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Western University
Physiology 3120
Tom Stavraky

- 70% venous system, 15% heart and lungs, 10% arterial system, 5% Capillary Exchange - Blood to individual muscles can increase as much as 20-fold. Mitral Valve – Left heart, between the atrium and ventricle. Aortic Valve – Left heart Tricuspid Valve – Right heart Pulmonary Valve – Right heart - Mitral and tricuspid are referred to as the antriventricular valves while the aortic and pulmany valves are often referred to as the semilunar valves. Two types of cells in the heart: (1) Atrial and ventricular muscle fibers a. Rhythmicity (Self-excitability) (2) Specialized excitatory and conductive cells. a. Rapid conduction b. T-tubules are larger and run along Z-dics and are fewer c. Large amounts of mitochondria d. Capable of extracting 80% of oxygen from blood e. In syncytium i. Atrial syncytium and ventricular syncitium. Seperated by fibrous tissue called the atrioventricular ring. - 72 beats/min in vivo. Originated at SA node. Great sodium and calcium permeability. Potassium declines during diastole while the permeability for other ions does not change. Do not have a stable RMP. - Prepotential: Na+ goes through funny channels and Ca++ through T-type channels. - Depolarization: slow L-type channels - Repolarization: Calcium channels closing and potassium opening. - Rate can be altered by changing the slope of the prepotential or the ‘resting’ mp. - SA node activity spreads through internodal pathway and through interatrial myocardial band to left atrium. Then goes to AV node, bundle of His and to purkinje fibers. - Velocity is fastest in Purkinje Fibers, slowest in SA node and AV node. - AV would beat 40-60 bpm, purkinje would discharge at 15-40 bpm while the normal rate of SA node is 90 bpm. - Muscle fibers. Depolarization – opens fast Na+ channels - Rapid Repolarization – fast Na+ channels close, but Cl- opens and K+ starts leaking out - Plateau phase – K+ keeps leaking out, Ca++ enters - Restoration: Ca++ close and K+ continues - Resting potential: -90 mV - Calcium enters sarcoplasm by: (1) DHPR/Ca++ channels (2) Na/Ca++ exchanger (3) ryanodine/Ca channel on SR (4) Ca-induced-Ca release from SR. Levels increase 1000x. Most comes from SR but extracellular is still essential. - Relaxation: (1) Ca-ATPase pumps on SR membrane (80%) (2) Ca pump on SL (3) Na-Ca exchanger (15%) o Lasts 250-200 milliseconds. Absolutely refractory during most of the action potential. So no tetanus type contraction. - Electrocardiogram is the sum of all the electrical events in the heart P-wave – Depolarization of Atria QRS – depolarization of ventricles T-wave – repolarization of ventricles U-wave – repolarization of papillary muscles - As heart rate increases the PR interval decreases Cardiac Cycle Atrial systole – P wave. Atrial pressure is greater than ventricular pressure so AV valves are open and the ventricles fill (last 30%). This is the EDV Isovolumetric contraction – QRS complex represents the depolarization of the ventricles and they start conctracting. Ventricular pressure exceeds atrial pressure so AV valves close. Ejection Period – ventricles cont
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