BSC 2086 1st Edition Lecture 10 Outline of Last Lecture I Hemostasis Continued II Introduction to Cardiovascular System III Anatomy of the Heart Outline of Current Lecture I Myocardial Infraction II The Conducting System III Cardiac Cycle Current Lecture I Myocardial Infraction a Heart attack b Cardiac muscles die due to blockage of coronary circulation c Infarct nonfunctional area filled with dead tissues d Severe coronary artery diseases result in heart attacks e Consequences i If the blockage occurs near the start of one of the coronary arteries the damage will be widespread and the heart may stop beating ii If the blockage is in one of the smaller arterial branches the person may survive the crisis but have problems later on 1 Cardiac arrhythmias 2 Reduced contractility f Coronary thrombosis thrombus formation at a plaque i Most common cause of MI g A spasm of smooth muscle of the vascular wall can cause blockage of a vessel that is already blocked by plaque h Intense pain is similar to that of angina pectoris but continues even during rest i Pain does not always cause a heart attack j Can be diagnosed with ECG and blood studies i Elevated enzyme counts due to damaged myocardial cells show up in blood tests ii Enzymes include 1 Cardiac troponin T 2 Cardiac troponin I 3 CK MB II k Treatment i 25 die before medical assistance ii 65 of deaths in those under 50 happen 1 hour after initial infarct iii Risk factor modification 1 Stop smoking 2 Treatment for high blood pressure 3 Modifying cholesterol intakes and losing weight 4 Reducing stress 5 Increase physical activity if appropriate iv Drug treatment 1 Aspirin and Coumadin reduce coagulation and risk of thrombosis 2 Those that block sympathetic stimulation 3 Nitroglycerin cause vasodilation 4 Calcium channel blockers 5 After an MI a Those that relieve pain b Fibrinolytic agents that help dissolve clots c Oxygen v Noninvasive Surgery 1 Atherectomy catheter inserted in coronary artery to the plaque in order to increase diameter of the narrow passageway 2 Balloon angioplasty inserting catheter with an inflatable balloon at the tip a Once inside the balloon is inflated which presses the plaque against the vessel walls b A stent is then inserted vi Coronary Artery Bypass Surgery CABG 1 A small section is removed from either a small artery or peripheral veins and used to make a detour around the obstructed part of the coronary artery 2 During a single operation up to 4 coronary arteries can be rerouted The Conducting System a Heartbeat i Single contraction of the heart ii The heart contracts in a series starting with the atria and then the ventricles iii Conducting system cardiac muscle cells that control and coordinate heartbeat 1 Show automaticity by initiating the impulses to contract 2 Doesn t need input from nervous and endocrine 3 Structures a Conducting cells in myocardium i Interconnect SA and AV nodes ii Spread out stimulus in myocardium iii Internodal paths distribute stimuli to atrial muscle cells in the atrium iv AV bundles and the bundle branches spread out stimuli to ventricular myocardium through Purkinje fibers v Pacemaker potential resting potential of conducting cells 1 Gradually depolarizes toward threshold 2 Cells repolarize to resting potential and then depolarize again in rhythmic cycle 3 SA node is first to depolarize to establish heart rate b Sinoatrial SA node location of pacemaker cells in right atrium wall i Intermodal pathways connect it to AV node ii Step 1 of atrial activation c Atrioventricular AV node more pacemakers located here at the junction of atria and ventricles i Step 2 of atrial activation 1 Receives impulse from SA node ii Step 3 1 Delays impulse by about 100 msec iii Atrial contraction begins iv Contractile cells cardiac muscle cells that produce contraction that propel blood 1 Stimulus distributed by Purkinje cells 2 Make up most of heart cells b Cardiac cycle steps i Action potential from pacemaker cells at the sinoatrial SA node ii Goes through conducting system iii Makes action potentials in cardiac muscle contractile cells iv Electrocardiogram ECG or EKG can record these action potentials or electrical events c Heart Rate i SA node generates 80 100 action potentials per minute ii Parasympathetic stimulation slows down heart rate iii AV nodes generate 40 60 action potentials per minute 1 If SA node pacemakers are damaged or non function the AV node can take over iv Normal heart rate is less than 80 100 beats min due to parasympathetic innervation III d AV Bundle i In septum ii Carries impulse to left and right bundle branches which conduct Purkinje Fibers Step 4 of atrial activation e Purkinje Fibers i Step 5 distribute impulse through ventricles ii Complete atrial contraction and begin ventricular contraction f Abnormal Pacemaker Function i Bradycardia abnormally slow heart rate ii Tachycardia abnormally fast heart rate iii Ectopic pacemaker abnormal cells that make a higher rate of action potentials than the SA or AV nodes 1 Potentials can bypass conducting system and disrupt ventricular contractions g Electrocardiogram ECG or EKG i Recording of electrical events in heart obtained by electrode at specific locations of the body ii Abnormal patterns diagnose damage iii Features 1 P wave atria depolarize 2 QRS complex ventricles depolarize 3 T wave ventricles repolarize h Refractory period i Absolute refractory period long period where cardiac muscle cells cannot respond ii Relative refractory period short period where response depends on amount of stimulus iii Timing 1 Length of cardiac action potential in ventricular cell 2 250 300 msec 3 long refractory period prevents summation and tetany i Role of calcium ions i Contraction produced by an increase in Ca2 ion around myofibrils ii Arrival of extracellular Ca2 triggers release of calcium ion reserves in sarcoplasmic reticulum j Energy for contractions i Aerobic energy generated from 1 Mitochondrial breakdown of fatty acids and glucose ii Uses oxygen from hemoglobin and in myoglobin stored in cardiac muscles Cardiac Cycle a Period between start of one heartbeat and beginning of next b Systole contraction c Diastole relaxation d Phases i Atrial systole begins by forcing small amount of blood into relaxed ventricles ii Atrial systole ends and atrial diastole begins iii Ventricular systole starts with contraction pushing AV valves closed but doesn t create sufficient pressure to open semilunar valves iv Continues with rising pressure and
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