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SC BIOL 244 - Heart Part 1

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BIOL 244 Chapter 18: Heart Lecture 9 (September 18) Pulmonary Circuit: shunts the carbon dioxide rich blood entering its chambers to the lungs to unload carbon dioxide & pick up oxygen, then back to the left side of the heart Location: right side of the heart Function: provides for gas exchange in the lungs Systematic Circuit: carries oxygen; receives oxygenated blood returning from the lungs & pups this blood throughout the body to supply oxygen & nutrients to body tissues Location: left side of the heart Function: provides functional blood supply to all body tissues Coronary Circuit: functional blood supply of the heart; shortest circulation in the body Location: right & left coronary arteries issue from base of aorta, encircle heart in coronary sulcus Function: functional blood supply to the heart Coronary Arteries Provide intermittent, pulsating blood flow to myocardium Deliver blood when heart is relaxed but are ineffective when ventricles are contracting because they are compressed by contracting myocardium Left Coronary Artery- Anterior Interventricular artery: follows anterior interventricular sulcus & supplies blood to interventricular septum and anterior walls of both ventricles- Circumflex artery: supplies atrium & posterior walls of left atrium Right Coronary Artery: supplies right atrium & nearly all right ventricle- Right Marginal Artery: serves myocardium of lateral right side of heart- Posterior interventricular artery: runs to heart apex and supplies posterior ventricular walls (merges with anterior interventricular artery) Coronary Veins Cardiac veins follow path of coronary arteries & join to form coronary sinus (empties blood into right atrium)- Great cardiac vein in anterior interventricular sulcus- Middle cardiac vein in posterior interventricular sulcus- Small cardiac vein runs along hearts right inferior margin Pericardium: double-layered sac enclosing heart & forming superficial layer; has fibrous & serous layer Fibrous pericardium: loosely fitting superficial part Tough, dense, connective tissue Protects the heart Anchors it to surrounding structures Prevents overfilling of the heart with blood Serous pericardium: thin, slippery, 2-layer serous membrane that forms a closed sac around the heart Parietal layer lines internal surface of fibrous pericardium Heart wall: richly supplied with blood vessels Epicardium “upon the heart” Visceral layer of serous pericardium Often infiltrated with fat (especially in older people) Myocardium “muscle heart” Middle layer that contracts Composed of mainly cardiac muscle & forms bulk of heart Branching cardiac muscle cells are tethered together by crisscrossing connective tissue fibers and arranged in spiral bundles that link all parts of the heart together Cardiac skeleton: reinforces myocardium internally & anchors the cardiac muscle fibers- Limits spread of action potentials to specific pathways in the heart- Drained by great, middle, & small cardiac veins Endocardium “inside the heart” Glistening white sheet of endothelium (squamous epithelium) resting on thin connective tissue layer Located on inner myocardial surface Lines heart chambers & covers fibrous skeleton of valves Cardiac muscle Bulk of heart is contractile muscle fibers responsible for heart’s pumping activity Microscopic anatomy Striated & contracts using sliding filaments Short, fat, branched, & interconnected Each fiber contains 1-2 large pale, central located nuclei Plasma membrane of adjacent cardiac cells interlock using intercalated discs- Desmosomes: prevent adjacent cells from separating during contraction- Gap junctions: allow ions to pass from cell to cell- Myocardium behaves as single coordinated movement (functional syncytium) Cardiac sarcoplasmic reticulum is simpler & lacks large terminal cisterns of skeletal muscle (don’t have triads) Mechanism & events of contraction Means of Stimulation- Some are self-excitable- Automaticity/authorhythmicity: ability of cell to initiate not only their own depolarization, but that of the whole heart Organ vs. Motor Unit Contraction- Contraction is all-or-none because gap junctions electrically tie all cardiac muscle cells together into a single contractile unit- Depolarization wave travels across heart from cell to cell via ion passage through gap junctions Length of Absolute Refractory Period > 200 ms to prevent tetanic contractions (would stop heart’s pumping action) Heart Chambers Atria: receiving chambers Auricles: small, wrinkled protruding appendages that increase the atrial volume Relatively small, thin-walled chambers b/c they only need minimal contractions to push blood “downstairs” into ventricles Right atrium: deoxygenated blood- Pectinate muscles- Crista terminalis- C shaped ridge that separates anterior & posterior regions of right atrium- Feeds blood into lungs- Blood enters right atrium via Superior vena cava- returns blood from body areas superior to diaphragm Inferior vena cava- returns blood from body areas inferior to diaphragm Coronary sinus- collects blood draining from myocardium Left atrium: oxygenated blood- Mostly smooth, pectinate muscles only found in auricles- Interatrial septum fas fossa ovalis- marks spot where foramen ovale was in fetal heart- 4 pulmonary veins enter left atrium Transport blood from lungs back to heart Trabeculae carneae: mark the internal walls of ventricular chamber Ventricles: discharging chambers; contract & propel blood out of heart into circulation Right ventricle: pumps blood into pulmonary trunk which routes blood to lungs where gas exchange occurs Left ventricle: ejects blood into aorta (largest artery in body) which routes blood to entire rest of body Valves in the heart Atrioventricular valves: prevent backflow into atria when ventricles are contracting; located between atriums and ventricles Right AV valve (Tricuspid): 3 cusps=flaps of endocardium reinforced by connective tissue cores Left AV vale (mitral/bicuspid): 2 cusps When ventricles contract, blood compressed in chambers & intraventricular pressurerises, forcing blood superiorly against valve flaps and valve closes Semilunar Valves: guard the bases of large arteries issuing from the ventricles (aorta & pulmonary


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SC BIOL 244 - Heart Part 1

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