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The heart ( Latin cor) is a hollow, muscular organ that pumps blood through the blood vessels by repeated, rhythmic contractions. The term cardiac means "related to the heart", from the Greek cardia for "heart".
In the human body the heart is situated slightly to the left of the middle of the thorax, behind the sternum (breastbone). It is enclosed by a sac known as the pericardium and is surrounded by the lungs. In adults, it weighs about 300~350 g. It consists of four chambers, the two upper atria (singular: atrium) and the two lower ventricles.
A thick, muscular wall, the septum, divides the right atrium and ventricle from the left atrium and ventricle, keeping blood from passing between them. Valves between the atria and ventricles maintain coordinated unidirectional flow of blood from the upper atria to the lower ventricles.
The ventricles are the parts of the heart that pump blood around the body or to the lungs. They are thicker walled than the atria, and the contraction of the ventricle wall is much more important to move blood around.
Anterior (frontal) view of the opened heart. White arrows indicate blood flow. ()
Oxygen-depleted blood from the body enters the right atrium through two veins, the superior vena cava and the inferior vena cavaIn human anatomy, the inferior vena cava is formed by the union of the left and right iliac veins, going up retroperitoneally along the posterior wall of the abdominal cavity, anterior to the vertebrae and to the right of the abdominal aorta to finally em. The blood then passes to the right ventricle. The right ventricle pumps the deoxygenated blood to the lungs, through the pulmonary arteryThe pulmonary arteries carry blood from the heart to the lungs. They are the only arteries (other than umbilical arteries in the fetus) that carry deoxygenated blood. In the human heart, the pulmonary trunk begins at the base of the right ventricle. It is. After the blood loses carbon dioxideCarbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. One of the best known of chemical compounds, it is frequently called by its formula: :CO (pronunciation: "see oh two") Carbon dioxide results from the combustion of organic and picks up oxygenOxygen is the chemical element in the periodic table that has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe. Molecular oxygen (O, often called free oxygen on Earth is thermodynamically un in the lungs, it flows through pulmonary veins to the left atrium. From the left atrium the newly oxygenated blood enters the left ventricle. The left ventricle is the main pumping chamber, sending blood through the aortaAORTA can also mean "always-on real-time access", referring to WAN computer networks. The largest artery in the human body, the aorta originates from the left ventricle of the heart and brings oxygenated blood to all parts of the body in the systemic circ to all of the body except the lungs.
The left ventricle is much thicker than the right because it must pump blood around the entire body, which involves exerting a considerable force to overcome the pressure caused by the body. As the right ventricle must just pump blood to the lungs it requires less muscle.
Even though the ventricles lie below the atria, the two vessels through which the blood exits the heart (the pulmonary artery and the aorta) leave the heart at its top side.
The wall of the heart is very muscular and does not tire. It consists of three distinct layers. The first is the outer epicardiumEpicardium describes the outer layer of heart tissue (from Greek; epi outer, cardium heart)). When considered as a part of the pericardium, it is the inner layer, or visceral pericardium''. Its largest constituent is connective tissue and functions as a p which is composed of a layer of flattened epithelial cells and connective tissue. Beneath this is a much thicker myocardium made up of cardiac muscle. The endocardium is a further layer of flattened epithelial cells and connective tissue.
A large blood supply is necessary to power the heart itself. It is supplied by the left and right coronary arteries, which branch off from the aorta.
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