cardiac physiology 4
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Cardiac Physiology(IV)
Cardiac Physiology(IV)
A. Rhan Akar
Ankara UniversitySchool of Medicine
December- 2003
A. Rhan Akar
Ankara UniversitySchool of Medicine
December- 2003
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Structure of the HeartStructure of the Heart
adult human heart = 300-350 g
built upon a collagenous skeleton located at
atrioventricular junction (fibrotendinous ring)the ring isolates the atria electrically from theventricles, except at the bundle of His
adult human heart = 300-350 g
built upon a collagenous skeleton located at
atrioventricular junction (fibrotendinous ring)the ring isolates the atria electrically from theventricles, except at the bundle of His
JR Levick, 1995An Introduction to Cardiovascular PhysiologyButterworth-Heinemann
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Cardiac and Skeletal Muscles
Similarities
Cardiac and Skeletal Muscles
Similarities
Both- Striated muscleBoth use proteins actin and myosinBoth contract in response to an actionpotential on the sarcolemmal membrane
Both- Striated muscleBoth use proteins actin and myosinBoth contract in response to an actionpotential on the sarcolemmal membrane
Sperelakis N, Kurachi Y, Terzic A, Cohen MV.Heart Physiology and PathophysiologyAcademic Press, 2001
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Cardiac Muscle F ibers
contractile or conductile
Cardiac Muscle F ibers
contractile or conductile
ContractileAction potential leads to vigorous forcedevelopment and/or mechanical shortening
Conductile
initiation or propagation of actionpotentials
ContractileAction potential leads to vigorous forcedevelopment and/or mechanical shortening
Conductile
initiation or propagation of actionpotentials
Sperelakis N, Kurachi Y, Terzic A, Cohen MV.Heart Physiology and PathophysiologyAcademic Press, 2001
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Conduction System
C onductile Fibers
Conduction System
C onductile Fibers
Sinoatrial (SA) node 100-110/minAtrioventricular (AV) node 40-60/minAV bundle (Bundle of His) 20-40/minLeft and right bundle branchPurkinje fibers ( rapid conduction) 20-40/min
Sinoatrial (SA) node 100-110/minAtrioventricular (AV) node 40-60/minAV bundle (Bundle of His) 20-40/minLeft and right bundle branchPurkinje fibers ( rapid conduction) 20-40/min
Specialised cardiac muscle cells
Noble, D.
Clarendon, Oxford, 1978
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AV node(node of Tawara)irregularly arrangedbranching fibers
Bundle of Hisunbranched fibers
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endotheliumendocardium
Purkinje fibers
Ventricular
myocardium
Purkinje fibers
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Nodal CellsNodal Cells
Smaller than contractile cells or Purkinje cellsLow propagation velocity (0.05m/sec)Reduced density of gap junctionsLack fast Na channels
Smaller than contractile cells or Purkinje cellsLow propagation velocity (0.05m/sec)Reduced density of gap junctionsLack fast Na channels
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E xcitation and Contraction
of Cardiac Myocyte
E xcitation and Contraction
of Cardiac Myocyte
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Suggested reading;The Structure and F unction
of the Cardiac Myocyte:a Review of F undamental Concepts
Sug gested reading;The Structure and F unction
of the Cardiac Myocyte:a Review of F undamental Concepts
Walker CA, Spinale F G.
J Thorac Cardiovasc Surg 1999;118:375-82
Walker CA, Spinale F G.
J Thorac Cardiovasc Surg 1999;118:375-82
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Cardiac MyocyteCardiac Myocyte
Myofiber: is a group of myocytes held together bysurrounding collagen connective tissue
excess collagen,
may cause LV diastolic dysfunction
(e.g. left ventricular hypertrophy)
My ofiber: is a group of myocytes held together bysurrounding collagen connective tissue
excess collagen,
may cause LV diastolic dysfunction
(e.g. left ventricular hypertrophy)
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endotheliumendocardium
Purkinje fibers
Ventricular
myocardium
Purkinje fibers
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Cardiac MyocyteCardiac Myocyte
10-20 Q m in diameter50-100 Q m longsingle central nucleusthe cell is branched, attached to adjacent cellsin an end-to-end fashion (intercalated disc)
desmosomes (proteoglycan glue) gap junction (region of close apposition)
10-20 Q m in diameter50-100 Q m longsingle central nucleusthe cell is branched, attached to adjacent cellsin an end-to-end fashion (intercalated disc)
desmosomes (proteoglycan glue) gap junction (region of close apposition)
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G ap JunctionsG ap Junctions
low resistance connectionssmall pores in the center of each gap junction
allows ions and small peptides to flow from onecell to anotheraction potential is propagated to adjacentmuscle cells
low resistance connectionssmall pores in the center of each gap junction
allows ions and small peptides to flow from onecell to anotheraction potential is propagated to adjacentmuscle cells
Heart behaves as a single motor unit
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SarcomereSarcomere
basic contractile unit within the myocyterefers to the unit from one Z band to the nextresting length:1.8-2.4 Q mcomposed of interdigitating filaments
thick myosin protein thin actin protein
basic contractile unit within the myocyterefers to the unit from one Z band to the nextresting length:1.8-2.4 Q mcomposed of interdigitating filaments
thick myosin protein thin actin protein
Walker CA, Spinale F GJ Thorac Cardiovasc Surg1999, 118:375-82
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Sarcolemma(sarco = flesh; lemma = thin husk)
Sarcolemma(sarco = flesh; lemma = thin husk)
each cell is bounded by a complex cell membrane
composed of a lipid bilayer hydrophilic heads hydrophobic tails
impermeable to charged molecules (barrier fordiffusion)
contains membrane proteins, which include receptors,pumps and channels
each cell is bounded by a complex cell membrane
composed of a lipid bilayer hydrophilic heads hydrophobic tails
impermeable to charged molecules (barrier fordiffusion)
contains membrane proteins, which include receptors,pumps and channels
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F errari R, Opie LH, 1992 Atlas of the myocardiumRaven Press Ltd.
Sarcolemma contains a number of ion channels andpumps that contribute to overall Ca 2+ levels within themyocyte
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Transverse Tubular System
(T-tubules)
Transverse Tubular System
(T-tubules)
the sarcolemma of the myocyte invaginates toform an extensive tubular network
extends the extracellular space into the interiorof the cell
transmit the electrical stimulus rapidly(well developed in ventricular myocytes but isscanty in atrial and Purkinje cells)
the sarcolemma of the myocyte invaginates toform an extensive tubular network
extends the extracellular space into the interiorof the cell
transmit the electrical stimulus rapidly(well developed in ventricular myocytes but isscanty in atrial and Purkinje cells)
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MitochondriaMitochondria
generate the energy in the form of adenosine triphosphate (ATP)maintain the hearts contractile functionand the associated ion gradients
generate the energy in the form of adenosine triphosphate (ATP)maintain the hearts contractile functionand the associated ion gradients
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Sarcoplasmic Reticulum (SR)Sarcoplasmic Reticulum (SR)
a fine network spreading throughout themyocytes
demarcated by its lipid bilayerclose apposition to the T tubules
junctional SR longitudinal SR
a fine network spreading throughout themyocytes
demarcated by its lipid bilayerclose apposition to the T tubules
junctional SR longitudinal SR
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Longitudinal or Network SR Longitudinal or Network SR
consists of ramifying tubules
concerned with the uptake of calcium thatinitiates relaxation
achieved by the ATP-requiring calcium pump(SE RCA= sarcoendoplasmic reticulum Ca 2+ -ATPase)
consists of ramifying tubules
concerned with the uptake of calcium thatinitiates relaxation
achieved by the ATP-requiring calcium pump(SE RCA= sarcoendoplasmic reticulum Ca 2+ -ATPase)