Lecture 11 Heart COVID (4) PDF

Fluid & Transport Part 2 Organization of the Cardiovascular System Heart: ̶pump Blood vessels: ̶conducting system Blood: ̶fluid medium The Heart Heart 4 Chambers: ̶2 atria:  right and left  thin-walled  separated by interatrial septum ̶2 ventricles :  right and l...

Fluid & Transport Part 2 Organization of the Cardiovascular System Heart: ̶pump Blood vessels: ̶conducting system Blood: ̶fluid medium The Heart Heart 4 Chambers: ̶2 atria:  right and left  thin-walled  separated by interatrial septum ̶2 ventricles :  right and left  thicker wall  separated by inteventricular septum Blood Circulation Systemic circulation: ̶carries blood to and from the body Pulmonary circulation: ̶carries blood to and from lungs Blood alternates between the 2 circuits Heart Chambers & Circulation Right atrium: ̶collects blood from systemic circuit Right ventricle: ̶pumps blood to pulmonary circuit Left atrium: ̶collects blood from pulmonary circuit Left ventricle: ̶pumps blood to systemic circuit Blood Vessels Arteries: ̶carry blood from the heart to tissues Veins: ̶carry blood back to the heart Capillaries: ̶networks between arteries and veins Location of the Heart Located in the mediastinum within the thoracic cavity Mediastinum Central part of the thoracic cavity Bounded by: ̶anterior – sternum ̶posterior – thoracic vertebrae ̶both sides – right & left lungs & pleurae Regions: Contents: All thoracic organs except ̶heart & its vessels, esophagus, trachea, phrenic & cardiac nerves, thoracic duct, thymus gland & mediastinal lymph nodes the lungs Location of the Heart Located in the mediastinum within the thoracic cavity Directly behind sternum Slightly to the left Between 2 lungs Pericardial sac: ̶tough fibrous tissue layer surrounds and stabilizes the heart Surface Anatomy of the Heart Base: ̶ superior end of the heart ̶ connected to the great vessels Apex: ̶ pointed tip ̶ located in the 5th left intercostal space just inside the midclaviular line Layers of the Heart Wall Pericardium: Myocardium Pericardial cavity Parietal pericardium (cardiac muscle tissue) Dense fibrous layer outer layer Cardiac muscle cells Areolar tissue Pericardium Connective tissues Myocardium: Mesothelium Artery middle layer Vein Endocardium: Endocardium Epicardium Endothelium (visceral inner layer Areolar tissue pericardium) Mesothelium Areolar tissue l rt wal He a Pericardium ou s 2 Layers: Ser rane m b ̶ parietal pericardium: me  outer layer  attached to the pericardial sac visceral pericardium (epicardium):  inner layer  attached to the heart Pericardial cavity: ̶ between the 2 layers ̶ contains pericardial fluid (15 – 50 ml) Pericardium ou s 2 Layers: Ser rane m b ̶ parietal pericardium: me  outer layer Pericardial Parietal  attached to the pericardial sac cavity pericardium Dense fibrous layer visceral pericardium (epicardium): Areolar tissue Mesothelium  inner layer Artery  attached to the heart Vein Pericardial cavity: Epicardium (visceral pericardium) ̶ between the 2 layers Mesothelium Areolar tissue ̶ contains pericardial fluid (15 – 50 ml) t wal l ea r H Myocardium Thickest layer of the heart Muscular wall Concentric layers of cardiac muscle tissue Divided into: ̶atrial myocardium ̶ventricular myocardium Composed of cardiomyocytes Characteristics of Cardiomyocytes Cardiac muscle tissue LM × 575 Small Cardiac muscle cell (intact) Intercalated disc Involuntary (sectioned) Mononucleated Striated Branching interconnections between cells Intercalated discs Cardiac muscle cell (sectioned) Have short and wide T tubules Myofibrils SR has no terminal cisternae Entrance to T tubule Sarcolemma Have no triads Mitochondrion Aerobic (high in myoglobin, mitochondria) Have intercalated discs Contact of sarcoplasmic reticulum with T tubule Sarcoplasmic Myofibrils reticulum Intercalated Discs Specialized contact points that Join adjacent cardiomyocytes (gap junctions, desmosomes) Functions: ̶maintain structure ̶conduct action potentials ̶link heart cells mechanically, chemically and electrically:  heart works like a single, fused mass of cells Cardiac vs. Skeletal Muscle Cells Endocardium Innermost layer of the heart Lines the inner surface of the heart including heart valves Simple squamous epithelium Continuous with endothelium of the great vessels Diseases of the Cardiac Wall Carditis = inflammation of the heart: ̶pericarditis ̶myocarditis pancarditis (e.g., Rheumatic Fever) ̶endocarditis Pericardial effusion: ̶abnormal accumulation of fluid in the pericardial cavity Myocardial ischemia: see CAD …  Left subclavian artery Left common carotid artery Arch of aorta Brachiocephalic Ligamentum Superficial Surface of the Heart trunk arteriosum Ascending Descending aorta aorta Left pulmonary Superior artery vena cava Pulmonary Auricle trunk of right Right Auricle of Coronary sulcus: atrium atrium left atrium Fat and vessels in anterior Right interventricular ̶ divides atria and ventricles Fat and vessels in ventricle sulcus Left coronary ventricle Anterior and posterior interventricular sulci: sulcus ̶ separate left and right ventricles Anterior View Contain blood vessels of cardiac muscle Left pulmonary artery Left pulmonary veins Arch of aorta Right pulmonary artery Fat and vessels Superior in coronary vena cava sulcus Left atrium Coronary Right sinus pulmonary veins Right (superior Left atrium and inferior) ventricle Inferior Right vena cava ventricle Fat and vessels in posterior interventricular sulcus Posterior View  Internal Anatomy of the Heart Brachiocephalic trunk Left common carotid artery Left subclavian artery Ligamentum arteriosum Superior Pulmonary trunk Aortic arch vena cava Pulmonary valve Right pulmonary Left pulmonary arteries arteries Ascending aorta Left pulmonary Fossa ovalis veins Left Opening of atrium coronary sinus Interatrial septum Aortic valve Right atrium Cusp of left AV Pectinate muscles (mitral) valve Conus arteriosus Left ventricle Cusp of right AV (tricuspid) valve Chordae tendineae Interventricular ? septum n Papillary muscles ec ti o Right ventricle Trabeculae S carneae h at Inferior vena cava W Moderator band Descending aorta  POSTERIOR Heart Valves Cardiac Left AV (bicuspid) valve (open) Pulmonary skeleton veins RIGHT LEFT VENTRICLE VENTRICLE LEFT ATRIUM Left AV (bicuspid) valve (open) One-way valves: Chordae Aortic valve tendineae (loose) (closed) Right AV Papillary muscles (tricuspid) (relaxed) ̶ permit blood flow in one direction valve (open) Aortic valve LEFT VENTRICLE (closed) (relaxed and filling ̶ prevent backflow with blood) Pulmonary ANTERIOR valve (closed) Anatomy: Ventricles are relaxed ̶ Valve cusps (leaflets): Aortic valve closed Right AV Cardiac Left AV (tricuspid) valve skeleton (bicuspid) valve  fibrous flaps guard the valve openings (closed) (closed) LEFT RIGHT Aorta LEFT VENTRICLE ATRIUM VENTRICLE ̶ All heart valves are tricuspid (3 Aortic sinus Left AV (bicuspid) valve (closed) cusps) EXCEPT mitral valve Aortic valve (open) Chordae tendineae (tense) (bicuspid, 2 cusps!) Papillary muscles (contracted) ̶ Chordae tendineae attach free Aortic valve (open) Left ventricle (contracted) cusp edges to papillary muscles of Pulmonary valve (open) ventricle Ventricles are contracting Aortic valve open  POSTERIOR Valve Groups Cardiac Left AV (bicuspid) skeleton valve (open) RIGHT LEFT VENTRICLE VENTRICLE 2 atrioventricular (AV) valves: Right AV (tricuspid) valve (open) ̶each between an atrium and a ventricle Aortic valve (closed) Pulmonary ANTERIOR valve (closed) Ventricles are relaxed 2 semilunar valves: Aortic valve closed Right AV Cardiac Left AV (tricuspid) valve skeleton ̶each between a ventricle and a great artery (bicuspid) valve (closed) (closed) LEFT RIGHT VENTRICLE VENTRICLE Aortic valve (open) Pulmonary valve (open) Ventricles are contracting Aortic valve open  POSTERIOR Atrioventricular (AV) Valves Cardiac Left AV (bicuspid) skeleton valve (open) RIGHT LEFT VENTRICLE VENTRICLE Permit blood flow from atria to Right AV (tricuspid) ventricles valve (open) Aortic valve (closed) Tricuspid valve: ANTERIOR Pulmonary valve (closed) ̶ connects right atrium to right ventricle Ventricles are relaxed Aortic valve closed Mitral (bicuspid) valve: Right AV (tricuspid) valve Cardiac skeleton Left AV (bicuspid) valve (closed) (closed) ̶ connects left atrium to left ventricle RIGHT VENTRICLE LEFT VENTRICLE Blood pressure closes valve cusps during ventricular contraction Papillary muscles tense chordae Aortic valve (open) Pulmonary tendineae: valve (open) Ventricles are contracting ̶ prevent valves from swinging into atria Aortic valve open Semilunar Valves Permit blood flow from ventricles to great vessels Pulmonary valve: ̶between right ventricle and pulmonary artery Aortic valve closed Aortic valve: ̶between left ventricle and aorta NO chordae tendineae Aortic valve open Valve Lesions Regurgitation (incompetence): ̶backflow of blood into the opposite direction ̶due to failure of valves to close properly Stenosis: ̶decreased blood flow through a valve ̶due to narrowing of valve opening Causes: ̶e.g., congenital - rheumatic fever - … Pathway of Blood Circulation Veins of the systemic circulation superior & inferior venae cavae right atrium tricuspid valve right ventricle pulmonary valve pulmonary trunk right & left pulmonary arteries right & left lungs right & left pulmonary veins left atrium mitral valve left ventricle aortic valve aorta arteries of the systemic circulation capillaries different body tissues Foramen Ovale Opening through interatrial septum Connects the 2 atria before birth Seals off at birth fossa ovalis Failure to close ASD (Atrial Septal Defect)  Right vs. Left Ventricle RV LV Right Left Ventricle Ventricle Size Smaller Larger Wall Thinner Thicker Cavity Pouch Round shape* Less More Power Less More IV Pressure * Both ventricles hold same volume of blood Connective Tissue Fibers of the Heart Physically support cardiac muscle fibres Distribute forces of contraction Add strength and prevent overexpansion of heart Elastic fibres return heart to original shape after contraction Blood Supply to the Heart (Coronary Circulation) Supplies blood to muscle tissue of heart Coronary arteries and veins Anterior Posterior view view Coronary Arteries Right and left Originate at aortic sinuses High blood pressure, elastic rebound forces blood through coronary arteries during diastole (in- between contractions) Right Coronary Artery Supplies blood to: ̶ right atrium  sinoatrial (SA) node  atrioventricular (AV) node ̶ right ventricle ̶ part of left ventricle Branches: ̶ marginal artery (ies)  across surface of right ventricle ̶ posterior descending (interventricular) artery  supplies the posterior part of interventricular septum Left Coronary Artery Supplies blood to: ̶left atrium ̶left ventricle ̶interventricular septum Branches: ̶circumflex artery ̶anterior descending (interventricular) artery  supplies the interventricular septum Coronary Anastomoses Between: circumflex and right coronary arteries anterior and posterior interventricular arteries Stabilize blood supply to cardiac muscle Coronary (Cardiac) Veins Anterior cardiac veins: ̶empty into right atrium Posterior, middle, and small cardiac veins: ̶empty into great cardiac vein or coronary sinus Great cardiac vein: ̶drains area of anterior interventricular artery ̶empties into coronary sinus Coronary sinus: ̶empties into right atrium Coronary Artery Disease (CAD) Narrowing or blocking of coronary arteries  coronary blood flow (ischemia)  O2 supply to the heart Atherosclerosis is the most common cause Coronary Artery Disease (CAD) Manifestations: ̶asymptomatic ̶angina pectoris:  sudden onset of chest pain due to myocardial ischemia ̶myocardial infarction:  necrosis of part of the heart muscle ̶sudden death Physiological Characteristics of Cardiac Tissue Automaticity: ̶ contraction without neural stimulation ̶ controlled by pacemaker cells Contractibility: ̶ controlled by autonomic nervous system ̶ extended contraction time (10X skeletal muscles) Conductivity: ̶ through intercalated discs Excitability: ̶ prevention of wave summation and tetanic contractions by cell membranes Heartbeat Single contraction of the heart The entire heart contracts in series: first the atria then the ventricles Types of Cardiac Muscle Cells Contractile cells: ̶produce contractions Conducting cells: ̶modified cardiomyocytes ̶control and coordinate heartbeat Conducting System A system of specialized cardiac muscle cells: ̶initiates and distributes electrical impulses that stimulate contraction +20 mV Sinoatrial (SA) node 0 mV Internodal −20 mV pathways Threshold −40 mV Atrioventricular −60 mV (AV) node AV bundle 0 0.8 1.6 Time (sec) Bundle Changes in the membrane potential of a pacemaker branches cell in the SA node that is establishing a heart rate Purkinje of 72 beats per minute. fibers The Conducting System Structures of the Conducting System Sinoatrial (SA) node Internodal pathways Atrioventricular (AV) node AV bundle (bundle of His) Bundle branches Purkinje fibers Structures of the Conducting System Sinoatrial (SA) node Internodal pathways Atrioventricular (AV) node AV bundle (bundle of His) Bundle branches Purkinje fibers Impulse Conduction Through the Heart Sinoatrial (SA) Node Pacemaker of the heart Depolarizes first, establishing heart rate Generates 80–100 action potentials per minute (AV node generates 40–60) Heart Rate (HR) Number of heartbeats/minute Normal range = 60–90/min: slightly slower than the SA node rate modified by autonomic activity, hormones, and other factors Abnormal Pacemaker Function Bradycardia: ̶ abnormally slow heart rate (< 60/min) Tachycardia: ̶ abnormally fast heart rate (> 90/min) Ectopic pacemaker: ̶ abnormal cells outside the SA node ̶ generate high rate of action potentials ̶ bypass conducting system ̶ disrupt ventricular contractions Sick sinus syndrome Action Potential in The Cardiac Muscle Resting Potential Of a ventricular cell: about —90 mV Of an atrial cell: about —80 mV Steps of Cardiac Action Potential 1. Rapid depolarization (Na entry): ̶ Na (fast) channels open ̶ Na+ ions enter cardiomyocytes 2. Plateau (Ca entry/Na loss): ̶ Na channels close ̶ Ca (slow) channels open ̶ Ca++ ions enter cardiomyocytes ̶ Na+ ions pumped out ̶ hold membrane at 0 mV Steps of Cardiac Action Potential 3. Repolarization (K loss): ̶ Ca channels close ̶ K (slow) channels open ̶ K+ ions exit cardiomyocytes ̶ resting potential is restored ̶ K channels close at the end Refractory Periods Absolute refractory period: cardiomyocytes cannot respond long Relative refractory period: cardiomyocytes respond only to strong stimuli short Duration of Cardiac Action Potential 250–300 msec: ̶30 times longer than skeletal muscle fiber ̶long refractory period prevents summation and tetany Ca2+ & Myocardial Contraction Contraction of a cardiac muscle cell is produced by an increase in Ca2+ concentration around myofibrils Cardiac muscle tissues are very sensitive to changes in Ca 2+ concentrations Electrocardiogram (ECG - EKG) Recording of electrical events in the heart Obtained by electrodes at specific body locations Can reflect cardiac abnormalities Features of ECG P wave: ̶ atria depolarize QRS complex: ̶ ventricles depolarize T wave: ̶ ventricles repolarize P–R interval: ̶ from start of atrial depolarization ̶ to start of QRS complex Depolarization = Q–T interval: contraction = systole ̶ ventricular depolarization and Replarization = ̶ ventricular repolarization relaxation = diastole ECG Waves Timing Normal ECG Tracing Abnormal ECG Ischemic heart disease: angina myocardial infarction Chamber enlargement: e.g., Rt or Lt ventricular hypertrophy Electrolyte disturbances: e.g., hyperkalemia - hypercalcaemia Cardiac dysrhythmias... Cardiac Dysrhythmias Abnormal patterns of cardiac electrical activity Normal ECG Abnormal ECG Cardiac Cycle Cardiac Cycle Period from beginning of 1 heartbeat to beginning of the next Each cardiac cycle includes: systole (contraction):  atrial systole  ventricular systole diastole (relaxation):  atrial diastole  ventricular diastole Cardiac Cycle & Pressure Blood Pressure in any chamber: rises during systole falls during diastole Blood flows from high to low pressure: controlled by timing of contractions directed by one-way valves Cardiac Cycle & Heart Rate At 75 beats per minute: cardiac cycle lasts about 800 msec When heart rate increases: all phases of cardiac cycle shorten, particularly diastole 4 Main Events of Cardiac Cycle 1. Atrial systole 2. Atrial diastole 3. Ventricular systole 4. Ventricular diastole Phases of The Cardiac Cycle 1. Atrial contraction phase 2. Isovolumetric contraction phase 3. Rapid ejection phase 4. Reduced ejection phase 5. Isovolumetric relaxation phase 6. Rapid filling phase 7. Reduced filling phase  ONE CARDIAC CYCLE QRS QRS complex complex Electro- cardiogram T (ECG) P P ATRIAL ATRIAL ATRIAL ATRIAL DIASTOLE DIASTOLE SYSTOLE SYSTOLE Phase VENTRICULAR VENTRICULAR VENTRICULAR DIASTOLE DIASTOLE SYSTOLE 120 3 Aortic valve closes Aortic valve opens 4 s of 90 Aorta Dicrotic notch 1 Atrial contraction phase. 2 Isovolumetric contraction phase. Pressure (mm Hg) 60 3 Rapid ejection phase. The Left 4 Reduced ejection phase. ventricle 2 5 5 Isovolumetric relaxation phase. 6 Rapid filling phase. Left AV 7 Reduced filling phase. 30 Left atrium Left AV valve closes valve opens Cardia 1 7 2 0 130 End-diastolic 2 volume volume (mL) 2 ventricular 1 c Left Stroke volume End-systolic volume 4 50 0 100 200 300 400 500 600 700 800 Time (msec) Phases of The Cardiac Cycle 1. Atrial systole: ̶ atrial contraction begins ̶ AV valves are still open since the end of previous cycle 2. Atria eject blood into ventricles: ̶ filling ventricles 3. Atrial systole ends: ̶ AV valves close ̶ ventricles contain maximum volume = end-diastolic volume (EDV) Phases of Cardiac Cycle 4. Ventricular systole (isovolumetric contraction): ̶ pressure in ventricles rises ̶ all heart valves are closed 5. Ventricular ejection: ̶ semilunar valves open ̶ blood flows into pulmonary trunk and aorta ̶ stroke volume (SV) = 60% of EDV 6. Ventricular pressure falls: ̶ semilunar valves close ̶ ventricles contain minimum volume = end-systolic volume (ESV), about 40% of EDV Phases of Cardiac Cycle 7. Ventricular diastole (isovolumetric relaxation): ̶ ventricular pressure is higher than atrial pressure ̶ all heart valves are closed 8. Atrial pressure becomes higher than ventricular pressure: ̶ AV valves open ̶ passive ventricular filling ̶ passive atrial emptying ̶ cardiac cycle ends Heart Sounds S : - loud sound 1 - closure of AV valves S : - loud sound 2 - closure of semilunar valves S : - soft sound 3 - blood flow into ventricles S : - soft sound 4 - atrial contraction - pathological sound Heart Murmurs Turbulent sounds produced by disturbance in blood flow through valves due to regurgitation or stenosis Energy of Heart Aerobic From mitochondrial breakdown of fatty acids and glucose Oxygen from circulating hemoglobin Cardiac muscles store oxygen in myoglobin Autonomic Innervation of the Heart Supplies atria & Supplies atria ventricles ONLY Autonomic Innervation of the Heart Sympathetic and parasympathetic nerve supply through cardiac plexuses Cardiac centers in medulla oblongata: ̶ cardioacceleratory center:  controls sympathetic neurons ( HR) ̶ cardioinhibitory center:  controls parasympathetic neurons ( HR) ̶ monitor cardiac reflexes:  baroreceptors (blood pressure)  chemoreceptors (arterial O and CO ) 2 2 NTS: solitary nucleus Autonomic Innervations of the Heart Sympathetic innervation: ̶ supply both atria and ventricles Parasympathetic innervation: ̶ through vagus nerves (X) ̶ supply atria ONLY ̶ ventricles have NO parasympathetic supply Autonomic tone: ̶ dual innervations maintains resting tone by releasing Ach and NE ̶ fine adjustments meet needs of other systems Cardiodynamics Cardiodynamics End-diastolic volume (EDV): = ±120 ml ̶ blood volume in ventricles at the end of diastole End-systolic volume (ESV): = ± 50 ml ̶ blood volume in ventricles at the end of systole Stroke volume (SV): ± 70 ml ̶ volume of blood ejected per beat ̶ = EDV — ESV Ejection fraction (Ef): 50% ̶ percentage of blood ejected from a ventricle each beat ̶ = SV / EDV X 100 Preload & Afterload Preload: ̶ventricular stretching during diastole ̶determined by venous return (VR):  blood flow back to the heart Afterload: ̶force produced by the ventricle to eject blood ̶determined by peripheral resistance (PR):  resistance of the arteries to blood flow Cardiac Output (CO) Blood volume ejected by a ventricle in 1minute Control of Cardiac Output Heart rate: adjusted by ANS or hormones Stroke volume: adjusted by changing EDV or ESV  Factors affecting Factors affecting heart rate (HR) stroke volume (SV) Skeletal Blood Changes in muscle volume peripheral activity circulation Atrial Venous Filling Autonomic innervation Hormones reflex return time Preload Contractility Vasodilation or vasoconstriction Autonomic End-diastolic End-systolic Hormones Afterload innervation volume volume HEART RATE (HR) STROKE VOLUME (SV) = EDV − ESV CARDIAC OUTPUT (CO) = HR × SV Factors Affecting Heart Rate & Stroke Volume Factors Control Heart Rate Autonomic nervous system: ̶  sympathetic  HR ̶  parasympathetic  HR Hormones: ̶ hormones  HR:  E, NE, and thyroid hormones  Venous return (VR): ̶  VR  HR Factors Control Stroke Volume EDV:  filling time  venous return  preload ESV: preload contractility afterload Bainbridge (Atrial) Reflex Increase in HR due to an increase in central venous pressure (CVP) Adjusts HR in response to venous return (VR) Mechanism: ̶  VR  right atrial pressure  stretch receptors in right atrium  sympathetic activity  HR Starling Law Within limits, the force of the cardiac muscle contraction is proportional to its initial length Mechanism: ̶ VR  EDV  cardiac muscle length  myocardial contractility  stroke volume Cardiac Reserve The difference between resting and maximal cardiac output Most healthy people can increase cardiac output by 300–500% Heart Failure Inability of the heart to pump sufficient quantities of blood to meet the requirements of the body tissues Lack of adequate blood flow to peripheral tissues and organs due to ventricular damage Summary Anatomy of the heart: ̶Chambers – layers – valves Systemic & pulmonary circulation Coronary circulation Conducting system – action potential – ECG Cardiac cycle Cardiodynamics