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Organisation of the Body

Quiz yourself by thinking what should be in each of the black spaces below before clicking on it to display the answer.
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Question
Answer
What is the heart   show
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What is cardiac output and how is it regulated   show
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Gross structure of the heart   show
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show Ventricular - brick like appearance with striations, mono-nucleated to provide the contraction force Atrial - smaller as less force is needed, still striated SAN - very thin, no sarcomeric structures, key cells in the pacemaker  
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Ultrastructure of myocardium   show
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show Make of connexin 43, 6 monomers form a connexon tunnel which spans the membrane projecting into the extracellular space where it connects to connexons of adjacent cells This allows movement of ions and hormones between myocytes  
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Organisation of contractile filaments   show
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show The greater the filling of the cardiac chamber the greater individual myocardial fibres are stretched, hence the greater the subsequent force of contraction Small changes in size of a myocyte will therefor produce large changes in force generated  
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show Generated in the SAN, cannot go directly to the ventricles so must pass through the AVN. This ensures the atria contract before the ventricles Action potential is prolonged, so the muscle fully relaxes before another AP can be generated  
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Different Action Potential shapes   show
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show Pacemaker function - myogenic rhythm Fast/slow conduction to synchronise contraction Long plateau to maintain refractoriness and avoid high frequency activation  
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Phases of the Action potential in the SAN   show
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What are HCN channels   show
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What sets the pacemaker current   show
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Phases of the action potential in ventricular myocytes   show
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Excitation contraction coupling   show
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show This is used to exclude calcium from myocytes following contraction This is an electrogenic pump as per Ca extruded 3 Na move in leading to a positive inwards flow The Na/K pump helps to maintain the Na gradient and offset this  
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Action of Ouabain   show
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show Adding a Ca2+ dye to a cardiac myocyte reveals a Ca2+ wave on excitation, which moves through the cell allowing for synchronous contraction  
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show The rise in [Ca2+] in normal cardiomyocytes during a beat is only large enough to produce a fraction of the intrinsically available strength (50%) The strength of contraction can be increased by increments of [Ca2+] attained via ionotropic interventions  
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show Cardiac output = stroke volume x heart rate Can change frequency of contraction - chronotropy Can change force of contraction - inotropy  
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Regulation of Chronotropy - Increased heart rate   show
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Regulation of Chronotropy - Decreased heart rate   show
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Regulation of inotropy - hormones   show
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show Starling's law states that as length of the myocyte increases, force generated increases Steep change in tension depends on: change in double actin overlap and length dependant change in TpnC Ca affinity More blood in chambers more forceful contraction  
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