pap12e_lecture_ch20-modifiedd.ppt

CHAPTER 20: CVS: THE HEART 1 Anatomy of the Heart Located in the mediastinum – anatomical region extending from the sternum to the vertebral column, the first rib and between the lungs Apex at tip of left ventricle Base is broad posterior surface Anterior surfa...

CHAPTER 20: CVS: THE HEART 1 Anatomy of the Heart Located in the mediastinum – anatomical region extending from the sternum to the vertebral column, the first rib and between the lungs Apex at tip of left ventricle Base is broad posterior surface Anterior surface deep to sternum and ribs Right border faces right lung Left border (pulmonary border) faces left lung 2 3 Pericardium  Membrane surrounding and protecting the heart  Confines while still allowing free movement  2 main parts Fibrous pericardium – tough, dense irregular connective tissue – prevents overstretching, protection. Serous pericardium – thinner, more delicate membrane – double layer (parietal layer fused to fibrous pericardium, visceral layer also called epicardium) Pericardial fluid reduces friction – secreted into pericardial cavity 4 Pericardium and Heart Wall 5 Layers of the Heart Wall 1. Epicardium (external layer)  Visceral layer of serous pericardium  Smooth, slippery texture to outermost surface. Mesothelium and C.T. (Meso- =Middle) 2. Myocardium  95% of heart is cardiac muscle 3. Endocardium (inner layer)  Smooth lining for chambers of heart, valves and continuous with lining of large blood vessels, Endothelium and C.T. 6 Chambers of the Heart  2 atria – receiving chambers (upper chambers) Auricles increase capacity of atria  2 ventricles – pumping chambers (lower chambers)  Sulci – grooves with blood vessels and fat Coronary sulcus Anterior interventricular sulcus Posterior interventricular sulcus 7 Structure of the Heart 8 9 Right Atrium  Receives blood from Superior vena cava Inferior vena cava  Interatrial septum has fossa ovalis Remnant of foramen ovale in the fetal heart  Blood passes through tricuspid valve (right atrioventricular valve) into right ventricle 10 Right Ventricle  Forms anterior surface of heart  Trabeculae carneae (meaty ridges) – ridges formed by raised bundles of cardiac muscle fiber Part of conduction system of the heart  Tricuspid valve connected to chordae tendinae connected to papillary muscles  Interventricular septum divides the two ventricles  Blood leaves through pulmonary valve (pulmonary semilunar valve) into pulmonary trunk and then right and left pulmonary arteries 11 Internal Anatomy of the Heart 12 Left Atrium  About the same thickness as right atrium  Receives blood from the lungs through pulmonary veins  Passes through bicuspid/ mitral/ left atrioventricular valve into left ventricle 13 Left Ventricle  Thickest chamber of the heart  Forms apex  Chordae tendinae attached to papillary muscles  Blood passes through aortic valve (aortic semilunar valve) into ascending aorta  During fetal life ductus arteriosus shunts blood from pulmonary trunk to aorta (lung bypass) closes after birth with remnant called ligamentum arteriosum 14 Myocardial thickness  Thin-walled atria deliver blood under less pressure to ventricles  Right ventricle pumps blood to lungs Shorter distance, lower pressure, less resistance  Left ventricle pumps blood to body Longer distance, higher pressure, more resistance  Left ventricle works harder to maintain same rate of blood flow as right ventricle 15 Heart Valves and Circulation of Blood valves Atrioventricular  Tricuspid and bicuspid valves  Atria contracts/ ventricle relaxed AV valve opens, cusps project into ventricle In ventricle, papillary muscles are relaxed and chordae tendinae slack (not used-lacks usual firmness)  Atria relaxed/ ventricle contracts Pressure drives cusps upward until edges meet and close opening Papillary muscles contract tightening chordae tendinae presentation 16 17 Semilunar valves  Aortic and pulmonary valves  Valves open when pressure in ventricle exceeds pressure in arteries  As ventricles relax, some backflow permitted but blood fills valve cusps closing them tightly No valves guarding entrance to atria  As atria contracts, compresses and closes opening 18 19 Systemic and pulmonary circulation - 2 circuits in series  Systemic circulation Left side of heart Receives blood from lungs Ejects blood into aorta Systemic arteries, arterioles Systemic venules and veins lead back to right atrium  Pulmonary circulation Right side of heart Receives blood from systemic circulation Ejects blood into pulmonary trunk then pulmonary arteries Pulmonary veins takes blood to left atrium 20 21 Coronary circulation  Myocardium has its own network of blood vessels  Coronary arteries branch from ascending aorta Anastomoses provide alternate routes or collateral circuits Allows heart muscle to receive sufficient oxygen even if an artery is partially blocked  Coronary veins Collects in coronary sinus Empties into right atrium 22 Cardiac Muscle Tissue and the Cardiac Conduction System Histology  Shorter and less circular than skeletal muscle fibers  Branching gives “stair-step” appearance  Ends of fibers connected by intercalated discs  Discs contain desmosomes (hold fibers together) and gap junctions (allow action potential conduction from one fiber to the next)  Mitochondria are larger and more numerous than skeletal muscle  Same arrangement of actin and myosin  Requires Ca+ from extracellular fluid for contraction (20%), to trigger more Ca+ (80%) from sarcoplasmic reticulum. 23 24 Autorhythmic Fibers  Specialized cardiac muscle fibers  Self-excitable  Repeatedly generate action potentials that trigger heart contractions  2 important functions 1. Act as pacemaker 2. Form conduction system 25 Conduction system 1. Begins in sinoatrial (SA) node in right atrial wall Propagates through atria via gap junctions Atria contact 2. Reaches atrioventricular (AV) node in interatrial septum 3. Enters atrioventricular (AV) bundle (Bundle of His) Only site where action potentials can conduct from atria to ventricles 4. Enters right and left bundle branches which extends through interventricular septum toward apex 5. Finally, large diameter Purkinje fibers conduct action potential to remainder of ventricular myocardium Ventricles contract 26 27 Action Potentials and Contraction  Action potential initiated by SA node spreads out to excite “working” fibers called contractile fibers 1. Depolarization (Systole or Contraction) 2. Plateau 3. Repolarization (Diastole or Relaxation) 28 Action Potentials and Contraction 1. Depolarization – contractile fibers have stable resting membrane potential Voltage-gated fast Na+ channels open – Na+ flows in Then deactivate and Na+ inflow decreases 2. Plateau – period of maintained depolarization Due in part to opening of voltage-gated slow Ca2+ channels – Ca2+ moves from interstitial fluid into cytosol Ultimately triggers contraction Depolarization sustained due to voltage-gated K+ channels balancing Ca2+ inflow with K+ outflow 29 Action Potentials and Contraction 3. Repolarization – recovery of resting membrane potential  Resembles that in other excitable cells  Additional voltage-gated K+ channels open  Outflow K+ of restores negative resting membrane potential 30 Electrocardiogram  ECG or EKG  Composite record of action potentials produced by all the heart muscle fibers  Compare tracings from different leads with one another and with normal records  3 recognizable waves P, QRS, and T 31 Correlation of ECG Waves and Systole – contraction/ diastole – relaxation Systole  Cardiac action potential arises in SA node 1. P wave represents 2. Atrial contraction/ atrial systole 3. Action potential enters AV bundle and out over ventricles QRS complex Masks atrial repolarization 4. Contraction of ventricles/ ventricular systole Forms the QRS complex and continues during S-T segment 5. Repolarization of ventricular fibers T wave 6. Represents ventricular relaxation/ diastole 7. Arrhythmia: irregularity in heart rhythm- Heart Block 32  1 Depolarization of atrial contractile fibers produces P wave 6 6 Ventricular diastole (relaxation) P Action potential in SA node 0 0.2 2 Atrial systole (contraction) Seconds P P 0 0.2 0.4 0.6 0.8 Seconds 5 Repolarization 5 of ventricular contractile 0 0.2 fibers produces T Seconds wave 3 Depolarization of ventricular contractile fibers produces QRS complex T P R 4 Ventricular P 0 0.2 0.4 0.6 systole Seconds (contraction) Q S 0 0.2 0.4 Seconds P 0 0.2 0.4 33 Seconds Cardiac Cycle All events associated with one heartbeat Systole and diastole of atria and ventricles In each cycle, atria and ventricles alternately contract and relax  During atrial systole, ventricles are relaxed  During ventricle systole, atria are relaxed  Three phases: Relaxation of ventricular muscles, Ventricular filling and ventricular systole During relaxation period, both atria and ventricles are relaxed  The faster the heart beats, the shorter the relaxation period 34 Heart Sounds Sound of heartbeat comes primarily from blood turbulence caused by closing of heart valves 4 heart sounds in each cardiac cycle – only 2 loud enough to be heard  Lubb – AV valves close  Dupp – SL valves close 35 Cardiac Output CO = volume of blood ejected from left (and right) ventricle into aorta (and pulmonary trunk) each minute CO = stroke volume (SV) x heart rate (HR) Entire blood volume flows through pulmonary and systemic circuits each minute Cardiac reserve – difference between maximum CO and CO at rest  Average cardiac reserve 4-5 times resting value 36 Regulation of stroke volume  3 factors ensure left and right ventricles pump equal volumes of blood 1. Preload 2. Contractility 3. Afterload 37 Preload  Degree of stretch on the heart before it contracts  Greater preload increases the force of contraction  Frank-Starling law of the heart – the more the heart fills with blood during diastole, the greater the force of contraction during systole 38 Contractility  Strength of contraction at any given preload  Positive inotropic agents increase contractility Often promote Ca2+ inflow during cardiac action potential Increases stroke volume Epinephrine, norepinephrine  Negative inotropic agents decrease contractility acidosis, some anesthetics, and increased K+ and H+ in interstitial fluid 39 Afterload  Pressure that must be overcome before a semilunar valve can open  Increase in afterload causes stroke volume to decrease Blood remains in ventricle at the end of systole - The pressure in the ventricles must be greater than the systemic and pulmonary pressure to open the aortic and pulmonary valves, respectively. 40 Regulation of Heart Beat  Cardiac output depends on heart rate and stroke volume  Adjustments in heart rate important in short-term control of cardiac output and blood pressure  Autonomic nervous system and epinephrine/ norepinephrine most important(cardiovascular center in medulla oblongata gets inputs from baroreceptors and chemoreceptors > sympathetic and parasympathetic resoponse)  Sympathetic response increases HR, and parasympathetic response decreases HR 41 Chemical regulation of heart rate  Hormones Epinephrine and norepinephrine increase heart rate and contractility Thyroid hormones also increase heart rate and contractility  Cations Ionic imbalance can compromise pumping effectiveness Relative concentration of K+, Ca2+ and Na+ important Age (infant=140-160 beat/min), temperature, gender ( male 64-72 female 72-80) and physical fitness (more fitness lower heart rate) 42