Regulation of Stroke Volume and Heart Rate Flashcards
Regulation of the heart rate is _______.
neural
The sympathetic nervous system has what effect on regulation of heart?
Tachycardia
What does the sympathetic nervous system release?
Noradrenaline released from sympathetic nerves and;
adrenaline released from the adrenal medulla.
What does noradrenaline and circulating adrenaline act on?B1 receptors on sinoatrial node
Beta-1 receptors on sinoatrial node
What impact does the sympathetic nervous system have on the SA node?
Increase slope of the pacemaker potential, pacemaker cells reach threshold quicker.
Increases heart rate (tachycardia)
What does the parasympathetic system release?
Acetylcholine (ACh)
What nerve from the parasympathetic system acts on the heart?
Vagus nerve (CN X)
What does the parasympathetic system act on?
Muscurinic receptors on sinoatrial node
What effect does the parasympathetic system have on the sinoatrial node?
Hyperpolarises cells and decreases slope of pacemaker potential.
Decreases heart rate (bradycardia)
What are the 4 things that can alter the strength of contraction (stroke volume) of the heart?
Preload
Afterload
Neural
Pathological
What does Starling’s Law state?
The energy contraction is proportional to the initial length of the cardiac muscle fibre.
How does tension of cardiac muscle fibres change with length (preload)?
Tension increases until it reaches a maximum then it decreases as the length increases.
What is the relationship between tension and length (preload) due to?
Because the over lap of the actin and myosin filaments changes, therefore the number of potential cross bridges changes also.
What is the curve of tension against length (preload) essentially the same as?
End diastolic volume against stroke volume
EDV v SV
In vivo, what affects preload?
EDV
What impact does increases venous return have on EDV and stroke volume?
EDV: increases
SV: increases
What effect does decreasing venous return have on EDV and stroke volume?
EDV: decreases
SV: decreases
What does the relationship between EDV and stroke volume ensure?
Self regulation so that the stroke volume of the left and right ventricles are the same.
Resting EDV is neither at the max or min SV.
What is afterload?
The load against which a muscle tries to contract.
What is the aortic pressure impacted by?
Total peripheral resistance (TPR)
What happens to the aortic pressure if total peripheral resistance increases?
- aortic pressure increases
- LV will have to use more work (energy) in opening the aortic valve
- SV will decrease as there is less energy for the ejection phase of contraction.
What happens to stroke volume if total peripheral resistance increases?
It decreases
What affects the afterload of the heart?
The aortic pressure which in turn is determined by TPR.
What kind of vessels affect preload?
capacitance (veins/venules)
