BIOL 320 1 st Edition Lecture 7 Outline of Last Lecture I Rh Factor A Homeostatic Imbalance II Developmental Aspects III Cardiovascular System A Heart Outline of Current Lecture IV Coronary Circulation A Clinical Correlations V Heart Microscopic Anatomy VI Heart Physiology A Action Potentials of Auto rhythmic Cells VII Conduction System of the Heart VIII Regulation of Heart Rate IX Electrocardiography A Normal and Abnormal ECG Tracings X Heart Dysfunction Current Lecture Coronary Circulation needs its own vascular circulation just as the rest of the body does A Left coronary artery branches a Circumflex artery b Anterior interventricular artery B Right coronary artery branches a Right marginal artery b Posterior interventricular artery C Three veins drain the heart a Small cardiac vein b Middle cardiac vein c Great cardiac vein D Coronary sinus empties into the right atrium E Terms a Anastomoses branching or merging of vessels vessel junction near major organs and joints Clinical Correlations o Angina pectoris Cause fleeting temporary blockage of coronary artery Glycolysis lactic acid pain since no oxygen is getting to cardiac muscle Treatment beta blockers blood thinners nitrates anti coagulants quit smoking get exercise diet modification and calm down to lower blood pressure o Myocardial infarction Cause serious blockage of coronary arteries Hypoxia inflammatory cells release cytokines macrophages release free radicals damage tissue o Heartburn Cause acid reflux Treatment antacids Prilosec Nexium Heart Microscopic Anatomy A Histology a Cardiac muscle cells usually mono or di nucleated still striated stretched together with endomysium and joined together by intercalated discs b Desmosomes prevent cell separation help stick together c Gap junctions where the ions pass through for electrical current firing of heart starts from the pacemaker cells B Terms a Syncytium acts as a coordinated unit because of electrical link C Facts a No true cell boundaries act as a group not individually b Heart needs to be strong slow to fatigue so lots of mitochondria 25 of cell makeup c Influenced by ANS d Refractory period is long mandatory rest so cannot be over stimulated cannot tetanize Heart Physiology Action Potential of Contractile Cardiac Muscle Cells 1 Depolarization is due to sodium ion influx through fast voltage gated sodium channels A positive feedback cycle rapidly opens many sodium channels reversing the membrane potential Channel inactivation ends this phase 2 Plateau phase is due to calcium ion influx through slow calcium channels This keeps the cell depolarized because few potassium channels are open 3 Repolarization is due to calcium channels inactivating and potassium channels opening This allows potassium ion efflux which brings the membrane potential back to its resting voltage Action Potentials of Auto rhythmic Cells 1 Pacemaker potential this slow depolarization is due to both opening of sodium channels and closing of potassium channels 2 Depolarization the action potential begins when the pacemaker potential reaches threshold Depolarization is due to calcium ion influx through calcium channels 3 Repolarization is due to calcium channels inactivating and potassium channels opening This allows potassium efflux which brings the membrane potential back to its most negative voltage o 1 of cardiac muscle cells are auto rhythmic o Slowly allow leakage of potassium efflux during refractory Conduction System of the Heart A Conduction system of the heart is the internal system for production of rhythmic contraction of the heart B SA Node main pacemaker of the heart a Stimulates both atria of the heart b Sends signals to the AV Node c Rate 70 75 beats per minute C AV Node a Delays signal received from the AV Node b If there is a problem with the SA Node AV Node can run heart but very slow as low as 40 beats per minute c Delay 0 1 second D Bundle of His a Electrical connection from atria from two nodes to the ventricles E Bundle Branches a Purkinje fibers b Fibers to papillary muscles F Order of Contraction 1 Atria 2 Papillary muscles to ensure the AV valve stays shut 3 Ventricles Regulation of Heart Rate A Sympathetic ANS a Cardio acceleratory center CAC b Innervation point both node all cardiac muscles c Neurotransmitter norepinephrine NE B Parasympathetic ANS a Cardio inhibitory center CIC b Innervation point both nodes c Cranial nerve vagus nerve X d Neurotransmitter acetylcholine ACh C Bainbridge Reflex a A sympathetic reflex initiated by increased venous return and increased atrial filling Stretching the atrial walls increases heart rate by stimulating both the SA node and the atrial stretch receptors which trigger reflexive adjustments that result in increased sympathetic stimulation of the heart D Endocrine Regulation a Epinephrine quick release from adrenal medulla brief increase in HR b Thyroxin gradual release from thyroid longer lasting increase in HR long term stress Electrocardiography A Measures electrical activity in heart B P wave atrial depolarize C QRS complex ventricles depolarize and atria repolarize D T wave ventricle repolarize E Intervals used to diagnose a variety of heart condition problems Deflection Waves of an ECG Tracing 1 Atrial depolarization initiated by the SA node causes the P wave 2 With atrial depolarization complete the impulse is delayed at the AV node 3 Ventricular depolarization begins at apex causing the QRS complex Atrial repolarization occurs 4 Ventricular depolarization is complete 5 Ventricular repolarization begins at apex causing the T wave 6 Ventricular repolarization is complete Normal and Abnormal ECG Tracings o Junctional rhythm No P waves SA node is out since it is what cause the atria to contract o Second degree heart block P wave is not getting signal through to AV node Unfollowed Ps o Ventricular fibrillation Blood is not being pumped blood is not getting to tissues carbon dioxide is not getting removed Heart Dysfunction A Arrhythmia a Characteristics irregular heart beat b Common causes caffeine nicotine B Fibrillation a Characteristics rapid irregular uncoordinated contractions b Defibrillation resets conduction system i A Fib don t get zapped with paddles patients stays for observation pacemaker inserted for atria ii V Fib get the paddles blood is not going body wide C Ectopic Focus a Characteristics non nodal pacemaker D Bradycardia a Characteristics very low HR 60 bpm b Common causes athlete fit certain drugs overactive P