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The heart is a pear-shaped organ located in the thoracic cavity.
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| Submitted: Thu Sep 25 2003
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The Heart (unit 1) The heart is a pear-shaped organ located in the thoracic cavity. It lies underneath the sternum between the lungs. The heart consists of three layers. 1. The pericardium; which is an outer, double layered bag containing a thin film of fluid. Its function is to reduce friction between the heart and other parts of the thoracic cavity and to maintain the heart shape. 2. The myocardium, or cardiac muscle; contracts in the same way as skeletal muscle. The heart has a pacemaker which sends impulses throughout the myocardium. Because of its united structure, all cells forming the entire myocardium muscle sheet contract together, producing a heartbeat. This is the all or none law. 3. The Endocardium, which prevents friction between the heart muscle and flowing blood. The heart has four chambers; two atria and two ventricles. During Serena's match, there are many short-term responses taking place concerning the heart....
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