CARDIAC CYCLE
It is the repetitive pattern of the contraction and relaxation of the heart. It is the contraction [systole] and relaxation [diastole] of the myocardium, to maintain and assist blood flow within the heart and to the other parts of the body. It is about 74 beats per minute in a normal being, and for a heart to beat once [cardiac cycle] it takes approximately 0.8 seconds.
There are 3 phases involved in cardiac cycle;
Atrial systole [systole= contraction]
Ventricular systole
Complete cardiac diastole [cardiac= atria and ventricle] [diastole= rest].
To be able to give a detailed description of cardiac cycle you will need to take note of the following;
Meaning [literary meaning of the phase]
Time
Filling
Physiology of Contraction
Atrial systole [atria=both atrim] [systole=contract]
ATRIA SYSTOLE VENTRICULAR SYSTOLE
This is the contraction of both atria [meaning] to force blood into the ventricles, it takes place for about 0.1s [time].
As the superior and inferior venecava fill the right atrium with deoxygenated blood, the right and left pulmonary veins fill the left atrium with oxygenated blood [fillings].
Blood entering the atrium through the superior venacava triggers the SA node to send an impulse of atrial myocardial contraction, which enable the atria to contract, hereby emptying it content through the tricuspid and bicuspid valve into the ventricles below. [physiology of contraction]
Ventricular systole
This is the contraction of both ventricles to force blood into the pulmonary [lungs for oxygenation] and systemic [throughout the body] circulation, it takes place for about 0.3s.
The impulse sent by SA node is delayed for 0.1s before reaching the AV node, which results in contraction of the atria before the ventricles. As the AV node receives the impulse of contraction, it sends it inferiorly to the bundle of HIS, which continues downwards to the apex of the heart through the right and left AV bundle. The impulse is conducted superior-laterally to the level of the ventricles, then the right and left AV bundle together with the purkinje fibres initiate the impulse of ventricular myocardial contraction, hereby forcing the blood into the systemic circulation.
Complete cardiac diastole [diastole=relaxation]
This is the relaxation of the heart after series of contraction [atrial and ventricular contraction]. It takes place for about 0.4 seconds,and the heart prepares for another cycle.