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Smart Art Video: Cardiac Cycle

Pearson
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>> Welcome to another Anatomy and Physiology SmartArt Video, where we guide you through an important piece of art. After watching this video, you should be able to explain the events of the cardiac cycle. Diagramed here is a single cardiac cycle, which lasts about 800 milliseconds, or 8/10 of a second. Let's begin here at the red arrow labeled start. In this first image of the heart, all four heart chambers are relaxed, therefore, in diastole, and partially filled with blood. Atrial systole, also known as contraction, begins and complete ventricular filling. Notice the green arrows show the atria contract, and the black arrows indicate blood flowing into the ventricles. Atrial diastole follows and continues until the next cardiac cycle begins. Ventricular systole now begins and is a process divided into two phases. The first phase, shown in this figure is isovolumetric contraction. It is called isovolumetric because the volume of blood within the ventricles does not change. During this initial phase, ventricular contraction closes the atrioventricular or AV valves. The second phase is ventricular ejection. When the ventricular pressure finally exceeds the pressure in the arteries, then that pressure increase opens both the aortic and pulmonary semilunar valves. Blood now exits the ventricles and is forced into the aorta and pulmonary trunk. Here in early ventricular diastole, blood flows backward towards the ventricles as ventricular pressure rapidly drops. This backflow of blood against the semi lunar valves causes them to close. At this time, blood is also flowing into the relaxed atria. Notice here, the AV valves are still closed. This phase is called isovolumetric relaxation. Finally, in late ventricular diastole, all chambers are relaxed and filling passively to about 70% of their capacity. To summarize, a single cardiac cycle includes atrial systole, when both atria contract at the same time to complete ventricular filling, followed by ventricular systole. Isovolumetric contraction is the first phase of ventricular systole and causes the AV valves to close, while the second phase is ventricular ejection, which opens the semilunar valve as blood is forced into the arteries. As blood pressure rapidly drops in ventricular diastole, the semilunar valves close and the ventricles begin to fill again as all four chambers of the heart rest and passively fill prior to the next cardiac cycle. So what? Why is it important to understand the events of a normal cardiac cycle? Well, this is crucial to understanding many serious heart conditions. For example, suppose a patient has a myocardial infarction, also known as a heart attack, that has seriously weakened the left ventricle. Left ventricular ejection will decrease. Blood flow will back up between the left and right sides of the heart, resulting in congestion in the lungs. The resulting respiratory complications can be life-threatening. And to understand the many congenital defects of the heart, it's important to grasp the normal cardiac cycle, as these cardiac abnormalities interfere with normal blood flow and valve function.
>> Welcome to another Anatomy and Physiology SmartArt Video, where we guide you through an important piece of art. After watching this video, you should be able to explain the events of the cardiac cycle. Diagramed here is a single cardiac cycle, which lasts about 800 milliseconds, or 8/10 of a second. Let's begin here at the red arrow labeled start. In this first image of the heart, all four heart chambers are relaxed, therefore, in diastole, and partially filled with blood. Atrial systole, also known as contraction, begins and complete ventricular filling. Notice the green arrows show the atria contract, and the black arrows indicate blood flowing into the ventricles. Atrial diastole follows and continues until the next cardiac cycle begins. Ventricular systole now begins and is a process divided into two phases. The first phase, shown in this figure is isovolumetric contraction. It is called isovolumetric because the volume of blood within the ventricles does not change. During this initial phase, ventricular contraction closes the atrioventricular or AV valves. The second phase is ventricular ejection. When the ventricular pressure finally exceeds the pressure in the arteries, then that pressure increase opens both the aortic and pulmonary semilunar valves. Blood now exits the ventricles and is forced into the aorta and pulmonary trunk. Here in early ventricular diastole, blood flows backward towards the ventricles as ventricular pressure rapidly drops. This backflow of blood against the semi lunar valves causes them to close. At this time, blood is also flowing into the relaxed atria. Notice here, the AV valves are still closed. This phase is called isovolumetric relaxation. Finally, in late ventricular diastole, all chambers are relaxed and filling passively to about 70% of their capacity. To summarize, a single cardiac cycle includes atrial systole, when both atria contract at the same time to complete ventricular filling, followed by ventricular systole. Isovolumetric contraction is the first phase of ventricular systole and causes the AV valves to close, while the second phase is ventricular ejection, which opens the semilunar valve as blood is forced into the arteries. As blood pressure rapidly drops in ventricular diastole, the semilunar valves close and the ventricles begin to fill again as all four chambers of the heart rest and passively fill prior to the next cardiac cycle. So what? Why is it important to understand the events of a normal cardiac cycle? Well, this is crucial to understanding many serious heart conditions. For example, suppose a patient has a myocardial infarction, also known as a heart attack, that has seriously weakened the left ventricle. Left ventricular ejection will decrease. Blood flow will back up between the left and right sides of the heart, resulting in congestion in the lungs. The resulting respiratory complications can be life-threatening. And to understand the many congenital defects of the heart, it's important to grasp the normal cardiac cycle, as these cardiac abnormalities interfere with normal blood flow and valve function.