BIO2870 Chapter 20 Slides and Lecture Notes
BIO2870 Chapter 20 Slides and Lecture Notes Bio 2870
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This 56 page Class Notes was uploaded by Makenna McClellan on Sunday August 7, 2016. The Class Notes belongs to Bio 2870 at Wayne State University taught by Dr. Jyoti Nautiyal in Fall 2016. Since its upload, it has received 11 views. For similar materials see Anatomy & Physiology in Science at Wayne State University.
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Ch-20 The Heart Nov-17-2015 Bio-2870 Anatomy and Physiology Chapter 20 Heart 1 Ch-20 The Heart Nov-17-2015 Introduction to Cardiovascular System • The Pulmonary Circuit – Carries blood to and from gas exchange surfaces of lungs • The Systemic Circuit – Carries blood to and from the body • Blood alternates between pulmonary circuit and systemic circuit ▯ Three Types of Blood Vessels 1) Arteries : Carry blood away from heart 2) Veins : Carry blood to heart 3) Capillaries : Networks between arteries and veins ▯ Also called exchange vessels ▯ Exchange materials between blood and tissues ▯ Materials include dissolved gases, nutrients, wastes 2 Ch-20 The Heart Nov-17-2015 Introduction to Cardiovascular System Figure 20–1 An Overview of the Cardiovascular System. 3 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart Four Chambers of the Heart ▯ 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 Figure 20–2a The Location of the Heart in tCavityracic 4 Ch-20 The Heart Nov-17-2015 1-9 Body Cavities Ch-20 The Heart Nov-17-2015 Anatomy of the Heart The Pericardium ▯ Double lining of the pericardial cavity ▯ Parietal pericardium ▯ Visceral pericardium ▯ Pericardial cavity ▯ Pericardial sac Figure 20–c2 The Location of the Heart in the Thoracic Cavi6y Ch-20 The Heart Nov-17-2015 Anatomy of the Heart The Heart Wall ▯ Epicardium (outer layer) ▯ Visceral pericardium ▯ Covers the heart ▯ Myocardium (middle layer) ▯ Muscular wall of the heart ▯ Concentric layers of cardiac muscle tissue ▯ Atrial myocardium wraps around great vessels ▯ Two divisions of ventricular myocardium ▯ Endocardium (inner layer) ▯ Simple squamous epithelium Figure 20–4 The Heart Wall 7 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart Cardiac Muscle Tissue ▯ Small size ▯ Single, central nucleus ▯ Branching interconnections between cells ▯ Intercalated discs Figure 20–5 Cardiac Muscle Cells 8 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart Intercalated discs ▯ Interconnect cardiac muscle cells ▯ Secured by desmosomes ▯ Linked by gap junctions ▯ Convey force of contraction ▯ Propagate action potentials Figure 20–5 Cardiac Muscle Cells 9 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart 10 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart • Internal Anatomy and Organization – Interatrial septum : separates atria – Interventricular septum : separates ventricles – Atrioventricular (AV) valves • Connect right atrium to right ventricle and left atrium to left ventricle • The fibrous flaps that form bicuspid (2) and tricuspid (3) valves • Permit blood flow in one direction: atria to ventricles 11 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart • The Right Atrium – Superior vena cava • Receives blood from head, neck, upper limbs, and chest – Inferior vena cava • Receives blood from trunk, viscera, and lower limbs – Coronary sinus • Cardiac veins return blood to coronary sinus • Coronary sinus opens into right atrium – Foramen ovale • Before birth, is an opening through interatrial septum • Connects the two atria • Seals off at birth, forming fossa ovalis – Pectinate muscles • Contain prominent muscular ridges • On anterior atrial wall and inner surfaces of right auricle 12 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart Figure 20–6a-b The Sectional Anatomy of the Heart 13 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart • The Right Ventricle – Free edges attach to chordae tendineae from papillary muscles of ventricle – Prevent valve from opening backward – Right atrioventricular (AV) Valve • Also called tricuspid valve • Opening from right atrium to right ventricle • Has three cusps • Prevents backflow – Trabeculae carneae • Muscular ridges on internal surface of right (and left) ventricle • Includes moderator band: – ridge contains part of conducting system – coordinates contractions of cardiac muscle cells 14 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart • The Pulmonary Circuit – Conus arteriosus (superior end of right ventricle) leads to pulmonary trunk – Pulmonary trunk divides into left and right pulmonary arteries – Blood flows from right ventricle to pulmonary trunk through pulmonary valve – Pulmonary valve has three semilunar cusps 15 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart • The Left Atrium – Blood gathers into left and right pulmonary veins – Pulmonary veins deliver to left atrium – Blood from left atrium passes to left ventricle through left atrioventricular (AV) valve – A two-cusped bicuspid valve or mitral valve • The Left Ventricle – Holds same volume as right ventricle – Is larger; muscle is thicker and more powerful – Similar internally to right ventricle but does not have moderator band – Systemic circulation • Blood leaves left ventricle through aortic valve into ascending aorta • Ascending aorta turns (aortic arch) and becomes descending aorta 16 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart • Structural Differences between the Left and Right Ventricles – Right ventricle wall is thinner, develops less pressure than left ventricle – Right ventricle is pouch-shaped, left ventricle is round Figure 20–7 Structural Differences between the Left and Right Ventricles 17 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart The Heart Valves ▯ Two pairs of one-way valves prevent backflow during contraction ▯ Atrioventricular (AV) valves ▯ Between atria and ventricles ▯ Blood pressure closes valve cusps during ventricular contraction ▯ Papillary muscles tense chordae tendineae: prevent valves from swinging into atria ▯ Semilunar valves ▯ Pulmonary and aortic tricuspid valves ▯ Prevent backflow from pulmonary trunk and aorta into ventricles ▯ Have no muscular support ▯ Three cusps support like tripod ▯ Aortic Sinuses ▯ At base of ascending aorta ▯ Sacs that prevent valve cusps from sticking to aorta ▯ Origin of right and left coronary arteries 18 Ch-20 The Heart Nov-17-2015 Anatomy of the Heart Figure 20–8 Valves of the Heart 19 Ch-20 The Heart Nov-17-2015 The Conducting System • Heartbeat – A single contraction of the heart – The entire heart contracts in series • First the atria • Then the ventricles • Two Types of Cardiac Muscle Cells – Conducting system : Controls and coordinates heartbeat – Contractile cells : Produce contractions that propel blood • A system of specialized cardiac muscle cells – Initiates and distributes electrical impulses that stimulate contraction • Automaticity – Cardiac muscle tissue contracts automatically 20 Ch-20 The Heart Nov-17-2015 The Conducting System ▯ The Cardiac Cycle ▯ Begins with action potential at SA node ▯ Transmitted through conducting system ▯ Produces action potentials in cardiac muscle cells (contractile cells) Electrocardiogram (ECG) ▯ Electrical events in the cardiac cycle can be recorded on an electrocardiogram (ECG) Figure 20–11 An Overview of Cardiac Physiology 21 Ch-20 The Heart Nov-17-2015 The Conducting System • Structures of the Conducting System – Sinoatrial (SA) node - wall of right atrium – Atrioventricular (AV) node - junction between atria and ventricles – Conducting cells - throughout myocardium • Conducting Cells – Interconnect SA and AV nodes – Distribute stimulus through myocardium – In the atrium • Internodal pathways – In the ventricles • AV bundle and the bundle branches • Prepotential – Also called pacemaker potential – Resting potential of conducting cells • Gradually depolarizes toward threshold – SA node depolarizes first, establishing heart rate 22 Ch-20 The Heart Nov-17-2015 The Conducting System Figure 20–12 The Conducting System of the Heart 23 Ch-20 The Heart Nov-17-2015 The Conducting System ▯ Heart Rate ▯ The Sinoatrial (SA) Node ▯ SA node generates ▯ In posterior wall of right atrium 80–100 action ▯ Contains pacemaker cells potentials per minute ▯ Connected to AV node by ▯ Parasympathetic internodal pathways stimulation slows ▯ Begins atrial activation (Step 1) heart rate ▯ AV node generates 40–60 action potentials per minute Figure 20–13 Impulse Conduction through the Heart 24 Ch-20 The Heart Nov-17-2015 The Conducting System ▯ The Atrioventricular (AV) Node ▯ In floor of right atrium ▯ Receives impulse from SA node (Step 2) ▯ Delays impulse (Step 3) ▯ Atrial contraction begins Figure 20–13 Impulse Conduction through the Heart 25 Ch-20 The Heart Nov-17-2015 The Conducting System ▯ The AV Bundle ▯ In the septum ▯ Carries impulse to left and right bundle branches ▯ Which conduct to Purkinje fibers (Step 4) ▯ And to the moderator band ▯ Which conducts to papillary muscles Figure 20–13 Impulse Conduction through the Heart 26 Ch-20 The Heart Nov-17-2015 The Conducting System ▯ Purkinje Fibers ▯ Distribute impulse through ventricles (Step 5) ▯ Atrial contraction is completed ▯ Ventricular contraction begins Figure 20–13 Impulse Conduction through the Heart 27 Ch-20 The Heart Nov-17-2015 The Conducting System • Abnormal Pacemaker Function – Bradycardia: abnormally slow heart rate – Tachycardia: abnormally fast heart rate – Ectopic pacemaker • Abnormal cells • Generate high rate of action potentials • Bypass conducting system • Disrupt ventricular contractions 28 Ch-20 The Heart Nov-17-2015 The Conducting System Electrocardiogram (ECG or EKG) – A recording of electrical events in the heart – Obtained by electrodes at specific body locations – Abnormal patterns diagnose damage Figure 20–14b An Electrocardiogram: An ECG Printout 29 Ch-20 The Heart Nov-17-2015 The Conducting System • Features of an ECG – P wave : Atria depolarize – QRS complex : Ventricles depolarize – T wave : Ventricles repolarize ▯ Time Intervals Between ECG Waves ▯ P–R interval ▯ From start of atrial depolarization ▯ To start of QRS complex ▯ Q–T interval ▯ From ventricular depolarization ▯ To ventricular repolarization Figure 20–14a An Electrocardiogram: Electrode Placement for Recording a Stand30d ECG Ch-20 The Heart Nov-17-2015 The Conducting System • Contractile Cells – Purkinje fibers distribute the stimulus to the contractile cells, which make up most of the muscle cells in the heart – Resting Potential • Of a ventricular cell: about –90 mV • Of an atrial cell: about –80 mV 31 Ch-20 The Heart Nov-17-2015 The Conducting System Figure 20–15 The Action Potential in Skeletal and Cardiac Muscle 32 Ch-20 The Heart Nov-17-2015 The Conducting System Figure 20–15 The Action Potential in Skeletal and Cardiac Muscle 33 Ch-20 The Heart Nov-17-2015 The Conducting System • Refractory Period – Absolute refractory period • Long • Cardiac muscle cells cannot respond – Relative refractory period • Short • Response depends on degree of stimulus • Timing of Refractory Periods – Length of cardiac action potential in ventricular cell • 250–300 msecs: – 30 times longer than skeletal muscle fiber – long refractory period prevents summation and tetany 34 Ch-20 The Heart Nov-17-2015 The Conducting System • The Role of Calcium Ions in Cardiac Contractions – Contraction of a cardiac muscle cell is produced by an increase in calcium ion concentration around myofibrils – 20% of calcium ions required for a contraction • Calcium ions enter plasma membrane during plateau phase – Arrival of extracellular Ca 2+ • Triggers release of calcium ion reserves from sarcoplasmic reticulum – As slow calcium channels close • Intracellular Ca 2+ is absorbed by the SR • Or pumped out of cell – Cardiac muscle tissue • Very sensitive to extracellular Ca 2+ concentrations 35 Ch-20 The Heart Nov-17-2015 The Conducting System • The Energy for Cardiac Contractions – Aerobic energy of heart • From mitochondrial breakdown of fatty acids and glucose • Oxygen from circulating hemoglobin • Cardiac muscles store oxygen in myoglobin 36 Ch-20 The Heart Nov-17-2015 The Cardiac Cycle • Cardiac cycle = The period between the start of one heartbeat and the beginning of the next • Includes both contraction and relaxation • Phases of the Cardiac Cycle – Within any one chamber • Systole (contraction) • Diastole (relaxation) • 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 37 Ch-20 The Heart Nov-17-2015 The Cardiac Cycle Figure 20–16 Phases of the Cardiac Cycle 38 Ch-20 The Heart Nov-17-2015 The Cardiac Cycle Figure 20–17 Pressure and Volume Relationships in the Cardiac Cycle Wiggers diagram is a standard diagram used in cardiac physiology named after Dr. Carl J. Wiggers. 39 Ch-20 The Heart Nov-17-2015 The Cardiac Cycle • Cardiac Cycle and Heart Rate – At 75 beats per minute • Cardiac cycle lasts about 800 msecs – When heart rate increases • All phases of cardiac cycle shorten, particularly diastole Eight Steps in the Cardiac Cycle 1. Atrial systole ▯ Atrial contraction begins ▯ Right and left AV valves are open 2. Atria eject blood into ventricles ▯ Filling ventricles 3. Atrial systole ends ▯ AV valves close ▯ Ventricles contain maximum blood volume ▯ Known as end-diastolic volume (EDV) 40 Ch-20 The Heart Nov-17-2015 The Cardiac Cycle Eight Steps in the Cardiac Cycle 4. Ventricular systole • Isovolumetric ventricular contraction • Pressure in ventricles rises • AV valves shut 5. Ventricular ejection • Semilunar valves open • Blood flows into pulmonary and aortic trunks • Stroke volume (SV) = 60% of end-diastolic volume 6. Ventricular pressure falls • Semilunar valves close • Ventricles contain end-systolic volume (ESV), about 40% of end-diastolic volume 41 Ch-20 The Heart Nov-17-2015 The Cardiac Cycle Eight Steps in the Cardiac Cycle 7. Ventricular diastole • Ventricular pressure is higher than atrial pressure • All heart valves are closed • Ventricles relax (isovolumetric relaxation) 8. Atrial pressure is higher than ventricular pressure • AV valves open • Passive atrial filling • Passive ventricular filling • Cardiac cycle ends 42 Ch-20 The Heart Nov-17-2015 The Cardiac Cycle • Heart Sounds (Ausculatation) – S 1 • Loud sounds • Produced by AV valves – S 2 • Loud sounds • Produced by semilunar valves – S 3 S4 • Soft sounds • Blood flow into ventricles and atrial contraction • Heart Murmur – Sounds produced by regurgitation through valves 43 Ch-20 The Heart Nov-17-2015 The Cardiac Cycle Figure 20–18 Heart Sounds 44 Ch-20 The Heart Nov-17-2015 Cardiodynamics • The movement and force generated by cardiac contractions – End-diastolic volume (EDV) – End-systolic volume (ESV) – Stroke volume (SV) • SV = EDV – ESV – Ejection fraction • The percentage of EDV represented by SV – Cardiac output (CO) • The volume pumped by left ventricle in 1 minute ▯ Cardiac Output ▯ CO = HR X SV ▯ CO = cardiac output (mL/min) ▯ HR = heart rate (beats/min) ▯ SV = stroke volume (mL/beat) 45 Ch-20 The Heart Nov-17-2015 Cardiodynamics Figure 20–19 A Simple Model of Stroke Volume 46 Ch-20 The Heart Nov-17-2015 Cardiodynamics Factors Affecting Cardiac Output ▯ Cardiac output ▯ Adjusted by changes in heart rate or stroke volume ▯ Heart rate ▯ Adjusted by autonomic nervous system or hormones ▯ Stroke volume ▯ Adjusted by changing EDV or ESV Figure 20–20 Factors Affecting Cardiac Output 47 Ch-20 The Heart Nov-17-2015 Cardiodynamics • Factors Affecting the Heart Rate – Autonomic innervation • Cardiac plexuses: innervate heart • Vagus nerves (X): carry parasympathetic preganglionic fibers to small ganglia in cardiac plexus • Cardiac centers of medulla oblongata: – cardioacceleratory center controls sympathetic neurons (increases heart rate) – cardioinhibitory center controls parasympathetic neurons (slows heart rate) 48 Ch-20 The Heart Nov-17-2015 Cardiodynamics • Autonomic Innervation – Cardiac reflexes • Cardiac centers monitor: – blood pressure (baroreceptors) – arterial oxygen and carbon dioxide levels (chemoreceptors) – Cardiac centers adjust cardiac activity – Autonomic tone • Dual innervation maintains resting tone by releasing ACh and NE • Fine adjustments meet needs of other systems 49 Ch-20 The Heart Nov-17-2015 Cardiodynamics • Effects on the SA Node ▯ Atrial Reflex – Sympathetic and ▯ Also called Bainbridge reflex parasympathetic stimulation ▯ Adjusts heart rate in response • Greatest at SA node (heart rate) to venous return – Membrane potential of ▯ Stretch receptors in right pacemaker cells atrium • Lower than other cardiac cells ▯ Trigger increase in heart rate – Rate of spontaneous ▯ Through increased depolarization depends on sympathetic activity • Resting membrane potential • Rate of depolarization ▯ Hormonal Effects on HR ▯ Increase heart rate (by sympathetic stimulation of SA node) ▯ Epinephrine (E) ▯ Norepinephrine (NE) ▯ Thyroid hormone 50 Ch-20 The Heart Nov-17-2015 Cardiodynamics Figure 20–21 Autonomic Innervation of the Heart 51 Ch-20 The Heart Nov-17-2015 Cardiodynamics • Factors Affecting the Stroke Volume – The EDV: amount of blood a ventricle contains at the end of diastole • Filling time: – duration of ventricular diastole • Venous return: – rate of blood flow during ventricular diastole • Preload – The degree of ventricular stretching during ventricular diastole – Directly proportional to EDV – Affects ability of muscle cells to produce tension 52 Ch-20 The Heart Nov-17-2015 Cardiodynamics • The EDV and Stroke Volume – At rest ▯ With exercise • EDV is low ▯EDV increases • Myocardium stretches less ▯Myocardium stretches more • Stroke volume is low ▯Stroke volume increases ▯ The Frank–Starling Principle ▯ As EDV increases, stroke volume increases ▯ Physical Limits ▯ Ventricular expansion is limited by ▯ Myocardial connective tissue ▯ The cardiac (fibrous) skeleton ▯ The pericardial sac 53 Ch-20 The Heart Nov-17-2015 Cardiodynamics • End-Systolic Volume (ESV) – The amount of blood that remains in the ventricle at the end of ventricular systole is the ESV • Three Factors That Affect ESV – Preload • Ventricular stretching during diastole – Contractility • Force produced during contraction, at a given preload – Afterload • Tension the ventricle must produce to open the semilunar valve and eject blood 54 Ch-20 The Heart Nov-17-2015 Cardiodynamics • Contractility – Is affected by • Autonomic activity • Hormones • Effects of Autonomic Activity on Contractility – Sympathetic stimulation • NE released by postganglionic fibers of cardiac nerves • Epinephrine and NE released by suprarenal (adrenal) medullae • Causes ventricles to contract with more force • Increases ejection fraction and decreases ESV – Parasympathetic activity • Acetylcholine released by vagus nerves • Reduces force of cardiac contractions 55 Ch-20 The Heart Nov-17-2015 Cardiodynamics Factors Affecting Cardiac Output ▯ Cardiac output ▯ Adjusted by changes in heart rate or stroke volume ▯ Heart rate ▯ Adjusted by autonomic nervous system or hormones ▯ Stroke volume ▯ Adjusted by changing EDV or ESV Figure 20–20 Factors Affecting Cardiac Output 56