Blood Flow

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crzhazen
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68109
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Blood Flow
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2011-02-22 10:34:59
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Blood Flow
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Blood Flow
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  1. Coronary Circulation
    • 5% of blood pumped by heart is pumped to heart itself
    • Abundant cardiac muscles need lots of oxygen and nutrients
  2. Left Coronary Artery
    • Branches off Aorta
    • Anterior interventricular branch: supplies ventricles and parts of interventricular septum
    • Circumflex branch: lies in coronary sulcus; supplies left atrium and posterior left ventricle
  3. Right Coronary Artery
    • Branches off Aorta
    • Supplies sinoastrial node (pacemaker)
    • Right Marginal Branch: supplies lateral right atrium and ventricle
    • Poster Interventricular Branch: supplies posterior ventricles
  4. Coronary Veins
    Some blood drains directly into right atrium and right ventricle
  5. Coronary Sinus
    • Huge vein in coronary sulcus on posterior side that collects blood and empties into right atrium
    • Great Cardiac Vein: collects blood from anterior heart, empties into coronary sinus
    • Middle Cardiac Vein: collects blood from posterior heart, empties into coronary sinus
    • Left Marginal Vein: Empties into coronary sinus
  6. Coronary Artery Disease (CAD)
    Blockage of coronary arteries (ischemia) typically caused by atherosclerotic plaque formation
  7. Myocardial Infarction (Heart Attack)
    • Caused by coronary ischemia
    • Cardiac muscle downstream of blockage dies
    • Cardiac cells can die within minutes
    • Built-in protection from MI: arterial anastomoses provide many routes for blood to reach all parts of heart (collateral circulation)
  8. Angina Pectoris
    • Chest pain from partial obstruction of coronary blood flow
    • Pain caused by ischemia of cardiac muscle
    • Myocardium shifts to fermentation and produces lactic acid, which causes pain.
  9. MI Treatment
    • Reduce risk factors: stop smoking, modify diet, reduce stress, increase exercise
    • Drug treatment: reduce coagulation (aspirin, coumadin), block sympathetic stimulation (propranolol), cause vasodilation (nitroglycerin)
    • Surgery:
    • Artherectomy: plaque removal through catheter
    • Balloon Angioplasty: Pressing plaque against vessel walls
    • Coronary Artery Bypass: create detour around blockage
  10. Cardiac Physiology
    • Contractile Muscle Cells: produce heart contractions
    • Conducting System: nodes generate electrical signals; conducting cells distribute electrical signals between nodes and to remainder of heart
  11. Cardiac Muscle
    • Cardiocytes: short muscle cells, striated, one nucleus, lots of glycogen surrounding it.
    • Intercalated disks: join cardiocytes together
    • Interdigitating folds: interlock cells together
    • Mechanical junctions: tightly join cardiocytes
    • Gap junctions: allow ions to flow between cells
  12. Cardiac Conduction
    • Coordinates heartbeat
    • Internal pacemaker and conduction pathways through myocardium
    • Pathway of electrical signal: sinaotrial node, atrioventricular node, atrioventricular bundle, the purkinje fibers
    • Signals pass for cell to cell through gap junctions
  13. Sinoatrial Node
    • Modified cardiocytes in right atrium, near superior vena cava
    • Pacemaker cells initiate heartbeat
    • Pace determines heart rate
    • Spreads signal throughout both atria
  14. Atrioventricular Node
    • Near right AV valve
    • Excited by SA node firing, then allows for the excitement of cardiocytes in ventricles
    • Provides delay: don't want atria and ventricles contracting at same time
  15. AV Bundle
    • Bundle of cells from AV node to apex of heart
    • Transmits electrical signal to apex
  16. Purkinje Fibers
    Nerve-like projections that spread throughout ventricular myocardium
  17. Parasympathetic NS Innervation of Heart
    • Vagus nerves terminate in SA and AV nodes
    • Slow heart rate
    • At rest, parasympathetic NS is active: without activity, heart beat is 80-100 bpm instead of the typical 60-80 bpm
    • Parasympathetic released ACh onto SA node, which opens K+ channels and decreases frequency of spontaneous depolarizations
  18. Sympathetic NS Innervation of Heart
    • Fibers terminate is SA and AV nodes; in atrial and ventricular myocardium; in aorta, pulmonary trunk, coronary arteries
    • Increases heart rate and dilate coronary arteries (more blood flow to heart)
    • Norepinephrine released by sympathetic NS makes spontaneous depolarization in SA node more frequent
  19. Baroreceptors
    Monitor blood volume for autonomic nervous system
  20. Cardiac Rhythms
    • Cycle of Events
    • Systole: atrial or ventricular contraction
    • Diastole: arial or ventricular relaxation
  21. Sinus Rhythm
    • Normal heartbeat triggered by SA node
    • Typically 60-100 beats per minute
  22. Ectopic Focus
    • Spontaneous firing from something other than the SA node
    • Nodal Rhythm: AV node sets rate at 40-50 bpm if SA node is damaged
    • Intrinsic Ventricular Rhythm: if both nodes are damaged, heart rate is 20-40 bpm (need pacemaker)
  23. Arrhythmia
    • Any abnormal rhythm
    • Atrial flutter: atria beat 200-400 bpm (atrial fibrillation)
    • Premature ventricular contractions caused by stimulants, stress, and lack of sleep
    • Ventricular Fibrillation: electrical signals reach parts of ventricles at different times and can't pump blood
    • Defibrillation: electrical shock to depolarize entire heart and reset SA nodes to sinus rhythm
  24. SA Node Potentials
    • No resting potential
    • Repeating cycle of depolarizations
  25. SA Node Physiology
    • Initially depolarizes due to influx of Na+ (“pacemaker potential”)
    • At threshold (-40 mV), fast Ca2+ and Na+ channels open
    • Fast depolarization peaks at 0 mV
    • Opening of K channels hyperpolarizes membrane
    • K channels close, then cycle starts over
    • Each depolarization causes heart contraction
  26. Spread from SA Node
    • SA node depolarization spreads to atrial muscle cells and AV node through gap junctions
    • AV node also has pacemaker-like activity, but it’s slow and SA node speeds it up
  27. Spread Past AV Node
    • Action potential spreads down AV bundle and Purkinje fibers
    • Papillary muscles contract just before ventricles to tighten slack in chordae tendinae
    • Contraction begins at apex, then twisting upwards
  28. Myocardial Cells
    • Stable resting potential of -90mV
    • Depolarize only when stimulated
    • Depolarization phase: stimulus opens Na+ channels, quick depolarization, then Na+ channels close
    • Plateau Phase: Ca2+ channels open, cause sarcoplasmic reticulum to release more Ca2+, sustains contraction
    • Repolarization Phase: Ca2+ channels close, K+ close to return to resting potential

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