PHASES OF HEART BEAT || CARDIAC CYCLE || CONDUCTING SYSTEM OF HEART || SA NODE AND AV NODE 11 CLASS

#cardiaccycle #PHASESOFHEARTBEAT #heartbeat #cardiaccycle #sanatandharma #avnode #purkinjifibres #depolarization #heartmusclecontraction #delayinavnode #bundleofhus #bundleofhis notes The cardiac cycle is the sequence of events that occur during one complete heartbeat, involving the contraction and relaxation of the heart chambers. It consists of two main phases: diastole and systole. 1. Diastole: This is the relaxation phase of the cardiac cycle when the heart chambers fill with blood. During diastole, the atria and ventricles are in a relaxed state, and blood flows passively from the veins into the atria. The atrioventricular (AV) valves (tricuspid and mitral valves) are open, allowing blood to pass from the atria to the ventricles. At the same time, the semilunar valves (pulmonary and aortic valves) are closed to prevent backflow of blood from the arteries into the ventricles. During this phase, the heart muscles also receive oxygen and nutrients from the coronary arteries. 2. Atrial Systole: Atrial systole is a brief contraction of the atria that occurs towards the end of diastole. This contraction helps to push the remaining blood from the atria into the ventricles. 3. Ventricular Systole: This is the contraction phase of the cardiac cycle when the ventricles forcefully pump blood out of the heart. The ventricles contract, causing an increase in pressure, which closes the AV valves to prevent blood from flowing back into the atria (first heart sound, "lub"). Meanwhile, the pressure opens the semilunar valves, allowing blood to be ejected into the pulmonary artery and aorta. The ventricles then relax briefly (isovolumetric relaxation) before the next cycle begins. The cardiac cycle is regulated and coordinated by the heart's conducting system, a network of specialized cardiac muscle cells that generate and propagate electrical impulses. This system ensures that the heart chambers contract in a coordinated manner, allowing efficient pumping of blood. The main components of the heart's conducting system are: 1. Sinoatrial (SA) Node: Located in the right atrium, the SA node is often referred to as the "pacemaker" of the heart. It generates electrical impulses that initiate each heartbeat. The impulses spread through the atria, causing them to contract and push blood into the ventricles. 2. Atrioventricular (AV) Node: The electrical signals from the SA node reach the AV node, which is located at the junction between the atria and ventricles. The AV node delays the impulse slightly, allowing the atria to complete their contraction before the signal is passed to the ventricles. 3. Bundle of His: After passing through the AV node, the electrical signal travels down the Bundle of His, a bundle of specialized fibers that divides into left and right bundle branches. 4. Purkinje Fibers: The bundle branches further divide into smaller Purkinje fibers, which spread the electrical impulse throughout the ventricles, causing their synchronous contraction. The coordinated action of the heart's conducting system ensures that the atria and ventricles contract and relax at the appropriate time, maintaining an effective pumping rhythm and facilitating proper blood circulation throughout the body.