Cardiac PhysiologyMycocardium: Thick muscle layerEndocardium: Inner layer that is continuous with endothelium of blood vesselsEpicardium: outer layer, is the visceral pericardium (like the peel on apple)Parietal Pericardium: lines the fibrous pericardiumFibrous pericardium: sac around the heartThe pericardial cavity has fluid which acts as lubricant for a beating heartPulmonary Circulation: Right side pumps blood to lungsSystemic Circulation: Left side pumps blood to rest of bodyBlood flow in heartBlood enters right atrium from vena cavaFlows past tricuspid valve into right ventricleContraction moves blood through pulmonary semilunar valve and into pulmonary arteries and into the lungsBlood returns to heart via pulmonary veins and into left atriumThrough bicuspid valve and into left ventricleThrough aortic semilunar valve and to rest of body (minus lungs)The heart is too thick to get nutrients via diffusion so it must get nutrients from coronary arteriesIf this is blocked, there is not enough oxygen to the heart and you will have heart attack (death of heart muscle)Valves in the heart allow one-way flow of blood and prevent backflowGap Junctions in heart allow positive charge to flow from cell to cellFunctional syncytiums are merging cells that act together (single unit smooth muscle).In the heart there are two functional syncytium, the atrium and ventriclesThe two syncytia are separated by fibrous Skelton that does not conduct impulses, only link between the two is at AV node.3The heart muscle like skeletal muscle, must have an action potential to contract but in the heart, this potential originates from the heart itself and not from neural stimulation (skeletal). This is due to pacemaker potential.Heart will beat on its own, outside the body since it has autorhythmicityInherent rate is 100BPM but resting rate is around 70 BPM since parasympathetic nervous system slows it down and acts as a brakeParasympathetic impulses decrease the slope of the pacemaker potential and increase time for cells to reach threshold.Sympathetic impulses increase the slope of the pacemaker potential an reduce time for cells to reach threshold.SA node is the pacemaker of a normal heart since its inherent rate is fastest (gets to threshold first)If the SA node is damaged, other areas take over but pacemaker is slowerIf AV and SA node are damaged, the purkinje fibers take over at 30 BPM4Refractory period of cardiac muscles is longThis prevents tetanic contraction of the heart and guarantees that there is time for heart to fillCardiac muscle action potential has a plateau that last as long as contractionAbsolute refractory period last about as long as tetanic contraction and tetanic contraction is prevented5Cardiac Action PotentialDepolarization caused by opening of voltage gated ion channelsChannels then close but membrane does not repolarizeK+ Permeability does not increase, It decreasesCa+ permeability increases (depolarization causes them to open)This brings in positive charge and keeps membrane depolarizedRepolarization occurs when Ca and K+ permeability return to normal and then K+ permeability increasesCa induced Ca release is when Ca+ enters cell which causes more Ca release from SRIncreased Ca+ in cytosol. Increased strength of contractionDecreased Ca+ in cytosol, decreased strength of contractionEpinephrine and Digitalis increase strength of contraction by increasing the amount of Ca+ in the cell cytosolIf you used a Ca+ channel blocker, you would decrease the force of contraction. If you blocked all channels, you would stop contraction 6SA node is located near the opening of the vena cava, which generates action potentials via pacemaker potentials. 100 BPM. Contracts atria togetherAV Node links atria signals to ventricles, it is in the right atrium. The impulse is delayed 0.1 seconds here to give time for the ventricles to fillAV bundle (bundle of His) is where the conductive tissues branch offPurkinje Fibers carry the impulse to the thick myocardium and signal most cells (others via cell to cell conduction) and causes contraction of the ventricles7EKG is a tool for evaluating electrical events in the heartNormal EKGDepolarization of the Atria – P waveDepolarization of Ventricles – QRS complexRepolarization of ventricles – T WaveRepolarization of Atria – Occurs during QRSDistance between P and R is PR segment and it indicates the nodal delay by AV nodeUseful in diagnosing heart blockPartial Heart Block occurs when some impulses get through AV node (every other P wave not followed by QRS complex)Complete Heart Block occurs when there is no correlation between P wave and QRS complex. P wave is on top of T waves and the ventricle is beating on its ownNo impulses are getting through the AV nodeComplete heart block would have 30-40 BPM (purkinje fibers) and would need to betreated with a pacemaker on ventricles since impulse from atria is blocked8Cardiac Arrhythmias are variations from normal heart rhythm Tachycardia – greater than 100 BPM (occurs during exercise and can occur in disease (high levels of thyroid hormone)Bradycardia (less than 60 BPM) can occur in athletes at rest. Also occurs in completeheart blockFlutter – very rapid over 200 BPM. Filling time is compromised and ventricles cannot fill. If this occurs for more than 30 seconds, need medical interventionFibrillation is cardiac chaos and happens when myocardium fail to contract together. 10% of people over 70 have atrial fibrillation (lose atrial kick) and don’t have complete fillingVentricular fibrillation needs to be corrected by defibrillation of the heartDepolarize all cells at once, get normal rhythm again9Cardiac Cycle is once complete heart beat (systole and diastole)Systole is contractionDiastole is relaxationCardiac Cycle occurs 70X/minStarts at SA node where pacemaker potential gets to threshold and impulse spreads through atrial myocardium and depolarization causes the P waveWith depolarization, atrium contract and top off the ventriclesVentricles then contract and ventricular pressure increases. This causes AV valves to close and makes the first heart sound (lub of “lub dup”)Pressure continues to rise in an isovolumetric contraction until ventricular pressureis greater than aortic pressure whereupon the semilunar valves open and blood is ejected from the heartVentricle then repolarizes in the T wave. During repolarization is relaxation, semilunar valve closes since aortic pressure > ventricular and the