Cardiac Cycle, Valves, and Pressure Changes
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47 Terms
What is the cardiac cycle?
One complete heartbeat, including contraction and relaxation of atria and ventricles.
What is systole?
Contraction phase.
What is diastole?
Relaxation/filling phase.
Main steps of the cardiac cycle
Ventricular filling → atrial systole → isovolumetric contraction → ventricular ejection → isovolumetric relaxation.
During ventricular filling, what are the atria doing?
Relaxing and filling with blood.
During ventricular filling, what are the ventricles doing?
Relaxing and filling with blood.
Valves during ventricular filling
AV valves open, semilunar valves closed.
Why are AV valves open during ventricular filling?
Atrial pressure is greater than ventricular pressure.
Why are semilunar valves closed during ventricular filling?
Arterial pressure is greater than ventricular pressure.
What is passive ventricular filling?
Blood flows from atria into ventricles without atrial contraction.
What is atrial systole?
Atrial contraction that pushes the final amount of blood into ventricles.
What percentage of ventricular filling is usually caused by atrial systole?
About 20%.
What volume is reached at the end of ventricular filling?
End-diastolic volume, or EDV.
What is EDV?
Amount of blood in a ventricle at the end of diastole, before contraction.
During atrial systole, what valves are open?
AV valves are open.
During atrial systole, what valves are closed?
Semilunar valves are closed.
What is ventricular systole?
Ventricular contraction.
What is isovolumetric contraction?
Early ventricular systole when ventricles contract but no blood leaves because all valves are closed.
What causes AV valves to close?
Ventricular pressure becomes greater than atrial pressure.
What heart sound is caused by AV valves closing?
S1, the “lub” sound.
During isovolumetric contraction, what happens to ventricular pressure?
It rises quickly.
During isovolumetric contraction, what happens to ventricular volume?
It stays the same.
Why does ventricular volume not change during isovolumetric contraction?
All valves are closed.
When do semilunar valves open?
When ventricular pressure exceeds pressure in the pulmonary trunk or aorta.
What is ventricular ejection?
The phase when blood is pumped out of ventricles into the arteries.
Valves during ventricular ejection
AV valves closed, semilunar valves open.
During ventricular ejection, what happens to ventricular volume?
It decreases.
What volume remains after ventricular ejection?
End-systolic volume, or ESV.
What is ESV?
Amount of blood left in a ventricle after contraction.
What is isovolumetric relaxation?
Early ventricular diastole when ventricles relax but all valves are closed.
What causes semilunar valves to close?
Arterial pressure becomes greater than ventricular pressure.
What heart sound is caused by semilunar valves closing?
S2, the “dub” sound.
During isovolumetric relaxation, what happens to ventricular pressure?
It decreases quickly.
During isovolumetric relaxation, what happens to ventricular volume?
It stays the same.
Why does volume not change during isovolumetric relaxation?
All valves are closed.
When do AV valves reopen?
When ventricular pressure falls below atrial pressure.
What happens after AV valves reopen?
Ventricular filling begins again.
Pressure graph: when does left ventricular pressure rise sharply?
During isovolumetric contraction.
Pressure graph: when does aortic pressure rise?
During ventricular ejection after the aortic valve opens.
Pressure graph: when does aortic pressure briefly notch?
When the aortic valve closes, creating the dicrotic notch.
Pressure graph: when does left ventricular pressure fall sharply?
During isovolumetric relaxation.
Pressure graph: why does left atrial pressure rise during ventricular systole?
The atrium is filling while the AV valve is closed.
Pressure graph: when does the mitral valve open?
When left ventricular pressure falls below left atrial pressure.
Pressure graph: when does the mitral valve close?
When left ventricular pressure rises above left atrial pressure.
Pressure graph: when does the aortic valve open?
When left ventricular pressure rises above aortic pressure.
Pressure graph: when does the aortic valve close?
When aortic pressure rises above left ventricular pressure.
Draw-card: Cardiac cycle pressure graph
Draw left atrial, left ventricular, and aortic pressure curves; label filling, atrial systole, isovolumetric contraction, ejection, isovolumetric relaxation, and valve openings/closings.