Regulation of Stroke Volume and Heart Rate Flashcards
What is heart rate regulated by?
By the autonomic nervous system
How does the sympathetic nervous system regulate heart rate?
Sympathetic nerves release noradrenaline which, combined with circulating adrenaline from the adrenal medulla, acts on beta-1 receptors on the sinoatrial node. This increases the slope of the pacemaker potential so increases heart rate
How does the parasympathetic nervous system regulate heart rate?
Vagus nerve releases acetyl choline which acts on muscarinic receptors on the sinoatrial node. This hyper polarises cells and decreases the slope of the pacemaker potential which decreases heart rate
What does Starling’s Law state?
The energy of contraction is proportional to the initial length of the cardiac muscle fibre
What is preload?
The initial stretching of the cardiomyocytes prior to contraction
How does end diastolic volume affect preload?
Since preload is a measure of how much the heart stretches in response to end diastolic volume, the greater the EDV the greater the preload
How does preload affect stroke volume?
Increased preload, increased stroke volume
Decreased preload, decreased stroke volume
What is afterload?
The load against which the cardiac muscle tries to contract
What factors affects afterload?
How much blood is pushed into the aorta and how easy it is for that blood to leave the aorta. So total peripheral resistance and cardiac output e
affect afterload
How does afterload affect stroke volume?
As after load increase, stroke volume decreases
How does the sympathetic nervous system affect stroke volume?
Sympathetic nerves release noradrenaline which, combined with circulating adrenaline from the adrenal medulla, acts on beta-1 receptors on the myocytes. This increases contractility so gives a stronger but shorter contraction
How does the parasympathetic nervous system affect stroke volume?
It has very little effect most likely because the vagus does not innervate the ventricular muscle
What pathological mechanisms regulate stroke volume?
Hypercalcemia
Hypocalcemia
Ischaemia
What effect does hypercalcemia have on stroke volume?
Shifts curve up and left (makes it steeper)
Increases contraction strength because more calcium is flowing in and being released from inside the cell
What effect does hypocalcemia have on stroke volume?
Shifts curve down and right (less steep)
