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What is the cardiac cycle?
The sequence of events in one heartbeat, including systole (contraction) and diastole (relaxation) of the atria and ventricles.
What triggers the cardiac cycle?
One action potential generated by the SA node.
What are the two main phases of the cardiac cycle?
Diastole (ventricular relaxation and filling) and systole (ventricular contraction and blood ejection).
What happens during atrial diastole?
Blood flows passively into the atria from the vena cava (right atrium) and pulmonary veins (left atrium), and 70% flows passively into the ventricles.
What is atrial systole?
The contraction of the atria, pushing the remaining 30% of blood into the ventricles.
What is end-diastolic volume (EDV)?
The maximum volume of blood in the ventricles at the end of diastole, typically 120–130 mL.
What happens during isovolumetric contraction?
The ventricles contract with all valves closed, causing an increase in pressure without a change in volume.
What is stroke volume (SV)?
The amount of blood ejected by each ventricle during systole, typically 70–90 mL.
What is end-systolic volume (ESV)?
The volume of blood remaining in the ventricles after systole, typically 50 mL.
What produces the first heart sound ("LUP")?
The closure of the tricuspid and mitral valves at the start of ventricular systole.
What produces the second heart sound ("DUP")?
The closure of the aortic and pulmonary valves at the start of ventricular diastole.
What happens to atrial pressure during late diastole?
A slight increase due to atrial contraction.
What is the systolic pressure in the left ventricle and aorta?
120 mmHg.
What is the systolic pressure in the right ventricle and pulmonary artery?
25 mmHg.
Define cardiac output (CO).
The amount of blood ejected by each ventricle per minute, typically 5 L/min at rest.
How is cardiac output calculated?
CO = Stroke Volume (SV) × Heart Rate (HR).
How does exercise affect cardiac output?
It can increase 4–5 times to accommodate higher oxygen demand.
What factors influence stroke volume?
End-diastolic volume (EDV) and ventricular contractility.
What is the Frank-Starling law of the heart?
The heart pumps more forcefully as it fills more, meaning stroke volume increases with higher venous return.
What mechanisms increase venous return?
Skeletal muscle pump, respiratory pump, and venoconstriction
How does sympathetic stimulation affect contractility?
It increases contractility by enhancing calcium influx into myocardial cells, increasing stroke volume.
What is the inotropic effect?
The effect of increased ventricular contractility, often due to sympathetic activation.
How does contractility affect end-systolic volume (ESV)?
Higher contractility reduces ESV, increasing stroke volume.
How does the parasympathetic nervous system affect heart rate?
It decreases heart rate by releasing acetylcholine, increasing potassium efflux and hyperpolarization.
How does the sympathetic nervous system affect heart rate?
It increases heart rate by releasing noradrenaline, increasing calcium influx and depolarization.
How does sympathetic activity affect the AV node?
It reduces AV nodal delay, speeding up conduction to the ventricles.
What is preload?
The initial stretching of the heart muscle due to ventricular filling (EDV).
What is afterload?
The resistance the ventricles must overcome to eject blood, influenced by arterial pressure.
What is ejection fraction?
The percentage of EDV ejected during systole, typically around 60%.
What are the key determinants of cardiac output?
Heart rate (HR) and stroke volume (SV), both regulated by neural, hormonal, and intrinsic cardiac mechanisms.
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