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the heart.docx

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Biological Sciences
Kenneth Welch

The Heart Organization of the Cardiovascular System The cardiovascular system is divided into two circuits •Pulmonary circuit •blood to and from the lungs •System circuit •blood to and from the rest of the body •Vessels carry the blood through the circuits •Arteries carry blood away from the heart •Veins carry blood to the heart •Capillaries permit exchange Anatomy of the Heart The pericardia •Visceral pericardium or epicardium •Parietal pericardium •Pericardial fluid Superficial Anatomy of the Heart •The heart consists of four chambers •Two atria and two ventricles •Major blood vessels of the heart include •Inferior and superior vena cavae •Aorta and pulmonary trunk The Heart Wall •Components of the heart wall include •Epicardium •Myocardium •Endocardium Internal Anatomy and Organization •Atria •Thin walled chambers that receive blood from the vena cavae •Ventricles •Thick walled chambers separated from the atria by AV valves •Chordae tendineae •Tendinous fibers attached to the AV valves •Papillary muscle and trabeculae carneae •Muscular projections on the inner wall of ventricles Blood flow through the heart •Right atria •Tricuspid valve •Right ventricle •Pulmonary valve •Pulmonary circuit •Left atria •Bicuspid valve •Left ventricle •Aortic valve •Aorta and systemic circuit Heart chambers and valves •Structural Differences in heart chambers •The left side of the heart is more muscular than the right side •Functions of valves •AV valves prevent backflow of blood from the ventricles to the atria •Semilunar valves prevent backflow into the ventricles from the pulmonary trunk and aorta Connective Tissues •Connective tissue fibers of the heart •Provide physical support and elasticity •Distribute the force of contraction •Prevent overexpansion •The fibrous skeleton •Stabilizes the heart valves •Physically isolates atrial from ventricular cells Blood Supply to the Heart •Arteries include the right and left coronary arteries, marginal arteries, anterior and posterior interventricular arteries, and the circumflex artery •Veins include the great cardiac vein, anterior and posterior cardiac veins, the middle cardiac vein, and the small cardiac vein The Heartbeat Cardiac Physiology •Two classes of cardiac muscle cells •Specialized muscle cells of the conducting system •Contractile cells The Conducting System •The conducting system includes: •Sinoatrial (SA) node •Atrioventricular (AV) node •Conducting cells •Atrial conducting cells are found in internodal pathways •Ventricular conducting cells consist of the AV bundle, bundle branches, and Purkinje fibers Impulse Conduction through the heart •SA node begins the action potential •Stimulus spreads to the AV node •Impulse is delayed at AV node •Impulse then travels through ventricular conducting cells •Then distributed by Purkinje fibers The electrocardiogram (ECG) •A recording of the electrical events occurring during the cardiac cycle •The P wave accompanies the depolarization of the ventricles •The QRS complex appears as the ventricles depolarize •The T wave indicates ventricular repolarization Contractile Cells •Resting membrane potential of approximately –90mV •Action potential •Rapid depolarization •A plateau phase unique to cardiac muscle •Repolarization •Refractory period follows the action potential Calcium Ion and Ca
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