Cardiac beat Prof.Lammers CVS module/Week
The cardiac cycle • The cardiac cycle: the sequence of events from the beginning of one heart beat to the next one. • It is made of: • Systole: the phase of contraction and pumping blood • Diastole: the phase of relaxation and filling
The events during Systole & Diastole • Diastole is made of three main phases: • Early diastole: rapid ventricular filling. • Middle diastole: ventricular filling in slower rate. • Late diastole: contraction of the atrium to pump extra 25% of blood to the ventricles.
The events during systole and Diastole • Systole is made of three phases: • Isovolemic contraction: after filling, AV valve closes & the semilunar valves is still closedpressure raise rapidly in the ventricles. • Ejection: when the pressure in the ventricles is higher than the pressure in the aorta/pulmonary artery semilunar valve openpumping blood out. • Isovolemic relaxation: after blood is pumped, pressure in the ventricles decreases & blood will try to flow back but the atrium pressure is higher than the ventricle AV valves openEARLY DIASTOLE
Pressure-Volume loop • Phase I: ventricular filling volume but pressure is 0 • Phase II: isovolemic contraction volume is constant but the pressure • Phase III: ejection volume decreases and the pressure increases slightly and then decrease • Phase IV: isovolemic relaxation volume is constant but the pressure decreases to 0.
Phase III Phase IV Phase II Phase I
Regulation of the heart • Intrinsic regulation of the heart is by Frank-Starling’s low: Blood volumeStretching of the heartforce of contraction. This is explained by the fact that when the muscle stretchthe actin & myosin filaments are brought to an optimal length degree of integration for force contraction.
Regulation of the heart • Extrinsic regulation of the heart: is by the sympathetic and parasympathetic system. • The sympathetic system: heart rate (+ chronotropic effect) & force of contraction ( + ionotropic effect) • The parasympathetic system (vagus nerve) heart rate and had minimal effect on the force of contraction