Anatomy & Physiology: The Unity of Form and Function, 7th Edition

Published by McGraw-Hill Education
ISBN 10: 0073403717
ISBN 13: 978-0-07340-371-7

Chapter 19 - Section 19.5 - Blood Flow, Heart Sounds, and the Cardiac Cycle - Before You Go On - Page 734: 22

Answer

The **isovolumetric phases** of the cardiac cycle are periods during which the volume of blood in a particular chamber of the heart remains constant, despite changes in pressure. These phases occur when a heart chamber is contracting or relaxing, but its associated valve(s) are closed, preventing blood from entering or leaving the chamber. In other words, the term "isovolumetric" signifies that the volume remains the same ("iso" means same, and "volumetric" refers to volume). There are two main isovolumetric phases in the cardiac cycle: 1. **Isovolumetric Contraction:** - Occurs in: Both ventricles - Description: During the early phase of ventricular systole (contraction), the ventricles contract and generate pressure, causing the pressure in the ventricles to rise. However, the semilunar valves (aortic and pulmonary valves) are still closed, preventing blood from being ejected into the arteries. Since no blood is leaving the ventricles, the volume remains constant. - Significance: Isovolumetric contraction allows the ventricles to build up sufficient pressure to overcome the pressure in the arteries and open the semilunar valves for ejection. 2. **Isovolumetric Relaxation:** - Occurs in: Both ventricles - Description: During the early phase of ventricular diastole (relaxation), the ventricles start relaxing, causing the pressure inside them to decrease. However, the atrioventricular (AV) valves (mitral and tricuspid valves) are still closed, preventing blood from flowing back into the ventricles from the atria. As a result, the volume of blood within the ventricles remains unchanged. - Significance: Isovolumetric relaxation allows the ventricles to relax and reduces their pressure, which helps close the semilunar valves (aortic and pulmonary valves) that were open during systole. These isovolumetric phases are important for maintaining efficient blood flow and preventing backflow of blood. They play a role in the generation of the characteristic heart sounds (S1 and S2) and contribute to the proper functioning of the heart's pumping action. The closure of the valves during isovolumetric phases ensures unidirectional blood flow and prevents regurgitation of blood into the chambers.

Work Step by Step

The **isovolumetric phases** of the cardiac cycle are periods during which the volume of blood in a particular chamber of the heart remains constant, despite changes in pressure. These phases occur when a heart chamber is contracting or relaxing, but its associated valve(s) are closed, preventing blood from entering or leaving the chamber. In other words, the term "isovolumetric" signifies that the volume remains the same ("iso" means same, and "volumetric" refers to volume). There are two main isovolumetric phases in the cardiac cycle: 1. **Isovolumetric Contraction:** - Occurs in: Both ventricles - Description: During the early phase of ventricular systole (contraction), the ventricles contract and generate pressure, causing the pressure in the ventricles to rise. However, the semilunar valves (aortic and pulmonary valves) are still closed, preventing blood from being ejected into the arteries. Since no blood is leaving the ventricles, the volume remains constant. - Significance: Isovolumetric contraction allows the ventricles to build up sufficient pressure to overcome the pressure in the arteries and open the semilunar valves for ejection. 2. **Isovolumetric Relaxation:** - Occurs in: Both ventricles - Description: During the early phase of ventricular diastole (relaxation), the ventricles start relaxing, causing the pressure inside them to decrease. However, the atrioventricular (AV) valves (mitral and tricuspid valves) are still closed, preventing blood from flowing back into the ventricles from the atria. As a result, the volume of blood within the ventricles remains unchanged. - Significance: Isovolumetric relaxation allows the ventricles to relax and reduces their pressure, which helps close the semilunar valves (aortic and pulmonary valves) that were open during systole. These isovolumetric phases are important for maintaining efficient blood flow and preventing backflow of blood. They play a role in the generation of the characteristic heart sounds (S1 and S2) and contribute to the proper functioning of the heart's pumping action. The closure of the valves during isovolumetric phases ensures unidirectional blood flow and prevents regurgitation of blood into the chambers.
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