Cardiac Physiology 4

8/3/2019 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)

Cardiac Physiology 4

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