The human heart is roughly as big as a fist. It is protected by the sternum in front, the spine at the back, and the lungs at the sides of it. The tissue layering the heart has three layers. The outermost layer is the Pericardium and it is a double-layered membranous sac filled with fluid.
The outer layer of the Pericardium is attached to the surrounding organs, and the major blood vessels running to the heart. The inner layer is connected to the heart muscle. The middle layer, or the Myocardium, is the actual muscle tissue of the heart. The Myocardium is lined on the inside with the third layer known as Endocardium.
The human heart comprises of four chambers, namely two upper auricle and the two lower ventricles. The left chambers and the right chambers are divided vertically by part of the myocardial heart muscle. The right atrium and the right ventricle are separated by the tricuspid valve. Similarly, the left atrium and the left ventricle are separated by the mitral or bicuspid valve. The valves serve to send the blood in one direction only.
The right atrium has a very thin wall as it serves to receive the deoxygenated blood from the veins while the right ventricle sends the blood it receives from the right auricle to the lungs for oxygenation. The left atrium receives oxygenated blood from the lungs. The left ventricle has the thickest wall as it pumps blood into the aorta, and from there to the rest of the body.
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