University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2019
Views:

199

Pages:

5
Author:

avpillep1

Phases of Cardiac Cycle 1) 2) 3) 4) 5) Quiescent period Ventricular filling Isovolumetric contraction Ventricular ejection Isovolumetric relaxation 1) Quiescent period – all chambers relaxed – AV valves open – blood flowing into ventricles 2) Ventricular Filling – SA node fires, atria depolarize – P wave appears on ECG – atria contract, force additional blood into ventricles – ventricles now contain end-diastolic volume (EDV) of about 130 ml of blood 3) Isovolumetric Contraction of Ventricles • Atria repolarize and relax • Ventricles depolarize • QRS complex appears in ECG • Ventricles contract • Rising pressure closes AV valves - heart sound S1 occurs • No ejection of blood (no change in volume) 4) Ventricular Ejection • Rising pressure opens semilunar valves • Rapid ejection of blood • Stroke volume: amount ejected – about 70 ml at rest • End-systolic volume: amount left in heart • SV/EDV= ejection fraction, at rest ~ 54%, during vigorous exercise as high as 90%, diseased heart < 50% • Both ventricles must eject same amount of blood 5) Isovolumetric Relaxation of Ventricles • T wave appears in ECG • Ventricles repolarize and relax (begin to expand and fill) • Semilunar valves close (dicrotic notch of aortic pressure curve) - heart sound S2 occurs • AV valves remain closed (not shown) • Ventricles expand but do not fill so there is no change in volume (not shown)