Chapter 20 The Heart PDF - JA

Chapter 20 The Heart JA- PDF  Base of heart 2 1 1 Ribs 2 2 3 3...

Chapter 20 The Heart JA- PDF  Base of heart 2 1 1 Ribs 2 2 3 3 4 4 5 5 6 6 7 7 Apex of heart 8 8 9 9 10 10 Heart position relative to the rib cage. § The blood vessels in the cardiovascular system are subdivided into three circuits coronary, pulmonary, and systemic circuits § Coronary circuit ´It is the component of systemic circulation. ´Responsible for the drainage of blood to and from the cardiac musculature § Pulmonary circuit ´Carries blood to and from lungs § Systemic circuit ´Carries blood to and from the rest of the body § Each circuit begins and ends at the heart ´Blood travels through these circuits in sequence 3 § Types of blood vessels ´Arteries Carry blood away from heart ´Veins Return blood to heart ´Capillaries (exchange vessels) Interconnect smallest arteries and smallest veins Exchange dissolved gases, nutrients, and wastes between blood and surrounding tissues 4 § Four chambers of the heart ´Right atrium Receives blood from systemic circuit ´Right ventricle Pumps blood into pulmonary circuit ´Left atrium Receives blood from pulmonary circuit ´Left ventricle Pumps blood into systemic circuit 5 § Heart ´Great vessels connect at base (superior) ´Pointed tip is apex (inferior) ´Sits between two pleural cavities in mediastinum 6 § Pericardium ´Surrounds heart ´Outer fibrous pericardium ´Inner serous pericardium Outer parietal layer Inner visceral layer (epicardium) ´Pericardial cavity Between parietal and visceral layers Contains pericardial fluid 7 § Pericarditis ´Caused by pathogens in pericardium ´Inflamed pericardial surfaces rub against each other Producing distinctive scratching sound ´May cause cardiac tamponade Restricted movement of the heart Due to excess fluid in pericardial cavity 8 § Superficial anatomy of the heart ´Two thin-walled atria Each with an expandable outer auricle ´Sulci (grooves) Contain fat and blood vessels Coronary sulcus ´Marks border between atria and ventricles Anterior interventricular sulcus and posterior interventricular sulcus ´Mark boundary between left and right ventricles 9  Left subclavian artery Left common carotid artery 10 Ligamentum Brachiocephalic trunk arteriosum Left pulmonary Ascending artery aorta Pulmonary Superior trunk vena cava Auricle of left atrium Auricle of Left coronary artery right atrium (LCA) Right atrium Anterior interventricular Right Right sulcus coronary ventricle artery Left ventricle Coronary sulcus Anterior interventricular Marginal branch branch of LCA of right coronary artery Anterior surface of the heart, cadaver dissection.  Arch of aorta Left pulmonary artery Right pulmonary 11 Left pulmonary veins artery Fat and vessels Superior in coronary vena cava Left sulcus atrium Coronary Right sinus pulmonary veins Right (superior Left atrium and inferior) ventricle Right Inferior ventricle vena cava Fat and vessels in posterior interventricular sulcus Major anatomical features on the posterior surface. Coronary arteries (which supply the heart itself) are shown in red; coronary veins are shown in blue. § Heart wall consists of three distinct layers ´ Visceral layer of serous pericardium (epicardium) Covers surface of heart Covered by parietal layer of serous pericardium ´ Myocardium Cardiac muscle tissue ´ Endocardium Covers inner surfaces of heart Simple squamous epithelium and areolar tissue 12 § Internal anatomy § Chambers of heart are separated by muscular partitions (septa) ´Interatrial septum Separates atria ´Interventricular septum Separates ventricles Much thicker than interatrial septum 13 § Atrioventricular (AV) valves ´ Tricuspid (right side ) and mitral/Bicuspid valves ( left side) ´ Folds of fibrous tissue that extend into openings between atria and ventricles ´ Permit blood flow in one direction From right atrium to right ventricle From left atrium to left ventricle § Semilunar valves ´ Pulmonary and aortic valves ´ Prevent backflow of blood into ventricles T&R 14 § Right atrium receives blood from ´Superior vena cava Carries blood from head, neck, upper limbs, and chest ´Inferior vena cava Carries blood from trunk, viscera, and lower limbs Tue15 § Right atrium ´Foramen ovale Before birth, is an opening through interatrial septum Connects the two atria of fetal heart Closes at birth, eventually forming fossa ovalis 16 ´Pectinate muscles Prominent muscular ridges On anterior atrial wall and inner surface of auricle PA & TV § Blood flows from right atrium to right ventricle ´Tricuspid valve (right atrioventricular valve) Has three cusps Prevents backflow of blood ´Free edges of valve attach to chordae tendineae from papillary muscles of ventricle Prevent valve from opening backward 18  Left common carotid artery Left subclavian artery 19 Brachiocephalic trunk Ligamentum arteriosum Aortic arch Pulmonary trunk Superior vena cava Pulmonary valve Right pulmonary Left pulmonary arteries arteries Ascending aorta Left pulmonary veins Fossa ovalis Left atrium Opening of coronary sinus Interatrial septum Aortic valve Right atrium Cusp of mitral valve Pectinate muscles Chordae tendineae Conus arteriosus Left ventricle Cusp of tricuspid valve Interventricular septum Papillary muscle Trabeculae carneae Right ventricle Inferior vena cava Moderator band Descending aorta A diagrammatic frontal section through the heart, showing anatomical features and the path of blood flow (marked by arrows) through the atria, ventricles, and associated vessels. § Right ventricle ´Trabeculae carneae Muscular ridges on internal surface (of both ventricles) ´Moderator band Muscular ridge that delivers stimulus for contraction to papillary muscles 20 21 Chordae tendineae Papillary muscles Papillary muscles and chordae tendineae support the mitral valve and tricuspid valve.  Left subclavian artery 22 Left common carotid artery Brachiocephalic trunk Superior vena cava Ascending aorta Pulmonary trunk Cusp of pulmonary valve Auricle of left atrium Right atrium Cusp of mitral valve Chordae tendineae Cusp of Papillary muscles tricuspid valve Right ventricle Left ventricle Trabeculae carneae Interventricular Anterior view of a frontally septum sectioned heart showing internal features and valves. § Conus arteriosus ´At superior end of right ventricle ´Ends at pulmonary valve Three semilunar cusps Leads to pulmonary trunk ´Start of pulmonary circuit ´Divides into left and right pulmonary arteries 23 § Left atrium ´ Receives blood from left and right pulmonary veins ´ Blood passes to left ventricle through mitral valve (left atrioventricular valve or bicuspid valve) Two cusps § Left ventricle ´ Similar to right ventricle but does not have moderator band ´ Blood leaves left ventricle through aortic valve into ascending aorta ´ Aortic sinuses Saclike expansions at base of ascending aorta ´ Ascending aorta turns to become aortic arch Becomes descending aorta 24 § Compared to left ventricle, the right ventricle ´Holds and pumps the same amount of blood ´Has thinner walls ´Develops less pressure ´Is more pouch-shaped than round 25  Left common carotid artery Left subclavian artery 26 Brachiocephalic trunk Ligamentum arteriosum Aortic arch Pulmonary trunk Superior vena cava Pulmonary valve Right pulmonary Left pulmonary arteries arteries Ascending aorta Left pulmonary veins Fossa ovalis Left atrium Opening of coronary sinus Interatrial septum Aortic valve Right atrium Cusp of mitral valve Pectinate muscles Chordae tendineae Conus arteriosus Left ventricle Cusp of tricuspid valve Interventricular septum Papillary muscle Trabeculae carneae Right ventricle Inferior vena cava Moderator band Descending aorta a A diagrammatic frontal section through the heart, showing anatomical features and the path of blood flow (marked by arrows) through the atria, ventricles, and associated vessels. § Heart valves ´ Prevent backflow of blood § Atrioventricular (AV) valves ´ Between atria and ventricles ´ When ventricles contract, Blood pressure closes valves Papillary muscles contract and tense chordae tendineae ´Prevents regurgitation (backflow) of blood into atria § Semilunar valves ´ Pulmonary and aortic valves ´ Prevent backflow of blood into ventricles ´ No muscular braces ´ Valvular heart disease (VHD) Deterioration of valve function May develop after carditis (inflammation of heart) ´May result from rheumatic fever (inflammatory autoimmune response to streptococcal bacteria) 27  Tricuspid valve Cardiac Mitral valve (closed) skeleton (closed) 28 Right Left ventricle ventricle Contracting ventricles Aortic valve (open) Pulmonary valve (open) b When the ventricles are contracting, the tricuspid and mitral valves are closed and the aortic and pulmonary valves are open. In the frontal section, note the attachment of the mitral valve to the Aortic valve open chordae tendineae and papillary muscles. 29 Aorta Left atrium Aortic sinus Mitral valve Contracting ventricles (closed) Aortic valve (open) Chordae tendineae (tense) Papillary muscles (contracted) Left ventricle (contracted) b When the ventricles are contracting, the tricuspid and mitral valves are closed and the aortic and pulmonary valves are open. In the frontal section, note the attachment of the mitral valve to the chordae tendineae and papillary muscles. § Coronary circulation ´Supplies blood to muscle tissue of heart ´Coronary arteries Originate at aortic sinuses Elevated blood pressure and elastic rebound of aorta maintain blood flow through coronary arteries § Right coronary artery ´Supplies blood to Right atrium Portions of both ventricles Portions of electrical conducting system of heart ´Gives rise to Marginal arteries Posterior interventricular artery 30 § Left coronary artery ´Supplies blood to Left ventricle Left atrium Interventricular septum ´Gives rise to Circumflex artery Anterior interventricular artery § Arterial anastomoses ´Interconnect anterior and posterior interventricular arteries ´Maintain constant blood supply to cardiac muscle 31 § Cardiac veins ´Great cardiac vein Drains blood from region supplied by anterior interventricular artery Returns blood to coronary sinus ´Opens into right atrium ´Posterior vein of left ventricle, middle cardiac vein, and small cardiac vein Empty into great cardiac vein or coronary sinus ´Anterior cardiac veins empty into right atrium 32  Left pulmonary Left pulmonary Auricle of veins artery left atrium Right 33 Circumflex pulmonary artery artery Great cardiac Superior vein vena cava Marginal artery Right pulmonary Posterior vein veins of left ventricle Left atrium Right atrium Inferior vena cava Coronary sinus Middle cardiac vein Right ventricle Posterior interventricular artery c A posterior view of the heart; the vessels have been injected with colored latex (liquid rubber). § Coronary artery disease (CAD) ´Areas of partial or complete blockage of coronary circulation § Cardiac muscle cells need a constant supply of oxygen and nutrients ´Reduction in blood flow to heart muscle reduces cardiac performance § Coronary ischemia ´Reduced circulatory supply from partial or complete blockage of coronary arteries 34 § Coronary artery disease (CAD) ´Usual cause is formation of a fatty deposit, or atherosclerotic plaque, in wall of coronary vessel ´The plaque, or an associated thrombus (clot), narrows passageway and reduces blood flow ´Spasms in smooth muscles of vessel wall can further decrease or stop blood flow 35 § Angina pectoris ´Commonly one of the first symptoms of CAD ´A temporary ischemia develops when workload of heart increases ´Individual may feel comfortable at rest ´Exertion or emotional stress can produce sensations of pressure, chest constriction, and pain ´Pain may radiate from sternal area to arms, back, and neck 36 § Myocardial infarction (MI), or heart attack ´Part of coronary circulation becomes blocked ´Cardiac muscle cells die from lack of oxygen ´Death of affected tissue creates a nonfunctional area known as an infarct ´Most commonly results from severe CAD ´Coronary thrombosis Thrombus formation at a plaque Most common cause of an MI 37 § Treatment of CAD ( coronary artery disease ) and myocardial infarction ´About 25 percent of MI patients die before obtaining medical assistance 65 percent of MI deaths among people under age 50 occur within an hour § Risk factor modification ´Stop smoking ´Treat high blood pressure ´Adjust diet to lower cholesterol and promote weight loss ´Reduce stress ´Increase physical activity 38 § Drug treatments are used to ´ Reduce coagulation (e.g., aspirin and coumadin) ´ Block sympathetic stimulation (propranolol or metoprolol) ´ Cause vasodilation (e.g., nitroglycerin) ´ Block calcium ion movement into muscle cells (calcium ion channel blockers) ´ Relieve pain and help dissolve clots (in MI) § Noninvasive surgery ´ Atherectomy Long, slender catheter is inserted into coronary artery to remove plaque ´ Balloon angioplasty Tip of catheter contains inflatable balloon Inflated balloon presses plaque against vessel walls Plaques commonly redevelop A stent may be inserted to hold vessel open 39 § Coronary artery bypass graft (CABG) ´Small section of another vessel is removed Used to create detour around obstructed portion of coronary artery ´Up to four coronary arteries can be rerouted during a single operation Single, double, triple, or quadruple coronary bypasses 40 § Heartbeat ´A single cardiac contraction ´All heart chambers contract in series First the atria Then the ventricles § Two types of cardiac muscle cells ´ a. Autorhythmic cells ´ they are pacemaker & conducting cells of the conducting system ´ Control and coordinate heartbeat ´ b. Contractile cells Produce contractions that propel blood summer § Conducting system ´Consists of specialized cardiac muscle cells Initiate and distribute electrical impulses that stimulate contraction ´Autorhythmicity Cardiac muscle tissue contracts without neural or hormonal stimulation ´Pacemaker cells found in Sinoatrial (SA) node—in wall of right atrium Atrioventricular (AV) node—at junction between atria and ventricles ´Conducting cells found in Internodal pathways of atria Atrioventricular (AV) bundle( Bundle of His ), bundle branches, and Purkinje fibers of ventricles 42 § Pacemaker potential ´Gradual depolarization of pacemaker cells Do not have a stable resting membrane potential § SA node depolarizes first ´Establishing sinus rhythm/ basic heart rhythm § Parasympathetic stimulation slows heart rate 43 § Impulse conduction through the heart 1. SA node activity and atrial activation begin 2. Stimulus spreads across atria and reaches AV node 3. Impulse is delayed for 100 msec at AV node Atrial contraction begins 44 45 1 SA node activity and ECG Tracing atrial activation begin SA node (60–100 action potentials per minute at rest). Time = 0 46 2 Stimulus spreads across the P wave: atrial atrial surfaces and reaches depolarization the AV node. AV node P Elapsed time = 50 msec 47 3 There is a 100-msec delay P–R interval: at the AV node. Atrial conduction through contraction begins. AV node and AV bundle AV bundle Bundle P branches Elapsed time = 150 msec § Impulse conduction through the heart 4. Impulse travels in AV bundle to left and right bundle branches in interventricular septum To Purkinje fibers And to papillary muscles via moderator band 5. Purkinje fibers distribute impulse to ventricular myocardium Atrial contraction is completed Ventricular contraction begins 48 49 4 The impulse travels along the Q wave: interventricular septum within beginning of ventricular depolarization the AV bundle and the bundle branches to the Purkinje fibers and, by the moderator band, to the papillary muscles of the right ventricle. P Moderator band Q Elapsed time = 175 msec 50 QRS complex: 5 The impulse is distributed by completion of ventricular Purkinje fibers and relayed depolarization throughout the ventricular R myocardium. Atrial contraction is completed, and ventricular contraction begins. P Elapsed time = 225 msec Purkinje fibers QS § Disturbances in heart rhythm ´Bradycardia—abnormally slow heart rate ´Tachycardia—abnormally fast heart rate ´Ectopic pacemaker Abnormal cells generate high rate of action potentials Bypasses conducting system Disrupts timing of ventricular contractions § Electrocardiogram (ECG or EKG) ´A recording of electrical events in the heart ´Obtained by placing electrodes at specific locations on body surface ´Abnormal patterns are used to diagnose damage 51 53 a Electrode placement for recording a standard ECG.  800 msec 54 R R +1 P wave (atria T wave S–T depolarize) (ventricles repolarize) P–R segment segment +0.5 0 Millivolts Q S S–T P–R interval interval –0.5 Q–T QRS complex interval (ventricles depolarize) 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Time (sec) An ECG printout is a strip of graph paper containing a record of the electrical events monitored by the electrodes. The placement of electrodes on the body surface affects the size and shape of the waves recorded. The example is a normal ECG; the enlarged section indicates the major components of the ECG and the measurements most often taken during clinical analysis. § Cardiac contractile cells ´Form bulk of atrial and ventricular walls ´Receive stimulus from Purkinje fibers ´ Resting membrane potential Of ventricular cell is about –90 mV Of atrial cell is about –80 mV § Intercalated discs ´Interconnect cardiac contractile cells ´Membranes of adjacent cells are Held together by desmosomes Linked by gap junctions ´Transfer force of contraction from cell to cell ´Propagate action potentials 55 56 Intercalated discs Cardiac muscle tissue LM × 575 c Cardiac muscle tissue § Characteristics of cardiac contractile cells ´Small size ´Single, central nucleus ´Branching interconnections between cells ´Intercalated discs § Action potential in cardiac contractile cells 1. Rapid depolarization Massive influx of Na+ through fast sodium channels 2. Plateau Extracellular Ca2+ enters cytosol through slow calcium channels 3. Repolarization K+ rushes out of cell through slow potassium channels 57  1 Rapid Depolarization 2 The Plateau 3 Repolarization 58 Cause: Na+ entry Cause: Ca2+ entry Cause: K+ loss Duration: 3–5 msec Duration: ~175 msec Duration: 75 msec Ends with: Closure of Ends with: Closure Ends with: Closure voltage-gated fast of slow calcium of slow potassium sodium channels channels channels +30 2 0 1 mV Relative 3 refractory Absolute refractory period KEY –90 period Absolute refractory period 0 100 200 300 Relative refractory Stimulus Time (msec) period a Events in an action potential in a ventricular contractile cell. § Role of calcium ions in cardiac contractions 1. Extracellular Ca2+ crosses plasma membrane during plateau phase Provides roughly 20 percent of Ca2+ required for contraction 2. Entry of extracellular Ca2+ triggers release of additional Ca2+ from sarcoplasmic reticulum (SR) ´Cardiac muscle tissue Very sensitive to extracellular Ca2+ concentrations ´As slow calcium channels close, Intracellular Ca2+ is pumped back into SR or out of cell 59 § Energy for cardiac contractions ´Aerobic energy From mitochondrial breakdown of fatty acids and glucose Oxygen is delivered by circulation Cardiac contractile cells store oxygen in myoglobin The Cardiac Cycle § Cardiac cycle ´From start of one heartbeat to beginning of next ´Includes alternating periods of contraction and relaxation § Phases of the cardiac cycle within each chamber ´Systole (contraction) ´Diastole (relaxation) 61 SmartArt Video: The Cardiac Cycle 62 § Heart sounds ´Detected with a stethoscope ´S1—Loud sound as AV valves close ´S2—Loud sound as semilunar valves close ´S3, S4—Soft sounds Blood flowing into ventricles and atrial contraction ´Heart murmur Sounds produced by regurgitation through valves Placements of a stethoscope for listening to the different sounds produced by individual valves 63 § Cardiac output (CO) ´ Volume pumped by left ventricle in one minute ´ CO = HR × SV CO = cardiac output (mL/min) HR = heart rate (beats/min) SV = stroke volume (mL/beat) Stroke volume: The amount of blood pumped by the left ventricle of the heart in one contraction. § Normal Output § It’s different for different people, depending on their size. Usually, an adult heart pumps about 5 liters of blood per minute at rest. But when you run or exercise, your heart may pump 3-4 times that much to make sure your body gets enough oxygen and fuel. 64 § Stroke volume (SV) ´SV = EDV – ESV ´End-diastolic volume (EDV) Amount of blood in each ventricle at end of ventricular diastole ´End-systolic volume (ESV) Amount of blood remaining in each ventricle at end of ventricular systole ´Ejection fraction Percentage of EDV ejected during contraction 65 § Factors affecting heart rate ´Autonomic activity ´Circulating hormones § Autonomic innervation ´Cardiac plexus innervates heart ´Vagus nerves (CN X) carry parasympathetic fibers to small ganglia in cardiac plexus ´Cardiac centers of medulla oblongata Cardioacceleratory center controls sympathetic neurons that increase heart rate Cardioinhibitory center controls parasympathetic neurons that slow heart rate 66 § Cardiac reflexes ´Cardiac centers Monitor blood pressure (baroreceptors) Monitor arterial oxygen and carbon dioxide levels (chemoreceptors) Adjust cardiac activity § Autonomic tone ´Maintained by dual innervation and release of ACh and NE 67  Vagal nucleus Cardioinhibitory center 68 Cardioacceleratory center Medulla oblongata Vagus nerve (X) Autonomic Innervation of the Spinal cord Heart. Sympathetic Parasympathetic Parasympathetic preganglionic Sympathetic fiber preganglionic Synapses in fiber cardiac plexus Sympathetic ganglia Parasympathetic (cervical ganglia and postganglionic superior thoracic fibers ganglia [T1–T4]) Sympathetic postganglionic fiber Cardiac nerve § Effects on pacemaker cells of SA node ´ACh released by parasympathetic neurons Decreases heart rate ´NE released by sympathetic neurons Increases heart rate 69 § Bainbridge reflex (atrial reflex) ´Adjustments in heart rate in response to increase in venous return Amount of blood returning to heart through veins ´Stretch receptors in right atrium Trigger increase in heart rate by stimulating sympathetic activity § Hormonal effects on heart rate ´Heart rate is increased by Epinephrine (E) Norepinephrine (NE) Thyroid hormone (T3) 71 § Factors affecting stroke volume ´Changes in EDV or ESV affect stroke volume And thus cardiac output ´Two factors affect EDV Filling time ´Duration of ventricular diastole Venous return § Preload ´Degree of ventricular stretching during ventricular diastole ´Directly proportional to EDV ´Affects ability of muscle cells to produce tension 72 § Three factors affect ESV ´Preload Ventricular stretching during diastole ´Contractility Force produced during contraction at a given preload Affected by autonomic activity and hormones ´Afterload Tension that must be produced by ventricle to open semilunar valve and eject blood 73 § Effects of autonomic activity on contractility ´Sympathetic stimulation NE released by cardiac nerves E and NE released by adrenal medullae Causes ventricles to contract with more force Increases ejection fraction, decreases ESV ´Parasympathetic stimulation ACh released by vagus nerves Reduces force of cardiac contractions 74 § Summary: the control of cardiac output ´Heart rate control factors Autonomic nervous system ´Sympathetic and parasympathetic Circulating hormones Venous return and stretch receptors ´Stroke volume control factors EDV—filling time and rate of venous return ESV—preload, contractility, and afterload 75  Maximum for trained athletes 40 exercising at Factors affecting Factors affecting heart rate (HR) peak levels 76 stroke volume (SV) 35 Skeletal Blood Changes in muscle volume peripheral activity circulation 30 Bainbridge Venous Filling Autonomic (atrial) Hormones return time innervation reflex Cardiac output (L/min) Normal range 25 of cardiac output during Vasodilation heavy exercise Preload Contractility or vasoconstriction 20 Autonomic End-diastolic End-systolic Hormones Afterload innervation volume volume 15 10 HEART RATE (HR) STROKE VOLUME (SV) = EDV – ESV Average resting cardiac output 5 Heart failure CARDIAC OUTPUT (CO) = HR x SV 0 a Cardiac output varies widely b Factors affecting cardiac output to meet metabolic demands § Cardiac reserve ´Difference between resting and maximal cardiac outputs § Heart and vessels of cardiovascular system ´Cardiovascular regulation Ensures adequate circulation to body tissues ´Cardiac centers Control heart rate and peripheral blood vessels ´Cardiovascular system responds to Changing activity patterns Circulatory emergencies 77