Size, Location, and Orientation * Approximately the size of a fist * Location * In the mediastinum between second rib and fifth intercostal space * On the superior surface of diaphragm * Two-thirds to the left of the midsternal line; balance projects to the right * Anterior to the vertebral column, posterior to the sternum
Coverings of the Heart * Enclosed in pericardium, a double-walled sac * Superficial fibrous pericardium * Protects the heart * Anchors it to surrounding structures * prevents overfilling of the heart with blood * Deep two-layered serous pericardium * Parietal layer lines the internal surface of the fibrous pericardium * Visceral layer (epicardium) on external surface of the heart * Separated by fluid-filled pericardial cavity (decreases friction) * Contains a film of serous fluid * Allowing the mobile heart to work in a relatively friction-free environment
Layers of the Heart Wall 1. Epicardium—visceral layer of the serous pericardium 1. Often infiltrated with fat, especially older people. 2. Myocardium (“muscle heart”) 2. Spiral bundles of cardiac muscle cells that form the bulk of the heart 3. Layer that contracts 4. Fibrous skeleton of the heart: crisscrossing, interlacing layer of connective tissue 1. Anchors cardiac muscle fibers 2. Supports great vessels and valves 1. Without support they might eventually become stretched because of the continuous stress of blood pulsing through them 3. Limits spread of action potentials to specific paths 3. Endocardium (“inside the heart”) is continuous with endothelial lining of blood vessels leaving the entering the heart. 5. White sheet of endothelium (Squamous epithelium) resting on a think connective tissue layer 6.