Regulation of Stroke Volume and Heart Rate Flashcards
How does the sympathetic nervous system speed up heart rate?
Nerves release noradrenaline which act on beta 1 receptors on SA node increasing slope of pacemaker potential and increasing heart rate
How does the parasympathetic system decrease heart rate?
Vagus nerve releases Ach which acts on muscarinic receptors on SA node.
Hyper polarises cells and decreases slope of pacemaker potential
Heart is constantly under this restraint
What is preload affected by?
End diastolic volume
Increased venous return leads to increased EDV and thus increased stroke volume
Ensures self regulation
What is afterload?
Load against which muscle tries to contract
What is aortic pressure affected by?
How much blood is pushed into the aorta
How easy it is for that blood to get out the aorta
What happens if TPR increases?
Aortic pressure increases thus ventricle must work harder to push open aortic valve and so stroke volume decreases
What effect does the sympathetic system have on stroke volume?
Noradrenaline acts on beta 1 receptors on myocytes increasing contractility
What effect does the parasympathetic system have on stroke volume?
Little effect as does not innervate
What effect does hypercalcaemia have on stroke volume?
Increase in calcium concentration in blood leads to more calcium producing more x bridges which shifts curve up and left and produces stronger contraction
What effect does hypocalcaemia have on stroke volume?
Shifts curve down and right
What effect does ischaemia have on stroke volume?
Transient loss of blood supply to cardiac muscle shifts curve down and right
What effect do barbiturates have on stroke volume?
Shifts curve down and right
What is cardiac output equal to?
Heart rate x stroke volume
Why does SV decrease at high heart rates?
Shortened cardiac interval cuts into rapid filling phase reducing EDV and this preload and stroke volume
