The Pericardium
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The pericardium is a fibro-serous sac that contains the heart and the roots of the great vessels (Gray, 1918). In front it is separated from the anterior wall of the thorax for the most part, but a small area corresponding with the left half of the lower portion of the body of the sternum and the medial ends of the cartilages of the fourth and fifth ribs on the left side, comes in contact with the chest wall. In childhood, the lower extremity of the thymus is in contact with the front upper part of the pericardium. Posteriorly, the pericardium rests on the bronchi, esophagus, descending thoracic aorta, and the posterior part of the mediastinal surface of each lung. Laterally it is covered by the pleurae in relation with the mediastinal surfaces of the lung. The pericardium derives its arteries from the internal mammary and its musculophrenic branch, and from the descending thoracic aorta. Its nerve supply is derived from the vagus and phrenic nerves, and the sympathetic trunks. The pericardium consists of two sacs intimately connected with each other, but different in structure (Gray, 1918). The outer sac is known as the fibrous pericardium, and consists of fibrous tissue. It forms a flask-shaped bag, whose neck is closed by fusion with the external coats of the great vessels, and is continuous with the pretracheal layer of the deep cervical fascia. Its base is attached to the central tendon and muscular fibers of the left side of the diaphragm. It is attached
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pumped into the pulmonary arteries through the semilunar valves. The pulmonary valve prevents the blood from flowing back into the right ventricle. The pulmonary artery carries the drop of blood to the lungs, where it releases carbon dioxide and picks up oxygen. It is then returned to the heart by the pulmonary veins. The semilunar valves close and the atrioventricular valves open, and the drop of blood travels from the pulmonary vein into the left atrium. This circuit is the pulmonary circuit.
3.3 The coronary arteries regulate the blood supply to the heart muscle depending on the oxygen needs of the heart, which is determined by the heart rate, blood pressure, force of the heart's contraction, and thickness of the heart muscle (Reid, 2003). The harder the heart works, the more oxygen it needs. For example, exercise increases heart rate and blood pressure, and therefore oxygen need. The main way to increase the oxygen supply to the heart is to increase the blood flow through the coronary arteries. This is done by dilating the coronary arteries. When the heart contracts, the coronary arteries contract, and coronary blood flow is decreased. When the heart relaxes, the coronary arteries dilate and more blood can flow
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Some common words found in the essay are:
, References Bailey, coronary arteries, left ventricle, atrioventricular valves, coronary artery, left atrium, blood flowing, serous pericardium, valve prevents, blood flow, semilunar valves, inferior vena cava, valve prevents blood, prevents blood flowing, oxygenated blood flowing, blood flowing left,
Approximate Word count = 1251
Approximate Pages = 5 (250 words per page)
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