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The Cardiac Cycle.

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The Cardiac Cycle that is the sequence of events that makes up one heartbeat. The heart beats approximately 70 times a minute and is constant it pumps around 75cm3 from each ventricle beat. The cardiac muscle contracts on its own without a nerve impulse this mean it is Myogenic. Contractions commence within the heart by the SAN Sino-atrial node (pacemaker) found in the right atrium. This tissue acts as a clock and contracts spontaneously and rhythmically once a second. When the cardiac muscle contracts the volume in the chamber decrease and the pressure in the chamber increases so the blood is pushed out. The periods of contraction are called Systole. The periods of relaxation are called Diastole. ...read more.


They have semilunar valves that prevent backflow so the blood from the atria does not go back into the pulmonary veins or venae cavae. At 0.1 seconds after the atria has contracted Ventricular Systole happens where the ventricles contract. The thick muscular walls squeeze inwards on the blood increasing the pressure and pushing it out of the heart. When the pressure becomes bigger than the pressure in the atria it pushes the atrio-ventricular valves shut. Preventing the back flow of blood into the atria. Instead blood goes to the aorta and the pulmonary artery opening the semilunar valves in the vessel as it happens. Ventricular Diastole-lasts about 0.3 seconds the muscle relaxes and then the pressure in the ventricles drop. ...read more.


A little amount of the blood trickles down into the ventricles and through the atrio- ventricular valves. The atrial muscle contracts to push blood forcefully down into the ventricles then repeats the cycle again. Normally, the electrical impulse moves through the heart's conduction system, and the heart contracts. Each contraction represents one heartbeat. The atria contract a fraction of a second before the ventricles so the blood empties into the ventricles before the ventricles contract. * Under some conditions, almost all heart tissue is capable of starting a heartbeat, or becoming the "pacemaker," just like the sinus node. An arrhythmia (abnormal heartbeat) may occur when: The heart's natural pacemaker (the sinus node) develops an abnormal rate or rhythm. * The normal conduction pathway is interrupted. Another part of the heart takes over as pacemaker. Gifty Ayanful Cardiac Cycle ...read more.

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