Blood Flow Through Heart
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Cardiac Cycle: A Comprehensive Guide to Heart Function, Study notes of Medical Sciences
A detailed explanation of the cardiac cycle, the sequence of events that occur during a single heartbeat. It covers the phases of atrial and ventricular systole and diastole, including isovolumetric contraction and relaxation, rapid ejection and filling, and reduced ejection and filling. The document also discusses pressure changes in the heart chambers and blood vessels during the cardiac cycle, as well as the heart sounds produced by valve closure. This comprehensive guide is an excellent resource for understanding the mechanics of heart function.
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2024/2025
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Blood Flow Through Heart
CARDIAC CYCLE
- (^) The normal duration of the cardiac cycle is 0.8 second.
- (^) Each beat of the heart consists of systole and diastole of atria and ventricles.
- (^) Systole is the contraction of the heart during which blood is ejected out from the heart
- (^) Diastole is the relaxation of the heart during which the chambers of the heart are filled with blood
END DIASTOLIC VOLUME 110 - 120 ml STROKE VOLUME 70 ml END SYSTOLIC VOLUME 40 - 50 ml SV = EDV-ESV DURATION OF CARDIAC CYCLE α 1 HR
The normal duration of the cardiac cycle is 0.8 sec. ATRIAL EVENTS:
- (^) Atrial Systole - 0.1 sec
- (^) Atrial Diastole - 0.7 sec VENTRICULAR EVENTS:
- (^) Ventricular systole - 0.3 sec
- (^) Ventricular diastole - 0.5 sec
- (^) Ventricular Systole: 1. Isovolumetric contraction phase - 0.05 sec 2. Rapid Ejection phase - 0.10 sec 3. Reduced Ejection phase - 0.15 sec
Events in the cardiac cycle
- (^) Initially, during diastole, all the four chambers of the heart ie both atria and ventricles are relaxed and filled with blood due to venous return.
ATRIAL SYSTOLE
The end of
diastole
- (^) Atrial systole: 0. sec.
- (^) Atrial pressure rises.
- (^) Right atrial : 4- mmHg
- (^) Left atrial : 7- mmHg
ISOVOLUMETRIC CONTRACTION The Beginning of systole After the ventricles have filled by atrial contraction, AV (Atrio- ventricular) valves close as the ventricles begin their contraction and intraventricular pressure increases. The semilunar valves remain closed and this makes ventricle a closed cavity. The volume in the ventricles remains unchanged throughout the contraction, hence the name isovolumetric. Closure of the AV valves in this phase causes the first heart sound.
RAPID EJECTION The semilunar valves
(aortic and pulmonary) open at the beginning of this phase. 2/ rd of stroke volume ejected Aortic pressure increases but slightly less than ventricles
PROTODIASTOLIC PHASE
- (^) When ventricles begin to relax, the AV valves close and the semilunar valves remain open.
- (^) As the intra ventricular pressure decreases below the pressure in the aorta and pulmonary artery, the blood tries to come back into the ventricles.
- (^) This is prevented by closure of semilunar valve which produces the
ISOVOLUMETRIC RELAXATION The beginning of Diastole In this phase, the ventricle is in a closed cavity, which is relaxing During this phase the intra ventricular pressure goes below the atrial pressure.