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FSU BSC 2086 - The Heart

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BSC 2086 1st Edition Lecture 10 Outline of Last Lecture I. Hemostasis ContinuedII. Introduction to Cardiovascular SystemIII. Anatomy of the Heart Outline of Current Lecture I. Myocardial InfractionII. The Conducting System III. Cardiac CycleCurrent LectureI. Myocardial Infraction a. Heart attackb. Cardiac muscles die due to blockage of coronary circulation c. Infarct: nonfunctional area filled with dead tissuesd. 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 beatingii. If the blockage is in one of the smaller arterial branches the person may survive the crisis but have problems later on1. Cardiac arrhythmias 2. Reduced contractility f. Coronary thrombosis: thrombus formation at a plaquei. Most common cause of MIg. A spasm of smooth muscle of the vascular wall can cause blockage of a vessel that is already blocked by plaqueh. Intense pain is similar to that of angina pectoris but continues even during rest i. Pain does not always cause a heart attackj. Can be diagnosed with ECG and blood studiesi. Elevated enzyme counts due to damaged myocardial cells show up in blood testsii. Enzymes include:1. Cardiac troponin T,2. Cardiac troponin I, 3. CK-MB k. Treatment:i. 25% die before medical assistance ii. 65% of deaths in those under 50 happen 1 hour after initial infarctiii. Risk factor modification:1. Stop smoking2. Treatment for high blood pressure3. Modifying cholesterol intakes and losing weight4. Reducing stress5. Increase physical activity if appropriate iv. Drug treatment:1. Aspirin and Coumadin: reduce coagulation and risk of thrombosis2. Those that block sympathetic stimulation3. Nitroglycerin: cause vasodilation4. Calcium channel blockers5. After an MIa. Those that relieve painb. Fibrinolytic agents that help dissolve clotsc. Oxygenv. Noninvasive Surgery1. Atherectomy: catheter inserted in coronary artery to the plaque inorder to increase diameter of the narrow passageway 2. Balloon angioplasty: inserting catheter with an inflatable balloon at the tipa. 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 peripheralveins 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 reroutedII. The Conducting System a. Heartbeat i. Single contraction of the heartii. The heart contracts in a series starting with the atria and then the ventriclesiii. Conducting system: cardiac muscle cells that control and coordinate heartbeat1. Show automaticity by initiating the impulses to contract 2. Doesn’t need input from nervous and endocrine 3. Structures:a. Conducting cells- in myocardiumi. Interconnect SA and AV nodesii. Spread out stimulus in myocardiumiii. Internodal paths distribute stimuli to atrial muscle cells in the atriumiv. AV bundles and the bundle branches spread out stimuli to ventricular myocardium through Purkinje fibers v. Pacemaker potential: resting potential of conducting cells1. Gradually depolarizes toward threshold2. Cells repolarize to resting potential and thendepolarize 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 walli. Intermodal pathways connect it to AV nodeii. 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 activation1. Receives impulse from SA nodeii. Step 31. Delays impulse by about 100 mseciii. Atrial contraction begins iv. Contractile cells: cardiac muscle cells that produce contraction that propelblood 1. Stimulus distributed by Purkinje cells 2. Make up most of heart cells b. Cardiac cycle stepsi. Action potential from pacemaker cells at the sinoatrial (SA) nodeii. Goes through conducting systemiii. Makes action potentials in cardiac muscle contractile cellsiv. 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 rateiii. 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 innervationd. AV Bundle i. In septumii. Carries impulse to left and right bundle branches which conduct Purkinje Fibers (Step 4 of atrial activation)e. Purkinje Fibersi. Step 5 – distribute impulse through ventriclesii. Complete atrial contraction and begin ventricular contraction f. Abnormal Pacemaker Functioni. Bradycardia: abnormally slow heart rateii. Tachycardia: abnormally fast heart rateiii. 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 bodyii. 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 cannotrespondii. Relative refractory period: short period where response depends on amount of stimulus iii. Timing:1. Length of cardiac action potential in ventricular cell2. 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 reticulumj. Energy for contractionsi. Aerobic energy generated from:1. Mitochondrial breakdown of fatty acids and glucoseii. Uses oxygen from hemoglobin and in myoglobin stored in cardiac musclesIII. Cardiac Cycle a. Period between start of one heartbeat and beginning of next b. Systole  contractionc. 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


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FSU BSC 2086 - The Heart

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