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Heart outline - Chapter 20 The Heart I The Organization of...

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Chapter 20: The Heart I. The Organization of the Cardiovascular System, p. 670 The heart pumps blood through 2 separate circuits of blood vessels: 1. The pulmonary circuit : carries blood to and from the gas exchange surfaces of the lungs 2. The systemic circuit : carries blood to and from the rest of the body Circulating blood alternates between the systemic and pulmonary systems: Blood returning to the heart from the systemic circulation must pass through the pulmonary circuit before returning to the systemic circuit. There are 3 types of blood vessels: 1. Arteries carry blood away from the heart 2. Veins carry blood to the heart 3. Capillaries are networks of small, thin-walled vessels between arteries and veins. Capillaries are called exchange vessels because they are the location where dissolved gases, nutrients, and wastes are exchanged between the blood and the surrounding tissues. The heart has 4 chambers, 2 for each circuit: 1. The right atrium collects blood from the systemic circuit. 2. The right ventricle pumps blood to the pulmonary circuit. 3. The left atrium collects blood from the pulmonary circuit. 4. The left ventricle pumps blood to the systemic circuit. II. Anatomy of the Heart, p. 670 The heart is located directly posterior to the sternum. The great veins and arteries attach at the top (the base ). The pointed tip is the apex . The heart, surrounded by the pericardial sac , sits in the mediastinum (between the 2 pleural cavities) which also holds the great vessels, thymus, esophagus and trachea. The Pericardium, p. 671 The pericardial cavity has a double lining called the pericardium . The outer layer is the parietal pericardium . The parietal pericardium forms the inner layer of the fibrous pericardial sac which surrounds and stabilizes the heart. The inner layer is the visceral pericardium . The space between the 2 layers is the pericardial cavity , which contains a small amount of lubricating pericardial fluid . An infection of the pericardium is called pericarditis . Superficial Anatomy of the Heart, p. 672 The atria are thin-walled, with an expandable outer portion called the auricle . A coronary sulcus divides the atria and the ventricles. The left and right ventricles are separated along the anterior and posterior interventricular sulci , which also contain the blood vessels that supply the cardiac muscle. The Heart Wall, p. 673
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The heart wall has 3 layers: 1. the outer epicardium 2. the middle myocardium 3. the inner endocardium - Cardiac Muscle Tissue Cardiac muscle cells are interconnected by intercalated discs which are held together by desmosomes and linked by gap junctions. Intercalated discs convey the force of contraction from cell to cell and propagate action potentials. The characteristics of cardiac muscle cells include: 1. small size 2. single, central nucleus 3. branching interconnections between cells 4. intercalated discs Table 20-1 summarizes differences between cardiac cells and skeletal fibers.
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