Heart Circulatory system includes the heart blood vessels and blood responsible for transportation projection and regulation Cardiovascular system includes the heart and blood vessels responsible for only the transportation of blood Cardiovascular System Pulmonary circuit the right side of the heart supplies blood to lungs to be oxygenated Systemic circuit left side of the heart supplies blood to all organs of the body Heart located in thoracic cavity and is contained by the mediastinum the thick median partition of the thoracic cavity that separates one pleural cavity from the other 4 inches wide 5 inches long 6 inches thick weighs less than a pound Heart walls Epicardium largest branches of the coronary blood vessels travel through the epicardium Myocardium made up of cardiac muscle is the thickest layer because it does the work of the heart left is thicker than the right side cardiac muscle tissue is spiral or circular bundles that link all parts of the heart together fibrous skeleton framework of collagenous and elastic CT fibers functions structural support anchors cardiac muscle fibers non conductor of electricity limits the spread of action potentials Endocardium lines the interior of the heart chambers no adipose tissue covers the valve surfaces and is continuus with the endothelium of the blood vessels Pericardium made of two walls pericardial sac parietal pericardium serous layer deep and thin layer fibrous layer tough superficial layer made up of dense CT epicardium visceral pericardium formed by the serous layer turning inward at the base of the heart space between the parietal and visceral membranes is called pericardial cavity and contains pericardial fluid functions lubrication reduce friction protection expansion of heart and prevents excessive expansion Cardiac Muscle Tissue Has a single central nucleus Mitochondria is 25 of the volume of the cell The sarcomeres are similar to skeletal muscle Sarcoplasmic reticulum is less developed no terminal cisternae Has much larger T tubules than skeletal muscle admits calcium ions from ECF to activate muscle contraction Joined end to end by intercalated discs complex steplike structure with 3 distinctive features not found in skeletal muscle 1 Interdigitating folds looks like the bottom of an egg carton interlock and increase the surface area of intercellular contact 2 Mechanical junction fascia adherens broad band in which actin of the thin myofilaments is anchored to the plasma membrane and each cell is linked to the next via transmembrane proteins desmosomes patches of mechanical linkage between cells prevent contracting cardiocytes from pulling apart 3 Electrical junction gap junction that enables each cardiocyte to electrically stimulate its neighbors functional syncytium though the heart is composed of many different cells they all beat together and act as a single cell Cardiac Muscle Metabolism aerobic metabolism needs oxygen in order to make ATP not prone to fatiguing adaptable to organic fuels at rest it is 60 fatty acids 35 glucose 5 other fuels can change metabolic pathways to use different substances for fuel can even use lactic acid Cardiac Conduction System Autorhythmic cells are modified cardiac muscle cells 1 of total function independently but are influenced by ANS hormones function as pacemakers and a conduction pathway Depolarization Rate SA node pacemaker 70 80 times min AV node acts as an electrical gateway to the ventricles 40 50 times min AV bundle and Purkinje fibers AV bundle is the pathway by which signals leave the AV node Purkinje fibers distribute electrical excitation to the cardiocytes of the ventricles 20 40 times min Pacemaker Physiology of SA Has an unstable resting membrane potentional pacemaker potential membrane potential starts at 60mV and drifts upward gradual depolarization Pictured on Graph Reduced K permeability Slow Na inflow Fast Ca channels Depolarization Fast K outflow Impulse Conduction to the Myocardium Cadiac conduction system stimulus is required to initiate the action potential All or none either whole organ contracts or none of it does The artia and ventricles are not electrically connected they experience functional syncytium contract together no matter what Purkinje Fibers are the fastest conducting fibers in the system supply the papillary muscles to contract and take up slack in the tendinous cords Electrical Behavior of Myocardium Individual contractile cardiac myocyte aka cardiocyte resting membrane potential of 90mV normally depolarize only when stimulated unlike cells of the SA node Graph Rapid depolarization a stimulus opens voltage gated sodium channels causing a Na inflow Plateau phase action potentials open slow calcium channels which admits Ca to flow in Repolarization Ca channels close and K channels open membrane voltage drops and muscle tension declines soon after Absolute Refraction longer than skeletal muscle prevents wave summation and tetanus would stop pumping action of heart