frankiesunshine
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why does it decrease with acidosis?
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| MLF
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Acidosis means more potassium remember with potassium, H+ protons also accumulate resulting in acidosis and more potassium means less contractility of the heart like repolarization.
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| mildus
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Acidosis is when extracellular H+ is increased (extracellular pH is decreased ). If so, H+ will enter the cell in order to normalize extracellular pH. As H+ enters the cell, it pushes K+ towards the outside of cell (why? in order to maintain electrical neutrality in cell, because positive H has come into the cell, so positive K must leave the cell). As K+ leaves the cell, resting transmembrane potential increases (becomes more negative) so excitability is decreased.
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| ssrpk
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well i agree with u about the fact tht in order tio maintain cellular neutrality K+ goes out inc. its conc. in the ecf!
however hyperkalemia depolarizes the membrane! [decreases equilibrium potential of K+]
and likewise hypokalemia hyperpolarizes the membrane [inc. equilibrium potential of K+]
now, this sems like a paradox because we say tht hyperkalemia reduces automaticity while hypokalemia increases automaticity! [tht's a separate issue but this is how it goes]
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| mildus
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Hyperkalemia increases excitability, but when it triggers a single action potential, the refractory period is prolonged (repolarization fase is prolonged, due to decreased concentration gradient for potassium). The next action potential is more difficult to be triggered (due to prolonged rafractory period), so frequency decreases.
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