope of pacemaker potential which decreases heart rate
What does Starlings Law state?
The energy of contraction is proportional to the initial length of the cardiac muscle fibre
In vivo, what variable effects preload?
End Diastolic Volume
What effect does an increased venous return have on stroke volume?
Increases EDV and therefore increases stroke volume
What effect does an decreased venous return have on stroke volume?
Decreases EDV and therefore decreased stroke volume
What is the after load?
The load of blood against which the muscle tries to contract
What is TPR?
Total peripheral resistance - the ease of blood getting out of the aorta
An increased afterload decrease stroke volume?
- TPR increases
- Aortic pressure increases
- More energy required to open aortic valves
- Less energy available to force blood out of aorta
- Decreased stroke volume
Describe the neural effect on stroke volume
Noradrenaline/ circulating adrenaline act on B1 receptors increasing the contractility of myocytes - results in stronger and shorter contraction
What effect does the parasympathetic system have on the regulation of stroke volume?
Little effect because the vagus nerve does not innervate the ventricles
What pathologies have an effect on regulations of stroke volume?
- Hypercalcaemia
- Hypocalcaemia
- Ischaemia
- Barbiturates
