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Lecture 3

WEEK 3- The Heart.pdf

19 Pages

Course Code
BIOL 271

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The Heart pumps over 5 million litres of blood a year through over 120,000 km of blood vessels Orientation in mediastinum region medial to lungs, superior to diaphragm, inferior to thoracic inlet, posterior to sternum contains heart and great vessels, trachea, thymus gland, esophagus "tipped inverted cone" base: (top) directed to the posterior, superior, right (right shoulder) apex: (bottom) directed to the anterior, inferior, left (left foot) pointed to anterior, right surface projection apex lies in 5th intercostal space, about 9 cm (1 hand- width) to L of midline Coverings pericardium surrounds and protects the heart allows space for movement of heart outer fibrous sac, inner serous layer that lines sac and covers heart fibrous pericardium dense irregular CT (bag around heart) protects the heart prevents over stretching serous pericardium thin delicate membrane two layers parietal layer: lines fibrous pericardium cavity visceral layer covers the heart pericardial cavity between parietal and visceral pericardium contains serous fluid epicardium visceral layer of serous pericardium myocardium cardiac muscle thickest layer of the heart wall endocardium forms valves, lines chambers very smooth, so blood doesn't clot Chambers and Sulci four chambers 2 atria 2 ventricles sulci grooves on surface of heart contain coronary blood vessels and fat not visible, because filled with b.v. and fat keeps b.v.s protected from damage, by surrounding them coronary sulcus encircles heart lies between atria and ventricles anterior interventricular sulcus boundary between ventricles on anterior surface of heart posterior interventricular sulcus boundary between ventricles on posterior surface of heart Right Atrium receives blood from: superior vena cava inferior vena cava coronary sinus drains deoxygenated blood from circulatory system right atrium is like the lobby: only entrance to the heart fossa ovalis depression in intertribal septum remnant of the foramen ovale (from fetal period) connected right and left atria closes w/in minutes of being born Tricuspid valve three cusps (flap of tissue / door) dense CT covered with endocardium blood passes through to enter R ventricle prevents back flow from R ventricle to R atrium Right Ventricle forms most of anterior surface of heart papillary muscles cone shaped trabeculae carneae (raised bundles of cardiac muscle) chordae tendineae cord-like structures that connect valve cusps to papillary muscles prevent eversion (inverting of valve under pressure) interventricular septum wall between R and L ventricles pulmonary semilunar valve blood passes through to enter pulmonary trunk prevents from pulmonary trunk to R ventricle Left Atrium receives blood from lungs via 4 pulmonary veins (2 from each lung) Bicuspid (mitral) Valve blood passes through to enter L ventricle prevents from L ventricle to L atrium anchored by chord tendineae and papillary muscles Left Ventricle forms the apex of the heart aortic semilunar valve blood passes through to enter aorta prevents backflow from aorta to L ventricle Myocardial Thickness and Function artria have thin walls deliver blood to ventricles ventricle walls are much thicker and stronger R ventricle pumps blood through pulmonary circulation (lungs) L ventricle pumps blood through systemic circulation (body); has thickest wall myocardium of L ventricle is much thicker than that of R Fibroskeleton of Heart dense CT rings surrounding heart valves electrical insulator between atria and ventricles heart valves absolutely essential that blood only flows in 1 direction valves prevent back flow of blood; regulate 1-way flow through heart Atrioventricular valves (2) between atria and ventricles prevent backflow of blood from ventricles to atria supported by chordae tendineae and papillary muscles (— do not cause opening and closing of valves; rather it is the blood pressure on the ventricle that forces it open) AV valves open... when ventricles relax (intraventricular pressure is lower than intraatrial pressure) chord tendineae are slack, papillary muscles are relaxed blood enters ventricles AV valves close… when ventricles contract, intraventricular pressure rises, blood pushes valves closed chordae tendineae are taut, papillary muscles contract (prevent eversion) prevents backflow of blood to atria Semilunar Valves (2) between ventricles and arteries pulmonary SLV prevents backflow of blood from pulmonary trunk to R ventricle aortic SLV prevents backflow of blood from aorta to L ventricle open when ventricles contract blood flows from ventricles into pulmonary trunk and aorta close when ventricles relax blood flowing back from arteries fills valve cusps, closes valves tightly prevents blood from returning to ventricles Blood Flow >RA>>RV>>Lungs>>LA>>LV>>Body> Circulation of Blood 2 closed circuits Systemic L side of heart pumps oxygenated blood to body L ventricle to aorta aorta branches into many arteries that supply organs arteries branch into many arterioles in tissues arterioles branch into thin-walled capillaries for exchange of gases and nutrients deoxygenated blood is drained via venules venules merge into veins and return blood to R atrium via vena cava Pulmonary R side of heart pumps deoxygenated blood to lungs R ventricle to pulmonary trunk pulmonary trunk branches into pulmonary arteries oxygenated blood returns to L atrium via pulmonary veins Coronary Circulation heart needs its own blood circulation—cannot use blood it is pumping when blood enters the ascending aorta, blood pressure distends the aortic wall when the ventricles relax, some blood in the ascending aorta is forced into coronary vessels by the elastic recoil of the aortic wall branch off aorta superior to aortic semilunar valve cusps fill with blood and close valves; blood travels down alternate paths (R+L coronary arteries) many anastomoses connections between arteries (like the backroads) supply blood to the same region provide alternate routes if one artery becomes occluded [blocked] left coronary artery anterior interventricular branch supplies both ventricles circumflex branch (around to posterior surface of heart) in coronary sulcus supplies L atrium and ventricle right coronary artery in coronary sulcus marginal branch supplies R ventricle posterior interventricular branch supplies both ventricles between R + L coronary arteries, an anastamosis with the circumflex branch and R coronary artery Cardiac Veins drain blood from the myocardium drain into coronary sinus coronary sinus drains into R atrium Cardiac Muscle (cardiomyocyte) Histology consists of partially striated branched cells, connected by intercalated dis
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