Chapter 19 - Section 19.4 - Study Guide - Assess Your Learning Outcomes - Page 740: 1

"Systole" and "diastole" are terms used to describe the two phases of the cardiac cycle, which is the sequence of events that occur during each heartbeat. These phases are essential for the heart's pumping action and the circulation of blood throughout the body. Here are the meanings of systole and diastole: **1. Systole:** Systole refers to the phase of the cardiac cycle during which the heart muscle contracts, leading to the ejection of blood from the heart chambers. Specifically: - **Atrial Systole:** During atrial systole, the atria contract, pushing blood into the ventricles. This phase is relatively brief and occurs just before the ventricles begin to contract. - **Ventricular Systole:** During ventricular systole, the ventricles contract forcefully. The pressure within the ventricles rises, causing the atrioventricular valves (tricuspid and mitral valves) to close, preventing backflow of blood into the atria. The semilunar valves (pulmonary and aortic valves) open, allowing blood to be ejected into the pulmonary artery and aorta, respectively. **2. Diastole:** Diastole refers to the phase of the cardiac cycle during which the heart muscle relaxes and chambers fill with blood. Specifically: - **Atrial Diastole:** During atrial diastole, the atria are relaxed and are in the process of filling with blood from the veins. Blood flows passively from the superior and inferior vena cava into the right atrium, and from the pulmonary veins into the left atrium. - **Ventricular Diastole:** During ventricular diastole, the ventricles are relaxed. The semilunar valves (pulmonary and aortic valves) close to prevent backflow from the pulmonary artery and aorta into the ventricles. The atrioventricular valves (tricuspid and mitral valves) open as the ventricles expand, allowing blood to flow from the atria into the ventricles. In summary, systole is the phase of the cardiac cycle when the heart contracts, and blood is ejected from the chambers. Diastole is the phase when the heart relaxes, and chambers fill with blood. These alternating phases are vital for maintaining the heart's pumping function and ensuring efficient blood circulation throughout the body.

"Systole" and "diastole" are terms used to describe the two phases of the cardiac cycle, which is the sequence of events that occur during each heartbeat. These phases are essential for the heart's pumping action and the circulation of blood throughout the body. Here are the meanings of systole and diastole: **1. Systole:** Systole refers to the phase of the cardiac cycle during which the heart muscle contracts, leading to the ejection of blood from the heart chambers. Specifically: - **Atrial Systole:** During atrial systole, the atria contract, pushing blood into the ventricles. This phase is relatively brief and occurs just before the ventricles begin to contract. - **Ventricular Systole:** During ventricular systole, the ventricles contract forcefully. The pressure within the ventricles rises, causing the atrioventricular valves (tricuspid and mitral valves) to close, preventing backflow of blood into the atria. The semilunar valves (pulmonary and aortic valves) open, allowing blood to be ejected into the pulmonary artery and aorta, respectively. **2. Diastole:** Diastole refers to the phase of the cardiac cycle during which the heart muscle relaxes and chambers fill with blood. Specifically: - **Atrial Diastole:** During atrial diastole, the atria are relaxed and are in the process of filling with blood from the veins. Blood flows passively from the superior and inferior vena cava into the right atrium, and from the pulmonary veins into the left atrium. - **Ventricular Diastole:** During ventricular diastole, the ventricles are relaxed. The semilunar valves (pulmonary and aortic valves) close to prevent backflow from the pulmonary artery and aorta into the ventricles. The atrioventricular valves (tricuspid and mitral valves) open as the ventricles expand, allowing blood to flow from the atria into the ventricles. In summary, systole is the phase of the cardiac cycle when the heart contracts, and blood is ejected from the chambers. Diastole is the phase when the heart relaxes, and chambers fill with blood. These alternating phases are vital for maintaining the heart's pumping function and ensuring efficient blood circulation throughout the body.