Study Guide Chapter 18

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The Cardiovascular System: The Heart- Chapter 18
Heart Anatomy
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. Lines the heart chambers and covers the fibrous skeleton of the valves

Chambers and Associated Great Vessels
* Four chambers
* Two atria
* Longitudinally Separated internally by the interatrial septum * Coronary sulcus (atrioventricular groove) encircles the junction of the atria and ventricles * Auricles increase atrial volume

* Two ventricles
* Longitudinally Separated by the interventricular septum * Right ventricle forms most of the anterior surface of the heart * Left ventricle dominates the inferoposterior aspect of the heart and forms the heart apex * Coronary sulcus or atrioventricular groove- encircles the junction of the atria and ventricles like a crown (corona=crown) * Anterior and posterior interventricular sulci mark the position of the septum externally

Atria: The Receiving Chambers
* Except for small, wrinkled, protruding appendages called auricles, which increase the atrial volume somewhat, the right and left atria are remarkably free of distinguishing surface features. * Internally the right atrium has two basic parts: a smaooth-walled posterior part and an anterior portion in which the walls are ridged by pectinate muscles (pectin=comb) * The posterior and anterioir regions of the right atrium are separated by a C-shaped ridge called the crista terminalis (“terminal crest”) * In contrast, the left atrium is mostly smooth and pectinate muscles are found only in the auricle. * The interatrial septum bears a shallow depression, the fossa ovalis, which marks the spot where an opening, the foramen ovale, existed in the fetal heart. * Functionally, the atria are receiving chambers for blood returning to the heart from the circulation (atrium= entryway) * Relatively small, thin-walled chambers because they need contract only minimally to push blood “downstairs” into the ventricles * Vessels entering right atrium

* Superior vena cava-...
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