10.09.2011

CARDIAC CYCLE

Posted on 12:26 AM by know about heart


It is a sequence of events that occur from the beginning of one heart beat to the beginning of the next. An average 0.8s is required for complete a cycle.
PHASE: Cardiac cycle has two phases
1)   Systolic phase
2)   Diastolic phase
Systolic phase is dividing into two period_
1) ATRIAL SYSTOLE (0.1s)
In atrial systole_
1)   We know that Sino atrial node (SA node) is located in the right atrium. Therefore, it starts the cycle.
2)   Atrial systole drive forwards the blood into ventricle
3)   In atrial systole, atrial muscles are contract; this contraction narrows the great veins.
4)   For inrush of blood into the ventricle, a sound is creating called fourth heart sound
2) VENTRICULAR SYSTOLE (0.3s):
When atrial systole is end this period is start. It has two phases.
A) period of isometric contraction:
1) At the start of ventricular systole, pressure rises suddenly
2) Mitral and tricuspid valves close, semilunar valves are still closed.
3) Pressure is increase in the muscle but there is no restriction of muscle cell.
4) There is no emptying
5) First heart sound creates in this period when AV valves are closed.
B) PERIOD OF EJECTION:
1)When the pressure in the right and left ventricles increase than the pressure in the aorta and pulmonary artery, the semilunar valves open and ejection period begins.

 DIASTOLIC phase is dividing into two periods:
1) ATRIAL DIASTOLE (0.7s):
In atrial diastole, blood is collect by atria from the great veins.
2) VENTRICULAR DIASTOLE (0.5s):
There are several phase________
A)   Protodiastole(0.04s):
Just after the end of the ventricular systole, ventricular diastole begins .Intraventricular pressure fall rapidly. The interval between the onset of the diastole and the closure of semilunar valves is called Protodiastole.

B)    Period of isometric relaxation:
1)   Ventricular volume has no change although ventricular muscles continue to relax. Semilunar valve is closed.
2)   Second heart sound is creating due to close of semilunar valves.
C)    FIRST RAPID FILLING PHASE (0.113s):
1)   Ventricular pressure falls below atrial pressure.
2)   Atrioventricular valves open permitting the ventricle to fill.
3)   Third heart sound is creating.
D)   SLOW FILLING PHASE (0.167):
1)   VENTRICLES are already full to a  large extent.
2)   The pressure of ventricle rise slowly
E) LAST RAPID FILLING PHASE (0.1s):
  1) This phase coincides with the atrial systole.
 2) DUE TO ATRIAL CONTRACTION, blood rushes into the ventricle causing rapid filling.
3) Due to the vibrations initiated by inrush of blood into the ventricles fourth heart sound occurs.



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