Answer:
The heart beat sequence is the sequence of events that occurs when the heart beats. As the heart beats, blood circulates through the pulmonary and systemic circuits of the body. There are two stages of the heart beat cycle: the diastole phase and the systole phase. In the diastole phase, the ventricles of the heart relax and the heart fills with blood. In the systole phase, the ventricles contract and pump blood from the heart to the arteries. A cardiac cycle is completed when the chambers of the heart fill with blood and blood from the heart is pumped.
Explanation:
Phases of the cardiac cycle
The cardiac cycle events described below trace the path of blood from the moment it enters the heart to the moment it is pumped from the heart to the rest of the body. The periods of contraction and pumping are systole and the periods of relaxation and filling are diastole. The atria and ventricles of the heart pass through the diastole and systole phases, and the diastole and systole phases occur simultaneously.
1. Ventricular Diastole
For the period of ventricular diastole, the atria and ventricles of the heart are relaxed and the atrioventricular valves are open. The oxygen-free blood that returns to the heart from the body after the last cardiac cycle passes through the superior and inferior cava veins and flows into the right atrium.
Open atrioventricular valves (tricuspid and mitral) allow blood to pass through the atria into the ventricles. The impulses of the sinoatrial node (SA) travel to the atrioventricular node (AV) and the AV node sends a signal that triggers the contraction of both atria. As per a result of this reduction, the right atrium empties its contents into the right ventricle. The tricuspid valve, located between the right atrium and the right ventricle, prevents blood from flowing into the right atrium.
2. Ventricular Systole
At the beginning of the ventricular systole period, the right ventricle, which is full of blood that passes from the right atrium, receives impulses from the fiber branches (Purkinje fibers) that carry electrical impulses that cause it to contract. When this occurs, the atrioventricular valves close and the semilunar valves (pulmonary and aortic valves) open.
Ventricular contraction causes oxygen depleted blood from the right ventricle to be pumped into the pulmonary artery. The pulmonary valve prevents blood from returning to the right ventricle. The pulmonary artery carries deoxygenated blood along the pulmonary circuit to the lungs. Here, the plasma gathers oxygen and returns to the left atrium of the heart through the pulmonary veins.
3. Atrial Diastole
In the period of atrial diastole, semilunar valves close and atrioventricular valves open. Oxygenated blood from the pulmonary veins fills the left atrium, while blood from the vena cava fills the right atrium. The SA node contracts again, causing both atria to do the same.
In this step, the atrial contraction origins the left atrium to empty its contents into the left ventricle and the right atrium to empty its contents into the right ventricle. The mitral valve, located between the left atrium and the left ventricle, prevents oxygenated blood from returning to the left atrium.
4. Atrial Systole
During the period of atrial systole, the atrioventricular valves close and the semilunar valves open. The ventricles receive impulses to contract. Oxygenated blood in the left ventricle is pumped into the aorta and the aortic valve prevents oxygenated blood from returning to the left ventricle. The oxygen-depleted blood is also pumped from the right ventricle to the pulmonary artery at this time.
The aorta branches to provide oxygenated blood to all parts of the body through systemic circulation. After its journey through the body, deoxygenated blood returns to the heart through the vena cava.
