Cardiovascular System 02 17 2011 The Cardiovascular System The function of the cardiovascular system is to deliver oxygen and nutrients and to remove carbon dioxide and other waste products Transport of substances such as o Oxygen and nutrients to cells o Wastes from cells to liver and kidneys o Hormones immune cells clotting proteins to specific target cells A closed system of the heart and blood vessels o The heart pumps blood o Blood vessels allow blood to circulate to all parts of the body Blood is used for delivery Overview of the Cardiovascular System The Heart o Located in the thoracic cavity o Diaphragm separates abdominal cavity from thoracic cavity o Size of fist o Weighs approximately 250 350 grams o Valves present for unidirectional blood flow o Four chambers 2 atria and 2 ventricles Blood Vessels Blood The Heart mediastinum Orientation Location is in the thorax between the lungs in the inferior o Pointed apex directed toward left tip o Base points toward right shoulder Properties of Cardiac Muscle Intercalated o Gap junctions so heart contracts as a unit o Desmosomes resist stress Aerobic muscle No cell division after infancy growth by hypertrophy 99 contractile cells 1 autorhythmic cells The Heart s Covering The Pericardium Pericardium is a double walled membranous sac surrounding heart o Fibrous pericardium is loose and superficial o Serous pericardium is deep to the fibrous pericardium and composed of two layers epicardium Visceral pericardium next to heart also known as the Parietal pericardium outside layer that lines the inner surface of the fibrous pericardium o Serous fluid fills the space between the layers of pericardium o Lubricates heart decreasing friction o Pericarditis inflammation of pericardium Walls of the Heart Three layers o Epicardium Outside layer Visceral pericardium Connective tissue layer o Myocardium Middle layer Mostly cardiac muscle o Endocardium Inner layer Endothelium Walls of ventricles thicker than walls of atria Wall of left ventricle thicker than wall of right ventricle The Heart 4 Chambers Right and left side act as separate pumps Septa separate chambers Interventricular septum o Separates the two ventricles Interatrial septum o Separates the two atria Four chambers o Atria are receiving chambers o Ventricles are discharging chambers Right atrium Left atrium Right ventricle Left ventricle The Heart Valves Allow blood to flow in only one direction to prevent backflow o Four valves ventricles Atrioventricular AV valves are between atria and Bicuspid mitral valve left side of heart Tricuspid valve right side of heart Semilunar valves are between ventricle and artery Pulmonary semilunar valve Aortic semilunar valve o Anchored in place by chordae tendineae heart strings o Open during heart relaxation and closed during ventricular AV valves contraction Semicircular valves contraction o Closed during heart relaxation but open during ventricular These valves operate opposite of one another to force a one way path of blood through the heart Valves and Unidirectional Blood Flow Pressure within chambers of heart vary with heartbeat cycle Pressure difference drives blood flow high pressure to low pressure Normal direction of flow o Veins to atria o Atria to ventricles o Ventricles to arteries Valves prevent backward flow of blood All open passively based on pressure gradient AV Valves Open Blood returning to the atria puts pressure against AV valves the AV valves are forced open As the ventricles fill AV valve flaps hang limply into ventricles Atria contract forcing additional blood into ventricles AV Valves Close Ventricles contract forcing blood against AV valve flaps AV valves close Chordae tendineae tighten preventing valve flaps from everting into atria Semilunar Valves As ventricles contract and intraventricular pressure rises blood is pushed up against semilunar valves forcing them open As ventricles relax and intraventricular pressure falls blood flows back from arteries filling the leaflets of semilunar valves and forcing them to close Blood Vessels Vasculature the heart away from the heart Heart Arteries Arterioles Capillaries Venules Veins back to Arteries are relatively large branching vessels that conduct blood Arterioles are small branching vessels with high resistance Capillaries are the site of exchange between blood and tissue Venules are small converging vessels Veins are relatively large converging vessels that conduct blood to the heart Closed system Pressure drives blood flow Series Flow Through the Cardiovascular System Parallel flow within the systemic or Pulmonary circuit o Pulmonary circuit o Systemic circuit Supplied by right heart Blood vessels from heart to lungs and lungs to heart Supplied by left heart Blood vessels from heart to systemic tissues and tissues to heart Cardiovascular system closed system Left ventricle aorta systemic circuit venae cavae right atrium right ventricle pulmonary artery pulmonary circuit pulmonary veins left atrium left ventricle Oxygenation of Blood Exchange between blood and tissue takes place in capillaries Pulmonary capillaries o Blood entering lungs deoxygenating blood o Oxygen diffuses from tissue to blood o Blood leaving lungs oxygenated blood Systemic capillaries o Blood entering tissues oxygenated blood o Oxygen diffuses from blood to tissue o Blood leaving tissues deoxygenated blood Blood Flow Through the Heart Coronary Circulation Intrinsic conduction system nodal system heart muscle cells contract without nerve impulses in a regular continuous way Blood in the heart chambers does not nourish the myocardium The heart has its own nourishing circulatory system consisting of o Coronary arteries branch from the aorta to supply the heart muscle with oxygenated blood o Cardiac veins drain the myocardium of blood o Coronary sinus a large vein on the posterior of the heart receives blood from cardiac veins Blood empties into the right atrium via the coronary sinus Bypass surgery Function of Cardiac Muscle Rhythmic contraction and relaxation generates heart pumping action Contraction pushes blood out of heart into vasculature Relaxation allows heart to fill with blood The Heart Conduction System Special tissue sets the pace o Sinoatrial node SA node pacemaker is in the right atrium o Atrioventricular node AV node is at the junction of the atria o Atrioventricular bundle AV bundle bundle of His is in the and ventricles interventricular septum o Bundle branches are in the
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