the heart is an organ that has a pump function with each heartbeat there is an increase in pressure in the circulatory system thus causing a pressure difference and guaranteeing blood flow to all organs the cardiac cycle is the sequence of electrical and mechanical events which repeat with each heartbeat this has two main phases syy where the heart muscle contracts and diast where it relaxes the phases of the cardiac cycle happen in the same way in the right and left Chambers but there is a diff
erence in pressures and volumes for practical purposes we are going to explain the cycle in the left cavities in the left ventricle there is a residual volume of approximately 50 mL of blood from the previous cardiac cycle and has a pressure of 2 to 3 mm of mercury initially blood enters from the pulmonary veins to the left atrium filling this cavity until an increase in atrial pressure is generated which exceeds that of The ventricle therefore the atrio ventricular valves open thus initiating t
he so-called ventricular filling sagge or inflow stage when 2/3 of the ventricular filling time has occurred the sinus node generates an electrical impulse which initiates atrial syy which is represented by the p-wave on the electrocardiogram this atrial contraction causes an increase in ventricular pressure while the atrial pressure drops little by little because the atrium is evacuating until finally it empties completely and relaxes for the above the pressure in The ventricle becomes greater
than that in the atrium causing the atrio ventricular valve to close which causes the first noise or S1 this is how the ventricular filling stage ends with an indias volume of approximately 130 ml to remember the ventricular filling stage begins with the opening of the atrio ventricular valves and ends with their closure blood must leave the left ventricle into the systemic circulation and for this to occur The ventricle must overcome the pressure of the aorta so the electrical impulse travels f
rom the sinus node to the atrioventricular node causing ventricular depolarization represented by the QRS complex of the electrocardiogram this is how ventricular syy begins which increases the pressure of The ventricle without changes in volume because the valves are closed for the moment this period is known as the isovolumetric contraction stage when the left ventricle exceeds the pressure of the aorta of approximately 70 mm of mercury it causes the aortic valve to open starting the ejection
stage in which blood begins to flow from the left ventricle to the aorta progressively decreasing ventricular volume but at the same time increasing its pressure to approximately 120 mm of mercury because it continues to contract later comes the moment when the ventricle already has little blood and the strength of the contraction begins to gradually decrease and is repres presented by the t-wave of the electrocardiogram meanwhile the aorta distends and its pressure increases to approximately 12
0 mm of mercury thus equalizing the pressure of The ventricle which is already decreasing progressively causing a retrograde flow and thus the closure of the aortic valve that causes the second sound or S2 thus ending the ventricular ejection phase to remember the isovolumetric contraction stage begins with the closure of the atrio ventricular Valves and ends with the opening of the sem lunar valves and the ejection stage begins with the opening of the semi lunar valves and ends with their closi
ng finally The ventricle stops Contracting and there is an Abrupt drop in pressure returning to the initial 2 to 3 mm of mercury and with approximately 50 mm of blood remaining from each cycle this period is called the isov volumetric relaxation stage which lasts until the new opening of the atrio ventricular valve where a new cycle begins to remember the ISO ometric relaxation stage begins with the closure of the semi lunar valves and ends with the opening of the atrio ventricular [Music] valve
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