PET Exam 3 REVIEW Everything in red is what she brought up in class and in black is what I added from the notes and book What happens in the heart if the SA node pacemaker is nonfunctional o The AV node comes in and helps o If both are injured then the heart cant pump or contract o Because it has the fastest rate of depolarization the normal pacemaker of the heart is the SA node Make sure you understand the action potential going on in the heart o The AP initiated by the SA node travels through the conduction system to excite the working contractile muscle fibers in the atria and ventricles o Contractile fibers have a stable RMP of 90mV unlike autorhythmic fibers The AP propagates through the heart by opening and closing NA and K channels o Unlike skeletal muscle the refractor period in cardiac muscle lasts longer than the contraction itself another contraction cannot begin until relaxation is well underway o For this reason maintained contraction cant occur in cardiac muscle leaving sufficient time between contractions for the chambers to fill with blood o Mechanism of contraction Electrical activity leads to CA release from the SR actin and myosin filaments go through the contraction cycle and tension is developed as the filaments slide past one another Epinephrine released by the sympathetic nervous system increases contraction force by enhancing the movement of CA2 into the cytosol o Read the ekg QRS and T wave P wave atrial depolarization QRS wave ventricular depolarization and atrial repolarization T wave time it takes to empty the ventricles before they repolarize o Know what time part of the heart that depolarization and repolarization happens Depolarization of autorhythmic fibers in the SA node firing about once every 0 8 seconds or 75 action potentials per minute The action potential generated from the SA node reaches the next pacemaker by propagating throughout the wall of the atria to the AV node in the interatrial septum At the AV node the signal is slowed allowing the atrium a chance to mechanically move blood into the ventricles From the AV node the signal passes through the AV bundle to the left and right bundle branches in the interventricular septum towards the apex of the heart Finally the Purkinje fibers rapidly conduct the action potential throughout the ventricles 0 2 seconds after atrial contraction o Know when sodium is rushing into the stage Know about calcium Depolarization is the result of changes in membrane permeability to Na K and Ca depolarization Voltage gated Na channels open bringing about the depolarization phase of the action potential As these channels open Na diffuses into the cell causing rapid Depolarization also causes voltage gated Ca2 channels to open but these channels open and close much slower than Na channels Early repolarization occurs when the voltage gated Na channels and come voltage gates Ca channels close and a few K channels open Sodium ion movement into the cell slows o Repolarization Understand the long refractory period in the heart o Why we have it o The long refractory period ensures that contraction and most of relaxation are complete before another action potential can be initiated This prevents tetanic contractions in cardiac muscles and is responsible for rhythmic contractions Understand the cardiac cycle o It includes all events associated with one heartbeat including diastole relaxation phase and systole contraction phase of both the atria and the ventricles o Ventricular filling during ventricular diastole o Ventricular ejection during ventricular systole Heart rate x stroke volume cardiac output Understand flow of blood and when atrium is contracting o Electrical contraction in SA node o When blood leaves on left right side where does it go and enter o The action potential generated from the SA node reaches the next pacemaker by propagating throughout the wall of the atria to the AV node in the interatrial septum o At the AV node the signal is slowed allowing the atrium a chance to mechanically move blood into the ventricles o From the AV node the signal passes through the AV bundle to the left and right bundle branched in the interventricular septum towards the apex of the heart o The Purkinje fibers rapidly conduct the AP through the ventricles Where is the first and second heart rate is related to and why we hear it o Valves closing o Top part of the heart is a weak pump consisting of the right and left atria It loads the lower ventricles by giving an atrial kick before the ventricle contract o The bottom part of the heart is a strong pump consisting of the right and left ventricles It s the main pump for the pulmonary and systemic circuits o That s why the heart goes glug GLUG glug GLUG because the first pump is weaker Stroke Volume Volume of blood pump through each cardio cycle Understand preload and afterload o Preload the amt of ventricular filling before contraction o Afterload the resistance in the blood vessels of valves the heart is pumping into What happens in the heart Starling s Law o Increase in preload more forceful contraction or blood out of the heart o Relationship between preload and stoke volume o The more the heart muscle is stretched filled before contraction preload the more forcefully the heart will contract Stimulation of the sympathetic nervous system during exercises increases venous return stretches the heart muscles and increases the cardiac output What will happen if the heart receives more less parasympathetic vs sympathetic o Sympathetic activity increases the heart rate and the strength of myocardial contraction to increase blood flow out of the heart ejection fraction o When stimulated parasympathetic fibers in CN X the vagus nerve release acetylcholine that decreases heart rate and strength of contraction Parasympathetic activity slows the heart from its native rate of 100 bpm to about 70 80 in the average adult o The percentage of the total volume of red blood cells in the total volume of Hematocrit blood o The normal RBC mass is between 40 45 by volume this is the hematocrit Hct and corresponds to 4 6x106 mm3 by number Function of pericardial fluid o Lubricates the space between the visceral and parietal pericardium Angina disease state of heart o Angina pectoris is chest pain that results from a reduces blood supply to cardiac muscle o Often mistaken for indigestion o Most often results from narrowed and hardened coronary arterial walls Reduced blood flow and reduced supply
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