The Heart: Anatomy and Function - PDF

The Heart ANT 318 1  The Heart Circulates blood About the size of the fist – 250 – 350 grams Enclosed in the mediastinum 2/3 lie left of the midsternal line Extends from the 2nd rib to the 5th intercostal space...

The Heart ANT 318 1  The Heart Circulates blood About the size of the fist – 250 – 350 grams Enclosed in the mediastinum 2/3 lie left of the midsternal line Extends from the 2nd rib to the 5th intercostal space 2  The Heart Coverings Enclosed by the pericardium 2 layers - Fibrous pericardium - Serous pericardium 3  The Heart Fibrous Pericardium Protects the heart Anchors the heart to surrounding structures Prevents over filling of the heart 4  The Heart Serous Pericardium Parietal pericardium – Lines internal surface of fibrous pericardium Pericardial cavity – Slit-like cavity between the visceral and parietal layer Visceral pericardium – Covers the external surface of the heart – Also known as the epicardium 5 Layers of the Heart Epicardium Myocardium Endocardium 6  Layers of the Heart Epicardium Visceral layer of the serous pericardium Often infiltrated with fat 7  Myocardium Cardiac muscle – Tissues fibers arranged in spirals/circular bundles Fibrous skeleton – Network of collagen and elastin fibers – Provides additional support to heart/great vessels and the valves – Anchors the cardiac muscles – Serves as electrical insulator between atria and ventricles 8  Layers of the Heart Endocardium Glistening white sheet of endothelium Continuous with the endothelial lining of the blood vessels 9  Heart Anatomy Four chambers – Right and left atria (RA, LA) top, receiving chambers Left atrium – Right and left ventricles (RV, LV) bottom, larger, pumping Right atrium chambers Separated by a septum – Interatrial septum – Interventricular septum Right ventricle Frontal section Left ventricle  Valves Atrioventricular Direction of blood flow valves Atrium – Located BETWEEN Cusp of atrioventricular valve (open) atria and Chordae ventricles tendineae AV valves open Papillary muscle when pressure is greater in atria Atrium AV valves close Cusps of atrioventricular valve (closed) when pressure is Blood in greater in ventricle ventricles  Valves Semilunar valves – Located BETWEEN ventricles and large arteries Semilunar valves open when pressure is greater in ventricles Semilunar valves close when pressure is greater in arteries Superior View of Valves Blood flow Which side has Capillary beds through the of lungs where thicker walls? gas exchange heart occurs Why? Pulmonary Circuit Pulmonary Pulmonary arteries veins Aorta and Venae branches cavae Left atrium Left Right ventricle atrium Right Heart ventricle Systemic Circuit Capillary beds Oxygen-rich, CO2-poor blood of all body Pathway of blood flow tissues where gas Oxygen-poor, exchange occurs through the heart video 14 CO2-rich blood  The Heart Cardiac Muscle Fibers Cardiomyocytes Striated, single nucleus Cells are short, fat, branched, and interconnected  Cardiac Muscle Fibers Functional Structural Membranes interlock with adjacent fibers – junctions are called intercalated discs – Contain desmosomes and gap junction – Myocardium acts as a single coordinated unit 16  Contraction Cardiac vs Skeletal Means of Stimulation – Skeletal muscle is innervated by a nerve – Cardiac muscle has self excitable tissue that cycle, producing automaticity Organ vs Motor Unit Contraction – In a skeletal muscle, not all muscle fibers contract with each impulse… only the motor unit that is stimulated – Either all cardiac fibers contract as unit, or none do (gap junctions) Refractory Period – Inexcitable period when Na+ channels are still open or inactivated – Cardiac lasts 250 ms (as long as the contraction) – Skeletal lasts 15 ms But both are triggered by action potential 17  Electrical Events of the Heart Controlled both intrinsically… – Beating is determined without nervous system innervation – Properties of the heart itself – Intrinsic heart rate (HR): 100 beats/min Observed in patients lacking extrinsic innervation …And extrinsically – Autonomic nervous systems acts on the heart to alter intrinsic rate Together, observed normally as 70-80 beats/min – Sinus rhythm (average) Cardiac Conduction System Spontaneous rhythmicity (autorhythmicity) – Sinoatrial (SA) node – Atrioventricular (AV) node – AV bundle (bundle of His) – Right and left bundle branches – Subendocardial conducting network (Purkinje fibers) – From SA node initiation to contraction in ~0.22s Electrical signal spreads via gap junctions  Cardiac Conduction System 1. Sinoatrial (SA) node: initiates contraction signal – Pacemaker cells in upper posterior RA wall Depolarize FASTER than rest of myocardium – Signal spreads from SA node via RA/LA to AV node = atrial contraction  Cardiac Conduction System 2. Atrioventricular (AV) node: delays, relays signal to ventricles – In inferior interatrial septum – Delay (0.13s) allows RA, LA to contract before RV, LV resulting in longer filling time – Then relays signal to AV bundle  Cardiac Conduction System 3. AV bundle (bundle of His): relays signal to RV, LV – Travels along interventricular septum – Only electrical connection between atria and ventricles – Divides into …. 4. Right and left bundle branches – Sends signal toward apex of heart  Cardiac Conduction System 5. Purkinje fibers (subendocardial conducting network): send signal into RV, LV – Terminal branches of bundle branches – Spread throughout entire ventricle walls – Stimulate RV, LV contraction from apex towards atria  Cardiac Conduction System Overview Cardiac conduction system video  Pacemaker and Action Potentials Pacemaker cells in the heart – SA node has unstable resting membrane potential – Spontaneously changing MPs = pacemaker potentials  Pacemaker and Action Potentials Unstable resting potential “Pacemaker Potential” Threshold K+ channels closed from Membrane potential (mV) +10 previous AP 0 –10 Slow depolarization –20 caused by open Na+ –30 channels –40 –50 –60 Pacemaker Na+ –70 potential Time (ms) Pacemaker Cell K+ © 2013 Pearson Education, Inc.  Pacemaker and Action Potentials Action Potential Threshold met at -40 Threshold mV +10 Action Membrane potential (mV) potential 0 Rapid depolarization –10 due to Calcium Influx –20 through voltage gated –30 Ca+ channels –40 –50 Activated at -40mV –60 –70 Ca2+ Time (ms) Pacemaker Cell © 2013 Pearson K+ Education, Inc.  Pacemaker and Action Potentials Repolarization (when 0 m met) Inactivation of Ca+ channels Activation of K+ channels Membrane potential (mV) +10 Repolarization 0 –10 Na+ Ca2+ –20 –30 –40 –50 Pacemaker –60 Cell –70 K+ Time (ms) …Pacemaker potential starts over © 2013 Pearson Na+ begin leaking again Education, Inc. Were always open!  Electrocardiogram (ECG) SA node sets off heartbeat – Typically fires every 0.8 seconds – Resting rate at 75 bpm ECG or EKG: recording of heart’s electrical activity – Diagnostic tool Three basic phases – P wave: atrial depolarization – QRS complex: ventricular depolarization – T wave: ventricular repolarization  Sequence of depolarization and repolarization of the heart to the deflection waves of an ECG  Cardiac Cycle One complete contraction and relaxation of all four chambers of the heart Diastole Systole  Heart Sounds Auscultation—listening to sounds made by body First heart sound – Louder and longer “lubb” – Closure of AV valves Second heart sound – Softer and sharper “dupp” – Closure of semilunar valves —rarely heard in people over 30  Wigger’s Copyright © McGraw-Hill Education. Permission required for reproduction or display. Diastole Systole Diastole 120 Aortic Diagram pressure 100 Pressure (mm Hg) 80 Aortic Aortic valve valve Left closes 6 opens ventricular (dicrotic notch) 0 pressure AV 40 valve AV Left atrial valve closes 20 pressure opens Cardiac Cycle 0 120 End-diastolic volume (mL) Actions Ventricular volume 90 60 End-systolic volume – Blood Flow Direction P R T P R ECG – Chambers Q S Q S – Valves Heart sounds S2 S3 S1 S2 S3 S1 Sounds Phase of cardiac cycle 1a 1b 1c 2 3 4 1a 1b 1c 2 0.2.4.6.8.2.4 Electrical activity Time (seconds) Ventricular filling 2 3 4 1a Rapid filling 1c Atrial systole Isovolumetric Ventricular Isovolumetric Blood Volume 1b Diastasis contraction ejection relaxation Blood Pressure  Wigger’s Copyright © McGraw-Hill Education. Permission required for reproduction or display. Diastole Systole Diastole 120 Aortic Diagram pressure 100 Pressure (mm Hg) Ventricular filling 80 Aortic Aortic valve valve Left closes – 6 opens ventricular (dicrotic notch) Ventricles expand and their 0 40 pressure AV AV valve pressure drops below that of 20 Left atrial pressure closes valve opens the atria 0 120 End-diastolic volume (mL) – AV valves open and blood Ventricular volume 90 flows into the ventricles 60 End-systolic volume R R T P P ECG (1a) Rapid filling Q Q S S Heart (1b) Diastasis sounds S2 S3 S1 S2 S3 S1 – P wave at end Phase of cardiac cycle 1a 1b 1c 2 3 4 1a 1b 1c 2 0.2.4.6.8.2.4 – Atrial depolarization Time (seconds) Ventricular filling 2 3 4 (1c) Atrial systole 1a Rapid filling 1b Diastasis 1c Atrial systole Isovolumetric contraction Ventricular ejection Isovolumetric relaxation – End-diastolic volume – Each ventricle contains about 130 mL of blood  Wigger’s Copyright © McGraw-Hill Education. Permission required for reproduction or display. Diastole Systole Diastole 120 Aortic Diagram pressure 100 Pressure (mm Hg) Isovolumetric contraction 80 Left Aortic valve opens Aortic valve closes 6 ventricular (dicrotic notch) – Atria repolarize, relax and 0 pressure AV 40 valve AV Left atrial valve closes remain in diastole for rest of 20 0 pressure opens cardiac cycle End-diastolic 120 volume (mL) Ventricular – Ventricles depolarize, 90 volume causing QRS complex, and 60 End-systolic volume R R begin to contract P T P – AV valves close as ECG Q Q ventricular blood surges S S back against the cusps Heart sounds Heart sound occurs at S2 S3 S1 S2 S3 S1 the beginning of this Phase of cardiac cycle 1a 1b 1c 2 3 4 1a 1b 1c 2 phase 0.2.4.6.8.2.4 Time (seconds) Ventricular filling “Isovolumetric” because 1a Rapid filling 1b Diastasis 1c Atrial systole 2 Isovolumetric contraction 3 Ventricular ejection 4 Isovolumetric relaxation although ventricles contract, they do not eject blood – Aorta/pulmonary trunk pressure still greater than ventricles  Wigger’s Copyright © McGraw-Hill Education. 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Diastole Systole Diastole 120 Aortic Diagram pressure 100 Pressure (mm Hg) Ventricular ejection 80 Aortic valve Aortic valve – Ventricular pressure exceeds Left closes 6 opens ventricular (dicrotic notch) 0 pressure AV arterial pressure - semilunar 40 Left atrial valve closes AV valve valves open 20 0 pressure opens – First: rapid ejection—blood 120 End-diastolic volume (mL) Ventricular volume spurts out of ventricles quickly 90 – Then: reduced ejection—slower 60 End-systolic volume R R flow with lower pressure P T P – T wave of ECG occurs late in this ECG Q Q S S phase Heart Ventricular repolarization sounds S2 S3 S1 S2 S3 S1 Phase of 1a 1b 1c 2 3 4 1a 1b 1c 2 cardiac cycle Ventricles don’t expel all blood 0.2.4.6.8 Time (seconds).2.4 – Stroke volume (SV) is about 70 Ventricular filling 2 3 4 mL 1a Rapid filling 1b Diastasis 1c Atrial systole Isovolumetric contraction Ventricular ejection Isovolumetric relaxation Amount ejected – 60 mL remaining blood is end- systolic volume (ESV) ESV = EDV - SV  Wigger’s Copyright © McGraw-Hill Education. 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Diastole Systole Diastole 120 Aortic Diagram pressure 100 Pressure (mm Hg) Isovolumetric relaxation 80 Aortic valve Aortic valve Left closes 6 opens ventricular – T wave ends and ventricles begin (dicrotic notch) 0 pressure AV 40 valve AV to expand 20 Left atrial pressure closes valve opens – Blood from aorta and pulmonary 0 trunk briefly flows backward 120 End-diastolic volume (mL) Ventricular volume filling cusps and closing 90 semilunar valves 60 End-systolic volume R R Creates pressure rebound that T P P appears as dicrotic notch in ECG graph of artery pressure Q S Q S Heart sound occurs Heart sounds “Isovolumetric” because S2 S3 S1 S2 S3 S1 semilunar valves are closed Phase of cardiac cycle 1a 1b 1c 2 3 4 1a 1b 1c 2 and AV valves have not yet 0.2.4.6.8 Time (seconds).2.4 opened Ventricular filling – Ventricles are therefore taking in 1a Rapid filling 1c Atrial systole 2 Isovolumetric 3 Ventricular 4 Isovolumetric 1b Diastasis contraction ejection relaxation no blood When AV valves open, ventricular filling begins again