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Cardiac Cycle

Pearson
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The three phases of the cardiac cycle are: Ventricular filling, which occurs during mid-to-late diastole. Ventricular systole, which includes isovolumetric contraction and ventricular ejection and isovolumetric relaxation, which occurs during early diastole. The next several screens will show these phases in more detail. Here is an anterior view. Here’s the left side of the heart. Let’s watch when a syringe injects dye iinto the superior and inferior vena cava to show blood flow on right side of heart. The first phase of the cardiac cycle is ventricular filling, which occurs during mid-to-late diastole when the heart chambers are relaxed. Blood flows passively into the atria, then through the open AV valves, and then continues into the ventricles, where the pressure is lower. Let’s watch the atrial contract, forcing the remaining blood into the ventricles. This will demonstrate blood flow on the right side of the heart, but remember that blood is moving through both sides of the heart at the same time. The second phase of the cardiac cycle is ventricular systole. As the ventricles contract, intraventricular pressure rises, closing the AV valves. The brief period during which the ventricles are completely closed chambers is the isovolumetric contraction phase. The ventricular ejection phase begins when rising ventricular pressure forces the semilunar valves open. Blood is then ejected from the heart into the pulmonary trunk and aorta. In the third phase of the cardiac cycle, isovolumetric relaxation, the ventricles relax and ventricular pressure drops. Blood in the aorta and pulmonary trunk backflows toward the heart, closing the semilunar valves. The ventricles are totally closed off again in this isovolumetric relaxation phase. Meanwhile, the atria have been filling with blood. When the pressure exerted by blood on the atrial side of the AV valves exceeds that in the ventricles below, the AV valves are forced open and the ventricular filling phase begins again.
The three phases of the cardiac cycle are: Ventricular filling, which occurs during mid-to-late diastole. Ventricular systole, which includes isovolumetric contraction and ventricular ejection and isovolumetric relaxation, which occurs during early diastole. The next several screens will show these phases in more detail. Here is an anterior view. Here’s the left side of the heart. Let’s watch when a syringe injects dye iinto the superior and inferior vena cava to show blood flow on right side of heart. The first phase of the cardiac cycle is ventricular filling, which occurs during mid-to-late diastole when the heart chambers are relaxed. Blood flows passively into the atria, then through the open AV valves, and then continues into the ventricles, where the pressure is lower. Let’s watch the atrial contract, forcing the remaining blood into the ventricles. This will demonstrate blood flow on the right side of the heart, but remember that blood is moving through both sides of the heart at the same time. The second phase of the cardiac cycle is ventricular systole. As the ventricles contract, intraventricular pressure rises, closing the AV valves. The brief period during which the ventricles are completely closed chambers is the isovolumetric contraction phase. The ventricular ejection phase begins when rising ventricular pressure forces the semilunar valves open. Blood is then ejected from the heart into the pulmonary trunk and aorta. In the third phase of the cardiac cycle, isovolumetric relaxation, the ventricles relax and ventricular pressure drops. Blood in the aorta and pulmonary trunk backflows toward the heart, closing the semilunar valves. The ventricles are totally closed off again in this isovolumetric relaxation phase. Meanwhile, the atria have been filling with blood. When the pressure exerted by blood on the atrial side of the AV valves exceeds that in the ventricles below, the AV valves are forced open and the ventricular filling phase begins again.