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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