Ch. 12

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Powerpoints for EMS-3000 A & P, Chapter 12, The Heart.

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Ch. 12

  1. 1. Chapter 12The Cardiovascular System: The Heart Bledsoe et al., Anatomy & Physiology for
  2. 2. TopicsIntroductionThe Heart’s Place in the Circulatory SystemThe Anatomy and Organization of the HeartThe HeartbeatHeart Dynamics Bledsoe et al., Anatomy & Physiology for
  3. 3. IntroductionMuscular organ– Beats approximately 100,000 times a day 8,000 liters of blood Bledsoe et al., Anatomy & Physiology for
  4. 4. The Heart’s Placein the Circulatory System Bledsoe et al., Anatomy & Physiology for
  5. 5. The Heart’s Place in the Circulatory SystemBlood flows through a network ofvessels– Extends between the heart and peripheral tissues– Subdivided Pulmonary circuit Systemic circuit Bledsoe et al., Anatomy & Physiology for
  6. 6. The Heart’s Place in the Circulatory SystemPulmonary circuit– Carries blood to and from exchange surfaces of the lungsSystemic circuit– Transports blood to and from the rest of the body Bledsoe et al., Anatomy & Physiology for
  7. 7. The Heart’s Place in the Circulatory SystemCircuits of the circulatory system– Each circuit begins and ends at the heart– Blood travels through each circuit in sequence Blood from systemic circuit must complete pulmonary circuit before returning to systemic circuit Bledsoe et al., Anatomy & Physiology for
  8. 8. The Heart’s Place in the Circulatory SystemArteries– Efferent vessels– Carry blood away from the heart Bledsoe et al., Anatomy & Physiology for
  9. 9. The Heart’s Place in the Circulatory SystemVeins– Afferent vessels– Carry blood to the heart Bledsoe et al., Anatomy & Physiology for
  10. 10. The Heart’s Place in the Circulatory SystemCapillaries– Small, thin-walled vessels– Connect the smallest arteries to the smallest veins Thin walls permit exchange between blood and surrounding tissuesNutrients, dissolved gases, andwastes Bledsoe et al., Anatomy & Physiology for
  11. 11. The Heart’s Place in the Circulatory SystemHeart– Small organ– Contains 4 chambers 2 associated with each circuit Bledsoe et al., Anatomy & Physiology for
  12. 12. The Heart’s Place in the Circulatory SystemHeart– Right atrium Receives blood from systemic circuit– Right ventricle Discharges blood into pulmonary circuit Bledsoe et al., Anatomy & Physiology for
  13. 13. The Heart’s Place in the Circulatory SystemHeart– Left atrium Receives blood from the pulmonary circuit– Left ventricle Discharges blood into the systemic circuit Bledsoe et al., Anatomy & Physiology for
  14. 14. The Heart’s Place in the Circulatory SystemThe beating heart– Atria contract first– Ventricles contract at the same time Eject equal volumes of blood Bledsoe et al., Anatomy & Physiology for
  15. 15. The Anatomy and Organization of the Heart Bledsoe et al., Anatomy & Physiology for
  16. 16. The Anatomy and Organization of the Heart Lies near the anterior chest wall – Directly behind the sternum Bledsoe et al., Anatomy & Physiology for
  17. 17. The Anatomy and Organization of the Heart Enclosed by the mediastinum – Connective tissue mass Divides the thoracic cavity into 2 pleural cavities – Also contains the thymus, esophagus, and trachea Bledsoe et al., Anatomy & Physiology for
  18. 18. The Anatomy and Organization of the Heart Surrounded by the pericardial cavity – Pericardium Serous membrane Lines the pericardial cavity Bledsoe et al., Anatomy & Physiology for
  19. 19. The Anatomy and Organization of the Heart Pericardium – Subdivisions Visceral pericardium Also referred to as the epicardium Covers the outer surface of the heart Parietal pericardium Lines the inner surface of the pericardial sac Bledsoe et al., Anatomy & Physiology for
  20. 20. The Anatomy and Organization of the Heart Pericardial sac – Surrounds the heart – Consists of a dense network of collagen fibers Stabilize the position of the pericardium, heart, and associated vessels Bledsoe et al., Anatomy & Physiology for
  21. 21. The Anatomy and Organization of the Heart Pericardial cavity – Space between the visceral and parietal surfaces – Contains a small quantity of pericardial fluid Secreted by the pericardial membranes Acts as a lubricant Reduces friction between opposing surfaces as the heart beats Bledsoe et al., Anatomy & Physiology for
  22. 22. The Anatomy and Organization of the HeartThe surfaceanatomy of theheart– 2 atria Thin muscular walls Highly expandable Deflates when not filled with blood Forms a lumpy, wrinkled flap called an auricle Bledsoe et al., Anatomy & Physiology for
  23. 23. The Anatomy and Organization of the HeartThe surfaceanatomy of theheart– Coronary sulcus Deep groove Filled with substantial amounts of fat Marks the border between the atria and ventricles Bledsoe et al., Anatomy & Physiology for
  24. 24. The Anatomy and Organization of the HeartThe surface anatomyof the heart– Shallow depressions Anterior interventricular sulcus Posterior interventricular sulcus Mark the boundaries between the left and right ventricles Contain major arteries and veins Supply blood to the cardiac muscle Bledsoe et al., Anatomy & Physiology for
  25. 25. The Anatomy and Organization of the Heart The surface anatomy of the heart – Superior end of the heart Base of the heart Connections for the great veins and arteries of the circulatory system – Inferior portion of the heart Apex Bledsoe et al., Anatomy & Physiology for
  26. 26. The Anatomy and Organization of the HeartThe surface anatomyof the heart– Heart Sits at an angle to the longitudinal axis of the body Slightly rotated to the left Anterior surface consists of right atrium and ventricle Left ventricle forms much of the posterior surface Bledsoe et al., Anatomy & Physiology for
  27. 27. The Anatomy and Organization of the Heart The heart wall – Contains 3 distinct layers Epicardium or visceral pericardium Myocardium Endocardium Bledsoe et al., Anatomy & Physiology for
  28. 28. The Anatomy and Organization of the Heart The heart wall – Epicardium Covers the outer surface of the heart Serous membrane Consists of an exposed epithelium Underlying layer of loose connective tissue Attached to the myocardium Bledsoe et al., Anatomy & Physiology for
  29. 29. The Anatomy and Organization of the Heart The heart wall – Myocardium Muscular wall of the heart Contains: Cardiac muscle tissue Blood vessels Nerves Bledsoe et al., Anatomy & Physiology for
  30. 30. The Anatomy and Organization of the Heart The heart wall – Myocardium Cardiac muscle tissue Forms concentric layers Wraps around the atria Spirals into the walls of the ventricles Bledsoe et al., Anatomy & Physiology for
  31. 31. The Anatomy and Organization of the Heart The heart wall – Cardiac muscle tissue Configuration results in squeezing and twisting contractions Increases the pumping efficiency of the heart Bledsoe et al., Anatomy & Physiology for
  32. 32. The Anatomy and Organization of the Heart The heart wall – Endocardium Covers the heart’s inner surfaces and valves Simple squamous epithelium Continuous with endothelium of attached blood vessels Bledsoe et al., Anatomy & Physiology for
  33. 33. The Anatomy and Organization of the Heart Cardiac muscle cells – Smaller than skeletal muscle fibers – Contain a single, centrally located nucleus – Contain myofibrils Contraction involves shortening of individual sarcomeres Bledsoe et al., Anatomy & Physiology for
  34. 34. The Anatomy and Organization of the Heart Cardiac muscle cells – Almost totally dependent on aerobic metabolism Contain many mitochondria Abundant reserves of myoglobin Store oxygen Energy reserves stored as glycogen and lipids Bledsoe et al., Anatomy & Physiology for
  35. 35. The Anatomy and Organization of the Heart Cardiac muscle cells – Connect with several other cells Specialized sites referred to as intercalated discs Interlocking membranes held together by desmosomes Linked by gap junctions Bledsoe et al., Anatomy & Physiology for
  36. 36. The Anatomy and Organization of the Heart Cardiac muscle cells – Desmosomes Help convey the force of contraction from cell to cell Increase efficiency as they “pull together” during contraction Bledsoe et al., Anatomy & Physiology for
  37. 37. The Anatomy and Organization of the Heart Cardiac muscle cells – Gap junctions Provide for movement of ions and small ions Enable action potentials to travel rapidly between cells Bledsoe et al., Anatomy & Physiology for
  38. 38. The Anatomy and Organization of the Heart Connective tissues in the heart – Include abundant collagen and elastic fibers Wrap around each cardiac muscle cell Tie together adjacent cells – Forms the fibrous skeleton of the heart Bledsoe et al., Anatomy & Physiology for
  39. 39. The Anatomy and Organization of the Heart Connective tissues in the heart – Provide support for cardiac muscle fibers, blood vessels, and nerves of myocardium – Add strength and prevent overexpansion of the heart – Help the heart return to normal shape after contractions Bledsoe et al., Anatomy & Physiology for
  40. 40. The Anatomy and Organization of the Heart Internal anatomy and organization – 4 chambers – 2 atria Separated by an interatrial septum – 2 ventricles Separated by an interventricular septum Bledsoe et al., Anatomy & Physiology for
  41. 41. The Anatomy and Organization of the HeartInternal anatomyand organization– Atrioventricular (AV) valve Opens between the atria and ventricle on the same side Fold of fibrous tissue Ensures a one-way flow of blood Bledsoe et al., Anatomy & Physiology for
  42. 42. The Anatomy and Organization of the HeartInternal anatomy andorganization– Right atrium Receives blood from the systemic circulation Superior vena cava Delivers blood from the head, neck, upper limbs, and chest Inferior vena cava Delivers blood from the trunk, viscera, and lower limbs Bledsoe et al., Anatomy & Physiology for
  43. 43. The Anatomy and Organization of the HeartInternal anatomyand organization– Cardiac veins Return blood to the coronary sinus Opens into the right atrium Slightly below the connection with the inferior vena cava Bledsoe et al., Anatomy & Physiology for
  44. 44. The Anatomy and Organization of the HeartInternal anatomyand organization– Fossa ovalis Small depression Remains of the foramen ovale Bledsoe et al., Anatomy & Physiology for
  45. 45. The Anatomy and Organization of the Heart Internal anatomy and organization – Foramen ovale Oval opening Penetrates the interatrial septum until birth Allows blood to flow between the atria while the lungs are developing Permanently sealed 48 hours after birth Bledsoe et al., Anatomy & Physiology for
  46. 46. The Anatomy and Organization of the Heart Internal anatomy and organization – Foramen ovale May remain open after birth Allows left atrium to push blood back into pulmonary circuit Leads to an enlarged heart May eventually result in heart failure and death Bledsoe et al., Anatomy & Physiology for
  47. 47. The Anatomy and Organization of the HeartInternal anatomy andorganization– Right atrioventricular valve 3 flaps, or cusps, of tissue Surround the broad opening between the right atrium and ventricle Also referred to as the tricuspid valve Bledsoe et al., Anatomy & Physiology for
  48. 48. The Anatomy and Organization of the HeartInternal anatomy andorganization– Right atrioventricular valve Chordae tendineae Connective tissue fibers that brace each cusp Connected to papillary muscles Bledsoe et al., Anatomy & Physiology for
  49. 49. The Anatomy and Organization of the Heart Internal anatomy and organization – Papillary muscles Cone-shaped projections Located on the inner surface of the ventricle Bledsoe et al., Anatomy & Physiology for
  50. 50. The Anatomy and Organization of the Heart Internal anatomy and organization – Papillary muscles contractions Tense the chordae tendineae Limit the movement of the cusps Prevent backflow of blood Bledsoe et al., Anatomy & Physiology for
  51. 51. The Anatomy and Organization of the Heart Internal anatomy and organization – Blood from the right ventricle Flows into the pulmonary trunk Start of the pulmonary circuit Entrance guarded by the pulmonary semilunar valve Bledsoe et al., Anatomy & Physiology for
  52. 52. The Anatomy and Organization of the HeartInternal anatomy andorganization– Pulmonary trunk Blood flows into the left and right pulmonary arteries Branch repeatedly in the lungs Supply the capillaries where gas exchange occurs Referred to as respiratory capillaries Bledsoe et al., Anatomy & Physiology for
  53. 53. The Anatomy and Organization of the Heart Internal anatomy and organization – Pulmonary trunk Oxygenated blood travels from the respiratory capillaries Moves into the left and right pulmonary veins Deliver blood to the left atrium Bledsoe et al., Anatomy & Physiology for
  54. 54. The Anatomy and Organization of the Heart Internal anatomy and organization – Left atrium Has an external auricle Left atrioventricular valve Contains 2 cusps Referred to as the bicuspid or mitral valve Bledsoe et al., Anatomy & Physiology for
  55. 55. The Anatomy and Organization of the HeartInternal anatomy andorganization– Left ventricle Resembles the right ventricle A pair of papillary muscles brace the chordae tendineae Chordae tendineae insert on the cusps Blood passes through the aortic semilunar valve Enters the aorta, starting the systemic circuit Bledsoe et al., Anatomy & Physiology for
  56. 56. The Anatomy and Organization of the Heart Structural differences between the left and right ventricles – Both atria Collect blood returning to the heart Deliver the blood to the attached ventricle Demands of each ventricle are different Bledsoe et al., Anatomy & Physiology for
  57. 57. The Anatomy and Organization of the Heart Structural differences between the left and right ventricles – Right ventricle Lungs are close to the heart Pulmonary veins and arteries are short and wide Does not require much force to propel blood through pulmonary circuit Bledsoe et al., Anatomy & Physiology for
  58. 58. The Anatomy and Organization of the Heart Structural differences between the left and right ventricles – Right ventricle Relatively thin wall Resembles a pouch attached to the wall of the left ventricle Bledsoe et al., Anatomy & Physiology for
  59. 59. The Anatomy and Organization of the Heart Structural differences between the left and right ventricles – Right ventricle Contraction squeezes the blood against the left ventricle Propels it through the pulmonary valve Moves blood efficiently with little effort Develops relatively low pressures Bledsoe et al., Anatomy & Physiology for
  60. 60. The Anatomy and Organization of the Heart Structural differences between the left and right ventricles – Left ventricle Requires 6–7 times more force to propel blood through systemic circuit Has an extremely thick muscular wall Round in cross section Bledsoe et al., Anatomy & Physiology for
  61. 61. The Anatomy and Organization of the Heart Structural differences between the left and right ventricles – Contraction of the left ventricle The distance between the apex and base of the heart decreases Diameter of the ventricular chamber decreases Bulges into the right ventricular cavity Helps force blood out of the right ventricle Bledsoe et al., Anatomy & Physiology for
  62. 62. The Anatomy and Organization of the Heart The heart valves – The atrioventricular valves – The semilunar valves Bledsoe et al., Anatomy & Physiology for
  63. 63. The Anatomy and Organization of the HeartThe atrioventricularvalves– Prevent backflow of blood from the ventricles to the atria– At rest Chordae tendineae are loose AV valve offers no resistance to blood flow from the atrium to the ventricle Bledsoe et al., Anatomy & Physiology for
  64. 64. The Anatomy and Organization of the HeartThe atrioventricularvalves– Ventricular contraction Blood moves back toward the atrium Forces the cusps together Closes the valve Bledsoe et al., Anatomy & Physiology for
  65. 65. The Anatomy and Organization of the Heart The atrioventricular valves – Ventricular contraction Tension in papillary muscles and chordae tendineae Keeps cusps from swinging into the atrium Prevents regurgitation of blood into the atrium Bledsoe et al., Anatomy & Physiology for
  66. 66. The Anatomy and Organization of the Heart The atrioventricular valves – Regurgitation May occur in small amounts Even in normal individuals Swirling blood creates a distinctive sound Referred to as a heart murmur Bledsoe et al., Anatomy & Physiology for
  67. 67. The Anatomy and Organization of the HeartThe semilunar valves– Prevent backflow of blood from the pulmonary trunk and aorta– Do not require muscular bracing Arterial walls do not contract Relative positions of the cusps are stable Bledsoe et al., Anatomy & Physiology for
  68. 68. The Anatomy and Organization of the Heart The semilunar valve – Closing 3 symmetrical cusps support each other Prevent the backflow of blood into the ventricles Bledsoe et al., Anatomy & Physiology for
  69. 69. The Anatomy and Organization of the HeartAortic sinuses– Saclike expansions of the base of the ascending aorta– Found next to each cusp– Prevent the cusps from sticking to the wall of the aorta when opening Origin for the right and left coronary arteries Bledsoe et al., Anatomy & Physiology for
  70. 70. The Anatomy and Organization of the Heart The blood supply to the heart – Heart works continuously – Requires a reliable supply of oxygen and nutrients Supplied by the coronary circulation Bledsoe et al., Anatomy & Physiology for
  71. 71. The Anatomy and Organization of the Heart The blood supply to the heart – Right and left coronary arteries Originate at the base of the aorta At the aortic sinuses Highest blood pressure of the systemic circuit Ensures continuous blood flow to the heart Bledsoe et al., Anatomy & Physiology for
  72. 72. The Anatomy and Organization of the Heart The blood supply to the heart – Right coronary artery (RCA) Supplies blood to the right atrium Supplies blood to portions of both ventricles Bledsoe et al., Anatomy & Physiology for
  73. 73. The Anatomy and Organization of the Heart The blood supply to the heart – Left coronary artery (LCA) Supplies blood to the left ventricle Left atrium Interventricular septum Bledsoe et al., Anatomy & Physiology for
  74. 74. The Anatomy and Organization of the Heart The blood supply to the heart – 2 branches of the right coronary artery Marginal branch Posterior interventricular (descending) branch Bledsoe et al., Anatomy & Physiology for
  75. 75. The Anatomy and Organization of the Heart The blood supply to the heart – 2 branches of the left coronary artery Circumflex branch Anterior interventricular (descending) branch Bledsoe et al., Anatomy & Physiology for
  76. 76. The Anatomy and Organization of the Heart The blood supply to the heart – Anastomoses Interconnections Occur between small tributaries from the branches of the left and right coronary arteries Create alternate pathways for blood supply Bledsoe et al., Anatomy & Physiology for
  77. 77. The Anatomy and Organization of the HeartThe blood supply to the heart – Great and middle cardiac veins Carry blood away from the coronary capillaries Drain into the coronary sinus Bledsoe et al., Anatomy & Physiology for
  78. 78. The Anatomy and Organization of the HeartThe blood supply tothe heart– Coronary sinus Large, thin-walled vein Located in the posterior portion of the coronary sulcus Opens into the right atrium Near the base of the inferior vena cava Bledsoe et al., Anatomy & Physiology for
  79. 79. The Anatomy and Organization of the Heart The blood supply to the heart – Infarct Area of dead tissue Caused by interruption in blood flow Bledsoe et al., Anatomy & Physiology for
  80. 80. The Anatomy and Organization of the Heart The blood supply to the heart – Myocardial infarction Coronary circulation becomes blocked Cardiac muscle cells die from a lack of oxygen Most often occurs as a result of coronary artery disease Build-up of fatty deposits in the walls of the coronary arteries Bledsoe et al., Anatomy & Physiology for
  81. 81. The HeartbeatBledsoe et al., Anatomy & Physiology for
  82. 82. The HeartbeatAtria and ventricles contract in acoordinated mannerCauses blood to flow in the correctdirection at the proper timeCardiac muscle cells must contract ina specific sequence Bledsoe et al., Anatomy & Physiology for
  83. 83. The Heartbeat2 types of cardiac muscle cells– Contractile cells Produce powerful contractions that propel blood– Specialized noncontractile muscle cells Part of the conducting system Control and coordinate activities of contractile cells Bledsoe et al., Anatomy & Physiology for
  84. 84. The HeartbeatContractile cells– Form the bulk of the heart’s muscle tissue Action potential leads to calcium among the myofibrils Binds to troponin on thin filaments Begins a contraction Bledsoe et al., Anatomy & Physiology for
  85. 85. The HeartbeatContractile cells– Differences between cardiac muscle cells Duration of action potentials Source of calcium Duration of the resulting contraction Bledsoe et al., Anatomy & Physiology for
  86. 86. The HeartbeatContractile cells– Action potential in ventricular muscle cells Begins when the membrane is brought to threshold Stimulus typically comes from the excitation of an adjacent cell Proceeds in 3 steps Bledsoe et al., Anatomy & Physiology for
  87. 87. The HeartbeatContractile cells– Step 1: Rapid depolarization At threshold, sodium channels open Influx of sodium depolarizes the sarcolemma Sodium channels close when transmembrane potential reaches +30 mV Bledsoe et al., Anatomy & Physiology for
  88. 88. The HeartbeatContractile cells– Step 2: The plateau Cell begins to actively pump sodium out Calcium channels open Extracellular calcium ions enter sarcoplasm Channels remain open for a relatively long period Calcium gain roughly balances sodium loss Bledsoe et al., Anatomy & Physiology for
  89. 89. The HeartbeatContractile cellsStep 2: The plateau– Functions of calcium Delay repolarization Maintain the transmembrane potential near 0 mV The plateau Initiate contraction Concentration triggers release of calcium reserves from sarcoplasmic reticulum Continues the contraction Bledsoe et al., Anatomy & Physiology for
  90. 90. The HeartbeatContractile cells– Step 3: Repolarization Calcium channels begin to close Potassium channels open Potassium rushes out of the cell Restores the resting potential Bledsoe et al., Anatomy & Physiology for
  91. 91. The HeartbeatContractile cells– Phases Bledsoe et al., Anatomy & Physiology for
  92. 92. The HeartbeatContractile cells– Action potential Prolonged when compared to skeletal muscles Due to calcium flow during plateau Contraction continues until plateau ends Bledsoe et al., Anatomy & Physiology for
  93. 93. The HeartbeatContractile cells– Action potential Calcium channels close Calcium absorbed by the SR or pumped out of the cell Muscle cell relaxes Bledsoe et al., Anatomy & Physiology for
  94. 94. The HeartbeatContractile cells– Depolarization- repolarization process Lasts 250–300 msec Membrane cannot respond to further stimulation until repolarized Creates a long refractory period Bledsoe et al., Anatomy & Physiology for
  95. 95. The HeartbeatContractile cells– Refractory period Continues until relaxation is underway Prevents summation of twitches that occurs in skeletal muscles Does not permit tetany Heart could not pump blood in tetany Bledsoe et al., Anatomy & Physiology for
  96. 96. The HeartbeatThe conducting system– Cardiac muscle tissue contracts on its own In the absence of neural or hormonal stimuli Referred to as automaticity Bledsoe et al., Anatomy & Physiology for
  97. 97. The HeartbeatThe conducting system– Each contraction should follow a precise sequence Atria contract first Followed by the ventricles Bledsoe et al., Anatomy & Physiology for
  98. 98. The HeartbeatThe conducting system– Coordinates contractions– Network of specialized cardiac muscle cells Initiate and distribute electrical impulses 2 types of cells that do not contract Nodal cells Conducting cells Bledsoe et al., Anatomy & Physiology for
  99. 99. The HeartbeatThe conductingsystem– Nodal cells Responsible for establishing the rate of cardiac contraction Locations Sinoatrial node Atrioventricular node Bledsoe et al., Anatomy & Physiology for
  100. 100. The HeartbeatThe conductingsystem– Conducting cells Distribute the contractile stimulus to the general myocardium Major locations AV bundle Bundle branches Purkinje fibers Bledsoe et al., Anatomy & Physiology for
  101. 101. The HeartbeatNodal cells– Cell membranes depolarize spontaneously– Generate action potentials at regular intervals– Electrically coupled to each other, conducting cells, and normal cardiac muscle cells– Determine heart rate Bledsoe et al., Anatomy & Physiology for
  102. 102. The HeartbeatNodal cells– Action potential initiated in nodal cells– Progresses through the conducting system– Reaches all cardiac muscle tissue– Results in a coordinated contraction Bledsoe et al., Anatomy & Physiology for
  103. 103. The HeartbeatNodal cells– Not all nodal cells depolarize at the same rate– Normal rate of contraction Established by pacemaker cells Nodal cells that reach threshold first Located in the sinoatrial (SA) node Bledsoe et al., Anatomy & Physiology for
  104. 104. The HeartbeatSA node– Referred to as the cardiac pacemaker– Tissue mass embedded in the wall of the right atrium Near the entrance to the superior vena cava– Depolarize rapidly and spontaneously Generate 70–80 action potentials per minute Bledsoe et al., Anatomy & Physiology for
  105. 105. The HeartbeatSA node– Distribution of stimulus for contraction Atria must contract together Before the ventricles Ventricles contract together Begins at the apex, spreading toward the base Pushes blood into the aorta and pulmonary trunk Bledsoe et al., Anatomy & Physiology for
  106. 106. The HeartbeatSA node cells– Electrically connected to the large atrioventricular (AV) node Through conducting cells in the atrial walls Bledsoe et al., Anatomy & Physiology for
  107. 107. The HeartbeatAV node– Also depolarize spontaneously Generate only 40–60 action potentials per minute– Normal contractions Stimulated by the SA node action potential Occur before AV cell depolarizes to threshold spontaneously Bledsoe et al., Anatomy & Physiology for
  108. 108. The HeartbeatAV node– If action potential not received from SA node AV node becomes the pacemaker of the heart Establishes a heart rate of 40–60 beats per minute Bledsoe et al., Anatomy & Physiology for
  109. 109. The HeartbeatAV node– Located in the floor of the right atrium Near the opening of the coronary sinus– Action potential travels to the AV bundles Referred to as the bundle of His Bledsoe et al., Anatomy & Physiology for
  110. 110. The HeartbeatBundle of His– Conducting cells– Extend along the interventricular septum– Divide into the left and right bundle branches Bledsoe et al., Anatomy & Physiology for
  111. 111. The HeartbeatBundle branches– Radiate across the inner surfaces of the ventricles– Transfer impulses to the Purkinje fibers Bledsoe et al., Anatomy & Physiology for
  112. 112. The HeartbeatPurkinje fibers– Specialized cells– Convey impulses to the contractile cells of the ventricular myocardium Bledsoe et al., Anatomy & Physiology for
  113. 113. The HeartbeatAction potential– Takes 50 msec to travel from the SA node to the AV node Occurs over conducting pathways Conducting cells pass contractile stimulus to cardiac muscle cells of the left and right atrium Spreads across atrial surfaces through cell-to-cell contact Bledsoe et al., Anatomy & Physiology for
  114. 114. The HeartbeatAction potential– Impulse affects only the atria Fibrous skeleton electrically isolates the atria from the ventricles Except at the AV bundle Bledsoe et al., Anatomy & Physiology for
  115. 115. The HeartbeatAction potential– Impulse slows down at the AV node 100 msec pass before impulse reaches the AV bundle Delay allows the atria to contract and move blood before ventricular stimulation Bledsoe et al., Anatomy & Physiology for
  116. 116. The HeartbeatAction potential– Impulse enters the AV bundle– Continues down the interventricular septum– Proceeds along the bundle branches– Spreads through the ventricular myocardium along Purkinje fibers Bledsoe et al., Anatomy & Physiology for
  117. 117. The HeartbeatAction potential– Stimulus to begin a contraction Reaches all ventricular muscle cells Occurs within another 75 msec Bledsoe et al., Anatomy & Physiology for
  118. 118. The HeartbeatDeviations from normal pacemakerfunction– Bradycardia is where the heart is beating slower than normal Less than 60 bpm– Tachycardia is where the heart is beating faster than normal Greater than 100 bpm Bledsoe et al., Anatomy & Physiology for
  119. 119. The HeartbeatDeviations from normal pacemakerfunction– Overriding SA or AV node Caused by an abnormal conducting cell or ventricular muscle cell Generates action potentials too rapid for normal function Origin is referred to as an ectopic pacemaker Bledsoe et al., Anatomy & Physiology for
  120. 120. The HeartbeatDeviations from normal pacemakerfunction– Overriding SA or AV node Action potentials may completely bypass the conducting system Disrupts the timing of ventricular contractions Diagnosed with an electrocardiogram Bledsoe et al., Anatomy & Physiology for
  121. 121. The HeartbeatThe electrocardiogram– Recording of the electrical events in the heart Can be detected on the body surface– Also referred to as an ECG or EKG Bledsoe et al., Anatomy & Physiology for
  122. 122. The HeartbeatThe electrocardiogram– Each time the heart beats Wave of depolarization radiates through the atria Reaches the AV node Travels down the interventricular septum Reaches the apex and turns Spreads through the ventricular myocardium toward the base Bledsoe et al., Anatomy & Physiology for
  123. 123. The HeartbeatThe electrocardiogram– Electrodes are placed at different locations on the chest– Information compared– Allows monitoring of specific nodal, conducting, and contractile components Bledsoe et al., Anatomy & Physiology for
  124. 124. The HeartbeatThe electrocardiogram– Damaged heart tissue Affected muscle cells no longer conduct an action potential ECG reveals abnormal pattern of impulse conduction Bledsoe et al., Anatomy & Physiology for
  125. 125. The HeartbeatThe electrocardiogram– Appearance varies with the placement of the monitoring electrodes Referred to as leads Standard configurations Bledsoe et al., Anatomy & Physiology for
  126. 126. The HeartbeatThe electrocardiogram– Important ECG features P wave Small wave Created by depolarization of the atria Atria begin contracting about 100 msec after the start of the P wave Bledsoe et al., Anatomy & Physiology for
  127. 127. The HeartbeatThe electrocardiogram– Important ECG features QRS complex Occurs when ventricles depolarize Relatively strong signal Ventricular muscle larger than atrial muscle Ventricles begin contracting shortly after the peak of the R wave Bledsoe et al., Anatomy & Physiology for
  128. 128. The HeartbeatTheelectrocardiogram– Important ECG features T wave Smaller wave Indicates ventricular repolarization Bledsoe et al., Anatomy & Physiology for
  129. 129. The HeartbeatThe electrocardiogram– Atrial repolarization Not visible Occurs while the ventricles are depolarizing Electrical events are masked by the QRS complex Bledsoe et al., Anatomy & Physiology for
  130. 130. The HeartbeatTheelectrocardiogram Bledsoe et al., Anatomy & Physiology for
  131. 131. The HeartbeatAnalysis of the ECG– Measuring the size of the voltage changes Small electrical signals may mean a decrease in heart muscle mass Excessively large signals may indicate enlargement– Determining the temporal relationships of various components Bledsoe et al., Anatomy & Physiology for
  132. 132. The HeartbeatAnalysis of the ECG– Used to detect and diagnose cardiac arrhythmias Abnormal patterns of cardiac activity Clinically important when they reduce the pumping efficiency Bledsoe et al., Anatomy & Physiology for
  133. 133. The HeartbeatCardiac arrhythmias– Indicative of: Damage to the myocardium Injuries to the pacemaker or conduction pathways Exposure to drugs Variations in electrolyte concentrations Bledsoe et al., Anatomy & Physiology for
  134. 134. The HeartbeatThe cardiac cycle– The period between the start of one beat and the start of the next– Includes both contraction and relaxation– Each chamber of the heart can be divided into 2 phases Bledsoe et al., Anatomy & Physiology for
  135. 135. The Heartbeat2 phases of the cardiac cycle– Systole Contraction Chamber squeezes blood into adjacent chamber or arterial trunk– Diastole Relaxation Chamber fills with blood Prepares for the next cycle Bledsoe et al., Anatomy & Physiology for
  136. 136. The HeartbeatThe cardiac cycle– Fluid flows from high pressure to low pressure Pressure in the chamber rises with systole Pressure in the chamber falls during diastole Pressure increase in one chamber causes blood to flow into another chamber or vessel Bledsoe et al., Anatomy & Physiology for
  137. 137. The HeartbeatThe cardiac cycle– Pressure relationships in the heart Maintained by careful timing of contractions Pacemaking and conduction system provides required intervals Bledsoe et al., Anatomy & Physiology for
  138. 138. The HeartbeatThe cardiac cycle– Begins with atrial systole Ventricles are already partly filled with blood Roughly 70% Atria contract to completely fill the ventricle Bledsoe et al., Anatomy & Physiology for
  139. 139. The HeartbeatThe cardiac cycle– Atrial systole ends– Atrial diastole and ventricular systole begin Pressure rises in the ventricles AV valves swing shut Bledsoe et al., Anatomy & Physiology for
  140. 140. The HeartbeatThe cardiac cycle– Ventricular pressure must exceed arterial pressure for blood to move– Blood pushes semilunar valves open Blood flows into the aorta and pulmonary trunk– Blood flow continues for the duration of ventricular systole Bledsoe et al., Anatomy & Physiology for
  141. 141. The HeartbeatThe cardiac cycle– Ventricular diastole begins– Ventricular pressure rapidly declines– Semilunar valves close when arterial pressure exceeds ventricular pressure Bledsoe et al., Anatomy & Physiology for
  142. 142. The HeartbeatThe cardiac cycle– Ventricular pressure continues to drop Eventually falls below atrial pressure– AV valves open– Blood flows from the atria to the ventricles Passive Both the atria and ventricles are in diastole Bledsoe et al., Anatomy & Physiology for
  143. 143. The HeartbeatThe cardiac cycle Bledsoe et al., Anatomy & Physiology for
  144. 144. The HeartbeatHeart sounds– 4 heart sounds– “Lubb-dupp” Accompany actions of the heart valves First part produced when AV valves close and semilunar valves open Second part occurs when semilunar valves close Bledsoe et al., Anatomy & Physiology for
  145. 145. The HeartbeatHeart sounds– Third and fourth heart sounds Faint and seldom detectable Associated with atrial contraction and blood flowing into ventricles Bledsoe et al., Anatomy & Physiology for
  146. 146. Heart Dynamics Bledsoe et al., Anatomy & Physiology for
  147. 147. Heart DynamicsRefers to the movements and forcesgenerated during cardiac contractions– Ventricles eject equal amounts of blood Stroke volume (SV) is the amount ejected by 1 ventricle Can vary from beat to beat Cardiac output (CO) is the amount pumped by each ventricle in 1 minute Provides an indication of the blood flow through peripheral tissues Bledsoe et al., Anatomy & Physiology for
  148. 148. Heart DynamicsCalculating cardiac output– Multiple the average stroke volume by the heart rate (HR) CO (ml/minute) = SV (ml/beat) x HR (beats/min) Bledsoe et al., Anatomy & Physiology for
  149. 149. Heart DynamicsCardiac output– Roughly equivalent to the total blood volume of an average adult– Highly variable HR and SV can increase together CO increases 500–700 % Bledsoe et al., Anatomy & Physiology for
  150. 150. Heart DynamicsFactors controlling cardiac output– Regulated so peripheral tissues receive adequate blood supply– Major factors affect both HR and SV Blood volume reflexes Autonomic innervation Hormones Bledsoe et al., Anatomy & Physiology for
  151. 151. Heart DynamicsFactors controlling cardiac output– Secondary factors Ion concentrations in extracellular fluids Body temperature Bledsoe et al., Anatomy & Physiology for
  152. 152. Heart DynamicsBlood volume reflexes– Cardiac muscle contraction is active process– Relaxation is passive Force required to return cardiac muscle to precontracted length Provided by blood pouring into heart Aided by elasticity of fibrous skeleton Bledsoe et al., Anatomy & Physiology for
  153. 153. Heart DynamicsBlood volume reflexes– Direct relationship Amount of blood entering the heart Amount of blood ejected with next contraction Bledsoe et al., Anatomy & Physiology for
  154. 154. Heart DynamicsBlood volume reflexes– 2 heart reflexes respond to changes in blood volume Right atrium reflex affects heart rate Ventricular reflex affects stroke volume Bledsoe et al., Anatomy & Physiology for
  155. 155. Heart DynamicsAtrial reflex– Bainbridge reflex– Adjusts HR in response to venous return Flow of venous blood into the heart Bledsoe et al., Anatomy & Physiology for
  156. 156. Heart DynamicsBainbridge reflex– Entry of blood stimulates stretch receptors in right atrial wall– Reflexive increase in heart rate triggered Increase in sympathetic activity– Sympathetic stimulation causes an increase in SA node discharge Bledsoe et al., Anatomy & Physiology for
  157. 157. Heart DynamicsStroke volume depends on:– Venous return– Filling time Bledsoe et al., Anatomy & Physiology for
  158. 158. Heart DynamicsFilling time– Duration of ventricular diastole– Depends primarily on heart rate The faster the HR, the shorter the filling time Bledsoe et al., Anatomy & Physiology for
  159. 159. Heart DynamicsChanges in venous return– Alterations in cardiac output– Alterations in peripheral circulation– Factors that affect blood flow through the venae cavae Bledsoe et al., Anatomy & Physiology for
  160. 160. Heart DynamicsVentricular reflex– Frank-Starling principle More in = more out Bledsoe et al., Anatomy & Physiology for
  161. 161. Heart DynamicsFrank-Starling principle– The greater the volume that enters the ventricles– The more powerful the contraction– The greater the stroke volume Bledsoe et al., Anatomy & Physiology for
  162. 162. Heart DynamicsFrank-Starling principle– Venous return increases– Ventricular myocardium stretches more– Ventricles produce a stronger contraction Bledsoe et al., Anatomy & Physiology for
  163. 163. Heart DynamicsAutonomic innervation– SA node pacemaker cells establish basic heart rate– Rate modified by autonomic nervous system Both the sympathetic and parasympathetic divisions Bledsoe et al., Anatomy & Physiology for
  164. 164. Heart DynamicsAutonomic innervation– Postganglionic sympathetic fibers Extend from neuron cell bodies in cervical and upper thoracic ganglia– Preganglionic parasympathetic fibers Carried on the vagus nerve Extend to small ganglia near the heart Bledsoe et al., Anatomy & Physiology for
  165. 165. Heart DynamicsAutonomic innervation– ANS divisions Innervate the SA and AV nodes Innervate atrial and ventricular cardiac muscle cells Bledsoe et al., Anatomy & Physiology for
  166. 166. Heart DynamicsAutonomicinnervation Bledsoe et al., Anatomy & Physiology for
  167. 167. Heart DynamicsAutonomic effects on heart rate– Primarily reflect SA node responses to ACh and NE– ACh released by parasympathetic motor neurons Lower the heart rate– NE released by sympathetic neurons Increase the heart rate Bledsoe et al., Anatomy & Physiology for
  168. 168. Heart DynamicsAutonomic effects on heart rate– Sustained rise in heart rate Sympathetic activation of adrenal medullae Release of epinephrine and norepinephrine Bledsoe et al., Anatomy & Physiology for
  169. 169. Heart DynamicsAutonomic effects on stroke volume– Release of NE, E, and ACh Alters the force of myocardial contraction Bledsoe et al., Anatomy & Physiology for
  170. 170. Heart DynamicsThe effects of NE and E– Sympathetic release of NE in the myocardium– Release of NE and E by adrenal medullae Stimulates cardiac muscle cell metabolism Increases the force and degree of contraction Results in increased stroke volume Bledsoe et al., Anatomy & Physiology for
  171. 171. Heart DynamicsThe effects of ACh– Parasympathetic ACh release Inhibition Results in a decrease in the force of cardiac contraction Limited innervation in the ventricles Greatest reduction in force occurs in the ventricles Bledsoe et al., Anatomy & Physiology for
  172. 172. Heart DynamicsBlocking the vagus nerve– Increases the heart rateBlocking the sympathetic nervoussystem– Slows the heart rate Bledsoe et al., Anatomy & Physiology for
  173. 173. Heart DynamicsThe coordination of autonomic activity– Autonomic headquarters for cardiac control Cardiac centers of the medulla oblongata Cardioacceleratory center activates sympathetic motor neurons Cardioinhibitory center controls parasympathetic motor neurons Bledsoe et al., Anatomy & Physiology for
  174. 174. Heart DynamicsThe coordination of autonomic activity– Cardiovascular information Arrives at cardiac centers Sensory fibers from the vagus nerve Sympathetic fibers nerves of the cardiac plexus Bledsoe et al., Anatomy & Physiology for
  175. 175. Heart DynamicsThe coordination of autonomic activity– Cardiac center response Changes in blood pressure Arterial concentrations of dissolved oxygen and carbon dioxide Bledsoe et al., Anatomy & Physiology for
  176. 176. Heart DynamicsThe coordination of autonomic activity– Monitors baroreceptors and chemoreceptors Innervated by glossopharyngeal and vagus nerves Bledsoe et al., Anatomy & Physiology for
  177. 177. Heart DynamicsThe coordination of autonomic activity– Decline in blood pressure or oxygen, or an increase in carbon dioxide Indicates oxygen demand of peripheral tissues has increased– Cardiac centers increase cardiac output Bledsoe et al., Anatomy & Physiology for
  178. 178. Heart DynamicsHormones– Thyroid hormones and glucagon also increase the force of contraction– Digitalis Increases calcium concentration Results in an increase in the force of contraction– Antihypertensives Have a negative effect on contractility Bledsoe et al., Anatomy & Physiology for
  179. 179. SummaryDescribe the location and features of theheartUnderstand the flow of blood through theheartDescribe the components of the conductionsystemUnderstand how the conduction systemfunctionsDescribe the cardiac cycleUnderstand the factors that influencecardiac output Bledsoe et al., Anatomy & Physiology for

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