The left AV valve- the bicuspid or mitral valve, consists of two flaps, or cusps, of endocardium. Atrioventricular or AV valves are located between the atrial and ventricular chambers on each side, and they prevent backflow into the atria when the ventricles contract. The heart is equipped with four valves, which allow blood to flow in only one direction through the heart chambers. Blood returned to the left side of the heart is pumped out of the heart into the aorta from which the systemic arteries branch to supply essentially all body tissues. Oxygen-rich blood drains from the lungs and is returned to the left side of the heart through the four pulmonary veins.
The pulmonary trunk splits into the right and left pulmonary arteries, which carry blood to the lungs, where oxygen is picked up and carbon dioxide is unloaded.
The heart receives relatively oxygen-poor blood from the veins of the body through the large superior and inferior vena cava and pumps it through the pulmonary trunk. The great blood vessels provide a pathway for the entire cardiac circulation to proceed. The septum that divides the heart longitudinally is referred to as either the interventricular septum or the interatrial septum, depending on which chamber it separates. The two inferior, thick-walled ventricles are the discharging chambers, or actual pumps of the heart wherein when they contract, blood is propelled out of the heart and into the circulation. The two superior atria are primarily the receiving chambers, they play a lighter role in the pumping activity of the heart. The heart has four hollow chambers, or cavities: two atria and two ventricles. The endocardium is the innermost layer of the heart and is a thin, glistening sheet of endothelium hat lines the heart chambers. The myocardium consists of thick bundles of cardiac muscle twisted and whirled into ringlike arrangements and it is the layer that actually contracts. The epicardium or the visceral and outermost layer is actually a part of the heart wall. The heart muscle has three layers and they are as follows: Deep to the fibrous pericardium is the slippery, two-layer serous pericardium, where its parietal layer lines the interior of the fibrous pericardium. The loosely fitting superficial part of this sac is referred to as the fibrous pericardium, which helps protect the heart and anchors it to surrounding structures such as the diaphragm and sternum. The heart is enclosed in a double-walled sac called the pericardium and is the outermost layer of the heart. Its broad posterosuperior aspect, or base, from which the great vessels of the body emerge, points toward the right shoulder and lies beneath the second rib. It’s more pointed apex is directed toward the left hip and rests on the diaphragm, approximately at the level of the fifth intercostal space. Snugly enclosed within the inferior mediastinum, the medial cavity of the thorax, the heart is flanked on each side by the lungs. Approximately the size of a person’s fist, the hollow, cone-shaped heart weighs less than a pound. The modest size and weight of the heart give few hints of its incredible strength. The cardiovascular system can be compared to a muscular pump equipped with one-way valves and a system of large and small plumbing tubes within which the blood travels. The heart separates the pulmonary and systemic circulations, which ensures the flow of oxygenated blood to tissues. The valves of the heart secure a one-way blood flow through the heart and blood vessels. Contractions of the heart produce blood pressure, which is needed for blood flow through the blood vessels. Variations in the rate and force of heart contraction match blood flow to the changing metabolic needs of the tissues during rest, exercise, and changes in body position. The functions of the heart are as follows: Capillary Exchange of Gases and Nutrients.Intrinsic Conduction System of the Heart.Major Veins of the Systemic Circulation.Major Arteries of the Systemic Circulation.
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