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Pulmonary circulation is the portion of the cardiovascular system which carries deoxygenated blood away from the heart, to the lungs, and returns oxygenated (oxygen-rich) blood back to the heart. The term pulmonary circulation is readily paired and contrasted with the systemic circulation. A separate system known as the bronchial circulation supplies blood to the tissue of the larger airways of the lung.
Pulmonary circulation is the movement of blood from the heart, to the lungs, and back to the heart again. De-oxygenated blood leaves the heart, goes to the lungs, and then re-enters the heart; deoxygenated blood leaves through the right ventricle through the pulmonary artery, the only artery in the body leaves the systemic circulation when it enters the right heart, more specifically the right atrium through the superior (upper) vena cava and inferior (lower) vena cava. The blood is then pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle. Blood is then pumped through the semilunar valve and into the pulmonary artery.
The pulmonary arteries carry deoxygenated blood to the lungs, where it releases carbon dioxide and picks up oxygen during respiration. Arteries are further divided in to very fine branches called the capillaries. In structure the capillaries are very thin walled. Their function is to assist in the carrying of blood to all cells of the body. The pulmonary vein returns oxygenated blood to the left atrium of the heart.
The oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. This blood then enters the left atrium, which pumps it through the bicuspid valve, also called the mitral or left atrioventricular valve, into the left ventricle. The blood is then distributed to the body through the systemic circulation before returning again to the pulmonary circulation.
Pulmonary circulation was first described by Ibn al-Nafis in his Commentary on Anatomy in Avicenna's Canon (1242). It was later described by Michael Servetus in the "Manuscript of Paris" (near 1546, never published) and later published in his Christianismi Restitutio (1553). Since it was a theology work condemned by most of the Christian factions of his time, the discovery remained mostly unknown until the dissections of William Harvey in 1616.
The pulmonary circulation loop is virtually bypassed in fetal circulation. The fetal lungs are collapsed, and blood passes from the right atrium directly into the left atrium through the foramen ovale, an open conduit between the paired atria. When the lungs expand at birth, the pulmonary pressure drops and blood is drawn from the right atrium into the right ventricle and through the pulmonary circuit. Over the course of several months, the foramen ovale closes, leaving a shallow depression known as the fossa ovalis in the adult heart.
- Michael Servetus Research Study on the Manuscript of Paris with the description of the Pulmonary Circulation, and more works by Servetus.
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- Young, R. A. (1940). "The Pulmonary Circulation--Before and After Harvey: Part I". BMJ 1 (4122): 1. doi:10.1136/bmj.1.4122.1. PMC 2176288. PMID 20782884.
- 2011 “The love for truth. Life and work of Michael Servetus”, (El amor a la verdad. Vida y obra de Miguel Servet.), printed by Navarro y Navarro, Zaragoza, collaboration with the Government of Navarra, Department of Institutional Relations and Education of the Government of Navarra, 607 pp, 64 of them illustrations, p 215-228 & 62nd illustration (XLVII)