VPHY 3100: Week of 10/19
VPHY 3100: Week of 10/19 VPHY 3100
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This 4 page Class Notes was uploaded by Lorin Crear on Friday October 23, 2015. The Class Notes belongs to VPHY 3100 at University of Georgia taught by Dr. Li, Dr. Wells, Dr. Brown in Summer 2015. Since its upload, it has received 102 views. For similar materials see Elements of Physiology in Animal Science and Zoology at University of Georgia.
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Date Created: 10/23/15
Chapter 13 Heart and Circulation 0 Electrical Activity of Heart and the Electrocardiogram 0 Heart composed of two types of cells I Contractile cells in ventricles and atria o 4 channels 0 fast Na channel I Voltagegated I Opens rapidly and spontaneously closes rapidly I Moves Na into cell 0 slow Ca2 channel I Voltagegated I Opens slowly and spontaneously closes slowly I Moves Ca2 into cell 0 K channel I Voltagegated I Rapidly opens and remains open until cell nears resting potential I Moves K out of cell 0 SR Ca2 release channel I Moves Ca2 out of SR into cytosol o 2 carriers 0 NaK ATPase pump I 3 Na out 2 K in o Ca2 pumps I 3 Na in 2 Ca2 out o Transmembrane potential 90 mV I Excitatorymyoconductive cells in nodes and networks 0 3 channels 0 slow Ca2 channel 0 K channel 0 HCN hyperpolarizationgated cyclic nucleotide responsive Na channel I Aka pacemaker channels I Hyperpolarizationgated 0 Opens when repolarizing cell nears resting potential 0 Opens slowly 0 Moves Na into cell causing depolarization I Cyclic nucleotide responsive o cAMP is a cyclic nucleotide o cAMP causes HCN channels to open more rapidly 0 increases rate of depolarization of cells 0 More heart anatomy Cardiac cells both contractile and excitatory are branched and interconnected by intercalated discs 0 Intercalated discs 0 Desmosome physical connection 0 Connexon gap junction channel allowing ionic conductance Sinoatrial node SA node 0 Cluster of cells in upper wall of right atrium 0 Also called pacemaker of heart 0 Has the most HCN activity I AV node area of specialized tissue between atria and ventricles that electrically connects them and Purkinje fibers also have HCN channels 0 Function as slower secondary pacemakers 0 Automaticity automatic nature of cardiac depolarization o Propagation of cardiac action potentials Originate in SA node and spread rapidly AV node only path for electrical activity from atria to ventricles 0 Due to annulus fibrosus fibrous insulation that blocks other pathways between atria and ventricles 0 AV nodal delay 0 Creates delay between atrial and ventricular depolarization o Leads to delay between atrial and ventricular contraction After passing through AV node conduction is rapid in Bundle of His aka Common Bundle Branch and rest of excitatory ventricular cells 0 ExcitationContraction Coupling Delay between excitation and contraction 0 Contraction begins during absolute refractory period 0 Peak contraction right before relative refractory period Ca2 diffuses into cells via slow calcium channels Ca2 stimulates opening of Ca2 channels on SR Ca2 from SR binds to troponin to stimulate power strokes Ca2 is actively transported back into SR or out of cell Contractile cell relaxes o Electrocardiogram ECGEKG Recording of electric activity of heart Measured on surface of body Picks up movement of ions in body tissues in response to electric activity Does NOT record action potentials or contractions but can indicate when these occur Waves and intervals 0 P wave atrial depolarization 0 Returns to isoelectric line as action potential moves through AP node 0 QRS complex ventricular depolarization o T wave ventricular repolarization I Einthoven s triangle 0 System for recording EKG 0 Three different ways called leads of connecting Wires to body 0 Blood pressure 0 Systemic arterial blood pressure aka blood pressure or BP I Systolic BPdiastolic BP 120 mmHg80 mmHg I Average mean BP or MBP 100 mmHg 0 Systemic organs and tissues count on BP to be held at relatively constant value 0 MBP cardiac output CO X TSVR total systemic vascular resistance 0 Cardiac output volume of blood pumped per minute by left ventricle I heart rate X stroke volume 0 MBP HR X SV X TSVR 0 Changing heart rate HR I Chronotrope any factor that alters heart rate I HR determined by ratio of sympathetic parasympathetic stimulation of SA node 0 Sympathetic nerve effects 0 Release of epinephrine and norepinephrine enhances opening of HCN channels 0 Causes eXCitatory cells to reach threshold faster 0 Increases heart rate 0 positive chronotrope 0 Parasympathetic nerve effects 0 Release of acetylcholine enhances opening of K channels 0 Causes eXCitatory cells to reach threshold slower o Reduces heart rate 0 negative chronotrope 0 Changing stroke volume SV I Inotrope any factor that alters stroke volume I Stroke volume determined by 0 Preload o enddiastolic volume stretch before contraction o FrankStarling Law of the Heart I More blood presented to chamber of the heart more blood ejected I Increased preload is a positive inotrope 0 Contractility of myocardium o Contractility strength of contraction o Controlled by sympathetic stimulation of myocardia 0 Quick way to affect SV and therefore MBP o Afterload 0 Opposition to ejection through the aortic valve 0 Normally has little effect on SV except in the case of some cardiovascular disease Preload enddiastolic volume stretch before contraction 0 Changing TSVR total systemic vascular resistance Arterioles control TSVR Small Innervated and respond to localhumoral stimuli Diameter can be adjusted Control of TSVR o All tissues have some ability to control diameter of their own arterioles o Called intrinsic control of resistance 0 Vital tissues heart brain kidneys have very effective intrinsic control and only respond to local signals not ANS 1 Increased tissue metabolic rate 2 Release of vasodilators 3 Relaxation of arteriolar smooth muscle 4 Decreased arteriolar resistance 5 Increased blood ow to that tissue 0 Extrinsic Control of Resistance 0 By sympathetic division of ANS o Nonvital tissues e g skin abdominal viscera more affected by this mechanism than vital tissues 0 Skeletal muscle behaves like nonvital tissue When at rest and vital tissue during exercise TSVR controlled by combination of intrinsic and extrinsic signals 0 Arterial baroreceptor system Minimizes variations in MBP throughout the day Receptors in aortic arch sense stretch When blood pressure deviates from 100 mmHg Changes in HR SV and TSVR are stimulated to oppose variation in MBP Neurologic control system Uses ANS
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