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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 .

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cardiac beat

Cardiac beat

Prof.Lammers

CVS module/Week

the cardiac cycle
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
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
The events during systole and Diastole
  • Systole is made of three phases:
    • Isovolemic contraction: after filling, AV valve closes & the semilunar valves is still closedpressure raise rapidly in the ventricles.
    • Ejection: when the pressure in the ventricles is higher than the pressure in the aorta/pulmonary artery semilunar valve openpumping 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 openEARLY DIASTOLE
pressure volume loop
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.
slide9
Phase III

Phase IV

Phase II

Phase I

regulation of the heart
Regulation of the heart
  • Intrinsic regulation of the heart is by Frank-Starling’s low: Blood volumeStretching of the heartforce of contraction.

This is explained by the fact that when the muscle stretchthe actin & myosin filaments are brought to an optimal length degree of integration for force contraction.

regulation of the heart1
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
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