The heart consists of four chambers through which blood inconsistent flows. They are divided by heart walls that are made of cardiac muscle as the whole structure. The upper compartments are called atria (singular: atrium), and the lower ones are ventricles. Atlas of Human Cardiac Anatomy interactively shows that the right atrium contains the sinusoidal node, which is vital for the heart’s electrical conduction. The tricuspid valve connects the right atrium with the right ventricle. A similar function is carried out by the mitral valve, which bridges the left atrium to the left ventricle. Semilunar valves are leading the blood from ventricles to blood ways. There are also more helpful diagrams and animations in the named resource that give detailed and up-to-date information.
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The electrical conduction system of the heart
The electrical conduction starts from the sinoatrial node, which is sometimes called a pacemaker for its functions. The propagation of the electrical activity across the atrial muscle fibers brings uniform atrial contraction. The action potential travels down to the atrioventricular node, projecting further to the Bundle of His. The latter is located in the aforementioned heart wall between two ventricles. Conduction of the electrical signal to Purkinje fibers results in ventricular contraction, in other words, systole. The video and overview by Chen and the A.D.A.M. Editorial team provide a concise and useful description of the named mechanism. Electrical activity can be checked by taking an electrocardiogram from the patients.
Blood flow through the heart
The vena cava carries the blood from body tissues and brings it to the right atrium. As it fills with blood, the sinoatrial node fires the action potential, causing the contraction. It results in the opening of the tricuspid valve, which brings the blood to the right ventricle. The high level of pressure inside the ventricle closes the tricuspid valve preventing the flow of the blood in a backward direction. Ventricular systole pumps the blood to the pulmonary circuit, after passing which blood flows to the left atrium. As accessibly pictured in the diagram of 18.7G: Blood Flow in the Heart by Medicine Libretexts, the analogous algorithm is accomplished in the left half of the heart, but the blood is sent to the body tissues. The blood flow through the heart is closely related to its proceeding through body vessels.
Blood flow through the body
Leaving the right ventricle, the deoxygenated blood enters the pulmonary artery, which leads it to the lungs. The closer the blood gets to the lungs, the narrower the vessels become, transforming to arterioles and capillaries. As oxygen diffuses to blood replacing carbon dioxide, a saturated liquid is passed through venioles towards the pulmonary vein fused with the left atrium. Afterward, blood leaves the heart from the left ventricle and flows through the main body artery – artery, which leads it to smaller blood vessels directing to all body tissues. The process has only a single direction, which is explicitly depicted in the animation by Pearson Education called Pathway of Blood through the Pulmonary and Systemic Circuits. The uniformity prevents disruptions and allows blood to flow to all organs.
The cardiac cycle
The cardiac cycle is divided into two phases: diastolic and systolic. The electrocardiogram, pressure readings, and heart sound altogether assist in understanding the cardiac cycle the most (Chambers et al. 118). During the diastolic interval, the atria are filled with blood, and as the atrioventricular valves remain open, the ventricles are slowly filled with blood. Atrial contraction attributes to the P wave in the electrocardiogram and results in the fast filling of ventricles. As the action potential is transmitted through Purkinje fibers and ventricular muscles, the systole starts. The pressure in the aorta raises significantly because of the large amount of blood passing to the blood vessel.
Atlas of Human Cardiac Anatomy. U of Minnesota, 2020. Web.
Chambers, David, et al. “Cardiac cycle.” Basic Physiology for Anaesthetists, Cambridge University Press, 2015, pp. 117-119.
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Chen, Michael A. “Cardiac conduction system.” Medline Plus, 2020. Web.
“18.7G: Blood Flow in the Heart.” Medicine Libretexts, 2020. Web.
“Pathway of Blood through the Pulmonary and Systemic Circuits.” Pearson Education, 2020. Web.