Heart Physiology Intrinsic Conduction Autorhythmic cells have unstable resting membrane potentials Autorhythmic Cell Location Sinoatrial node AV node Bundle of His Bundle branches Autorhythmic Cell Location Sinoatrial node AV node Bundle of His Bundle branches Purkinje fibers Extrinsic Innervation Cardioacceleratory center Cardioinhibitory center ECG Graphic recording of electrical events of the heart Deflection waves Anatomy Joke of the Day Heart Sounds AV valves closing SL valves closing Murmur heart sounds intro html http www med ucla edu wilkes Cardiac Cycle Systole phase of contraction and diastole phase of relaxation of both atria plus systole and diastole of both ventricles Cardiac Output Product of stroke volume amount of blood that leaves heart with each beat and heart rate of beats per min CO 75 bpm x 70 ml b CO 5250 ml min Cardiac reserve Stroke Volume Difference between amount of blood in ventricles before and after systole End diastolic volume end systolic volume 120 ml 50 ml 70 ml Factors Affecting Stroke Volume Stretch of cardiac muscle determined by amount of blood that returns to atria heart and gets passed through ventricles more fluid means more stretch Starling Law of the heart increased stretch of the heart due to increase in fluid vol equals greater contractions Contraction strength not due to stretch contractility which results from increased Ca influx more Ca equals more contraction increased Ca is from nervous stimulation Arterial pressure affects stroke vol afterload as BP increases there is reduction in amount of blood that leaves heart Cardiac Output Product of stroke volume and heart rate CO 75 bpm x 70 ml b CO 5250 ml min Cardiac reserve Factors Affecting Heart Rate Sympathetic nervous system activation Norepinephrine causes depolarization Corresponding increase in contractility Parasympathetic nervous system activation decreases heart activity Acetylcholine causes hyperpolarization Adrenal medulla production of epinephrine increases heart rate Thyroid production of thyroxine increases heart rate gradually and it stays there for long time Blood pressure changes baroreceptors Ionic balances ionic composition of plasma portion of blood can change heart rate Age Sex gender higher in women Exercise after affect Temperature higher BP with fever Anatomy Joke of the Day Vagal Tone Related Pathologies Tachycardia abnormally high resting rate my age greater than 100 beats per min Bradycardia abnormal pathological low resting rate my age less than 60 beats per min Congestive heart failure dangerously low cardiac output many reasons why this can happen Coronary atherosclerosis closing off of coronary arteries results in stints or bypass heart is not receiving O so it cant beat High blood pressure pressure in arteries keeps heart from expelling blood Myocardial infarctions heart attacks Dilated cardiomyopathy stretched flabby ventricles loss of muscle tone in ventricles Heart Development Derived from mesoderm Originates as two endothelial tubes Tubes fuse into single chambered heart by day 23 Early chambers formed by day 25 Heart Development Derived from mesoderm Originates as two endothelial tubes Tubes fuse into single chambered heart by day 23 Early chambers formed by day 25 D looping and structural changes divide heart into separate chambers and change orientation by day 46 Foramen Ovale Connection of two atria through interatrial septum Ductus Ateriosus Connection between pulmonary trunk and aorta Becomes ligamentum arteriosum Age related Changes Valve sclerosis build up of deposits on the valve deposition starts in youth Decreased cardiac reserve heart muscle loses its strength Fibrosis of myocardium Atherosclerosis deposition of materials inside blood vessels