A short note of mine regarding : Cardiac cycle
It describe all the activities of the heart through one complete heartbeat.
a contraction event - systole
a relaxation event - diastole
Atrial cycle
1. atrial systole
Duration : 0.1 second
Event :
-Increase in the intra-atrial pressure.
-Increase in the ventricular pressure
-End diastolic volume (EDV) is the amount of blood in ventricle just before systole.
2. Atrial Diastole
Duration : 0.7 second
Event:
-coincide with the ventricular diastole
-atrial muscle relax
-gradual filling of atria due to continuos venous return.
-pressure gradually increase in atria
-drop down to almost 0 with the opening of AV valves.
-then pressure rises again and follow ventricular pressure during rest of atrial diastole.
Ventricular cycle
1. Ventricular systole
a) phase of isovolumic contraction
-ventricular pressure > atrial pressure causing closure of Av valves.
-produces first heart sound
-AV close, semilunar not yet open so ventricle contract as closed chamber
-pressure inside ventricle rise rapidly.
-as ventricle contract , volume of blood in ventricle doesnt change - isovolumic contraction
b) Phase of ventricular ejection
-begin with opening semilunar valves
-can be divide into :
a) rapid ejection phase - where the semilunar valves open, the blood rapidly ejected out. 2/3 of SV is ejected out. so pressure rise in ventricle.
b) slow ejection phase - where no futher ventricular contraction and the pressure starts declining. 1/3 of SV is ejected out.
2. Ventricular diastole
a) protodiastole
-ventricle starts relaxing
-intraventricular pressure fall rapidly.
-elevated pressure in distended arteris immediately pushes blood back toward ventricle causing semilunar valve to close.
-produce 2nd heart sound
b)Isovolumic relaxation phase
-begin with closure of semilunar valves
-semilunar valves close, AV not yet open so ventricle relax as closed chamber that causing rapid fall of pressure inside the ventricle.
-ventricular colume remain constant.
-aortic pressure smoothly declines till 80mmHg, then another ventricular systole boost the aortic pressure again.
c) rapid passive filling
-ventricular systole, atria in diastole -> venous return continues -> atrial pressure increase.
-AV valves open , increase atrial pressure cause a rapid , initial flow of blood into ventricle.
-causing 3rd heart sound
-atria and ventricles pressure decrease as ventricular relaxation occur.
d) Reduced filling and diastasis.
-presssure in atria and ventricles decrease and remain little above 0.
-decrease the rate of blod flow from the atria to ventricle causing a very slow filling -= diastasis.
e)Last rapid filling phase
-coincides with atrial systole.
-atrial systole bring last rapid filling
-pushes the additional 25% of blood in ventricles.
-ventricular cycle is completed.
Hope it helps you guys. Feel free to drop any comments :) Thank you
xo, SuhanaAsyikin