USI Summer Session Chapter 18 A&P - The Heart part 5

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Cardiac cycle

all events associated with blood flow through the heart during one complete heartbeat

Systole

contraction of the heart

Diastole

relaxation of the heart

Ventricular filling

takes place in mid-to-late diastole

•AV valves are open
•80% of blood passively flows into ventricles
•Atrial systole occurs, delivering the remaining 20%

End diastolic volume

Volume of blood in each ventricle at the end of ventricular diastole

Ventricular systole

Atria relax and ventricles begin to contract

•Rising ventricular pressure results in closing of AV valves
•Isovolumetric contraction phase (all valves are closed)
•In ejection phase, ventricular pressure exceeds pressure in the large arteries, forcing the SL valves open

End systolic volume (ESV)

volume of blood remaining in each ventricle

Isovolumetric relaxation

occurs in early diastole

•Ventricles relax
•Backflow of blood in aorta and pulmonary trunk closes SL valves and causes dicrotic notch (brief rise in aortic pressure)

Cardiac Output (CO)

Volume of blood pumped by each ventricle in one minute

heart rate (HR) x stroke volume (SV)

Heart Rate

Number of beats per minute

stroke volume

volume of blood pumped out by a ventricle with each beat

SV = EDV - ESV

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