Regulation of Stroke Volume and Heart Rate Flashcards
What is the control mechanism of heart rate?
Neural
What is the regulation mechanism for stroke volume?
Preload
Afterload
Neural
Pathological
How does the sympathetic nervous system regulate heart rate?
Releases noradrenaline from nerves and adrenal medulla.
Act on Beta 1 receptors on sinoatrial node
Increases slope of pace maker potential between heart beats
Increases heart rate
What is the effect of the parasympathetic nervous system on heart rate?
Vagus nerve releases acetycholine
Acts on muscarinic receptors on sinoatrial node
Hyperpolarises cells and decreases the slope of pacemaker potential
Decreases heart rate = bradycardia
What does starlings law state?
Starling’s Law states -
Energy of contraction is proportional to initial length of cardiac muscle fibre
Why is the slope decreasing to the left side of the peak tension?
Actin filaments start to interfere with each other
What is the length of the cardiac muscle fibres proportional to?
End diastolic volume
What is the stroke volume related to?
Tension
What is preload affected by?
End diastolic volume
What ensures self regulation of stroke volume of left and right ventricles?
Proportional relationship between volume of venous return & stroke volume
What is the afterload?
The load against which muscle tries to contract
What is the aortic pressure affected by?
How much blood is pushed into aorta (cardia output)
How easy it is for blood to get out of aorta (total peripheral resistance)
Why does an increase in TPR result in a reduction in stroke volume?
TPR- Total Peripheral Resistance
Aortic pressure will increase,
Ventricle will have to work harder to push open the aortic valve
It will have less energy left to do useful bit of ejecting blood.
What is responsible for the variable portion of the total peripheral resistance?
The arterioles
What is the total peripheral resistance set by?
The arterial pressure - what sets the afterload