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The human heart is a muscular, cone-shaped, hollow organ about the size of a fist (about 12cm in length and 9cm in breadth). The heart is situated behind the sternum, between the lungs in the thoracic cavity. The heart is tilted slightly such that its apex is towards the left side.
The major part of the heart is made up of muscles and is called myocardium. The inner lining of the heart is called the endothelium. The heart is covered by a membrane called pericardium. The pericardium encloses the pericardial cavity that houses the heart.
The human heart is four-chambered. The upper chambers are called the atria or the auricles and the lower two chambers are called the ventricles. The two atria are separated by the interatrial septum. The two ventricles are separated from each other by the interventricular septum. The ventricles have more muscular walls than the auricles.
The right side of the heart is concerned with deoxygenated blood and the left side of the heart with the oxygenated blood. The right auricle opens into the lower right ventricle. This opening is guarded by auriculo-ventricular valve (auriculo ventricular valve). This valve is called the tricuspid valve as it has three flaps. The flaps of the valves are connected to the walls of the ventricle by tendons called the chorda tendinae.
The left auricle opens into the lower left ventricle. This opening is guarded by the bicuspid (having two flaps) or the mitral valve. The tricuspid and the bicuspid valves prevent backflow of blood into the auricles from the ventricles when the latter pump the blood into the blood vessels.
The deoxygenated blood from the different parts of the body are collected by the two major veins called the vena cavae - superior vena cava collecting from the upper body and the inferior vena cava collecting from the lower body. The blood from the vena cavae is poured into the right auricle.
The right ventricle opens to a major artery called the pulmonary artery which takes the deoxygenated blood to the lungs. The junction between the pulmonary artery and the right ventricle is guarded by a semilunar valve. This valve prevents the backflow of blood into the ventricle from the artery.
The left auricle receives oxygenated blood from the left and right pulmonary veins coming from the left and right lung respectively. The left ventricle opens into a major artery called the aorta. The junction between the aorta and the left ventricle is also guarded by semilunar valve that prevents backflow of blood from the aorta into the ventricle.
Therefore, the right side of the heart is concerned with the deoxygenated blood and the left side of the heart is concerned with the oxygenated blood. Further, the auricles are the receiving chambers and the ventricles are the pumping chambers. When the ventricles pump blood into the blood vessels, the bicuspid and tricuspid valves prevent the backflow into the auricles.
The function of the heart is to pump blood into the blood vessels to ensure that blood reaches all the parts of the body. This is done by the contraction and relaxation of the chambers of the heart. Contraction is called systole and relaxation is called diastole. The pumping action of heart takes place in a rhythmic pattern.
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