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解剖学= = = =[[文件:心脏location.jpg | |“弗拉姆”eless]] The heart is a conical hollow muscular organ situated in the middle mediastinum and is enclosed within the pericardium. It is positioned posteriorly to the body of the sternum with one-third situated on the right and two-thirds on the left of the midline. The heart measures 12 x 8.5 x 6 cm and weighs ~310 g (males) and ~255 g (females). It pumps blood to various parts of the body to meet their nutritive requirements. The Greek name for the heart is cardia from which we have the adjective cardia. <ref>Chaurasia BD. [https://www.pdfdrive.com/bd-chaurasia-books.html Human Anatomy Regional and Applied Dissection and Clinical. Vol 1]. CBS Publishers and Distributors Pvt Ltd, 2010 </ref> Relations * Anteriorly: the body of the sternum, and adjoining costal cartilages; left lung, and pleura (apex) * Posteriorly: oesophagus, descending thoracic aorta, azygos, hemiazygos veins, and thoracic duct * Superficially : bifurcation of the main pulmonary trunk * Inferiorly: diaphragm * Laterally: lungs, pleura<ref name=":6">Radiopedia Heart Available: https://radiopaedia.org/articles/heart?lang=gb (accessed 17.6.2021)</ref> === Layers of the Heart Walls === [[File:Heart layers.jpg|right|frameless|399x399px]] The heart wall consists of three layers enclosed in the pericardium<ref name=":2" /><ref name=":3">Malouf, JF, Edwards, WD, Tajil, AJ, Seward, JB. Functional anatomy of the heart. In: Fuster, F, Alexander, RW, O’Rourke, RA editors. Hurst’s: The Heart. 10th edn. McGraw-Hill Inc., 2001. p19–62. </ref><ref name=":5">Drake, RL, Vogl, W, Mitchell, AW, Gray, H. Gray's anatomy for Students 2nd ed. Philadelphia : Churchill Livingstone/Elsevier, 2010. </ref>: # Epicardium - the outer layer of the wall of the heart and is formed by the visceral layer of the serous pericardium. # Myocardium - the muscular middle layer of the wall of the heart and has excitable tissue and the conducting system. # Endocardium .<ref name=":6" /> * A middle concentric layer * A subendocardial layer. The rest of the heart is composed mainly of the subepicardial and subendocardial layers. === Structure and Function === [[File:Human-heart-chambers.jpg|right|frameless|399x399px]] The heart is subdivided by septa into right and left halves, and a constriction subdivides each half of the organ into two cavities, the upper cavity being called the atrium, the lower the ventricle. The heart, therefore, consists of four chambers: * right atrium * left atrium * right ventricle * left ventricle<ref name=":6" />. It is best to remember the four chambers and four valves in order of the series that blood travels through the heart: * Venous blood returning from the body drains into the right atrium via the [[Vena Cava|SVC, IVC]] and coronary sinus * The right atrium pumps blood through the tricuspid valve into the right ventricle * The right ventricle pumps blood through the pulmonary semilunar valve into the pulmonary trunk to be oxygenated in the lungs * Blood returning from the lungs drains into the left atrium via the four pulmonary veins * The left atrium pumps blood through the bicuspid (mitral) valve into the left ventricle * The left ventricle pumps blood through the aortic semilunar valve into the ascending [[aorta]] to supply the body.<ref name=":6" /> === Heart Valves === [[File:Heart Valves.jpg|right|frameless|399x399px]] The valves of the heart maintain unidirectional flow of the blood and prevent its regurgitation in the opposite direction. There are two pairs of valves in the heart, a pair of atrioventricular valves and a pair of semilunar valves. Apart, it has four valves. All four valves of the heart have a singular purpose: allowing forward flow of blood but preventing backward flow.<ref name=":0">Rehman I, Rehman A. Anatomy, Thorax, Heart. [Updated 2020 Dec 28]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan Available:https://www.ncbi.nlm.nih.gov/books/NBK470256/ (accessed 17.6.2021)</ref> The outflow of each chamber is guarded by a heart valve: Atrioventricular valves between the atria and ventricles # tricuspid valve (R side of the heart) # mitral valve/bicuspid valve (left side of the heart) Semilunar valves which are located in the outflow tracts of the ventricles # aortic valve (L side heart) # pulmonary valve (R side heart)<ref name=":6" /> See also [[Cardiac Valve Defects]]
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