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Potassium is generally in the range of 2 to 8 mmol/l. Hypokalaemia in reptiles will occur from inadequate intake or excessive loss (diarrhoea). In mammals hyperkalaemia with excessive potassium intake, decresed secretion or shift from intracellular to extracellular fluid (e.g.severe acidosis).
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==Potassium==
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==Introduction==
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Potassium is carefully regulated in the body - the consequences of altered Potassium levels are significant, including:
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*reduced concentration of potassium in the ECF leads to plasma membranes hyperpolarization resulting in decreased firing of action potentials.  This causes skeletal muscle weakness and cardiac abnormalities.
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*increased concentration of potassium in the ECF leads to membrane depolarisation which is inappropriately triggered by action potentials.  This can make the membrane insensitive to further stimulation causing cardiac abnormalities.
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===Importance of Regulation===
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==Sources of Potassium==
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Potassium is absorbed via passive diffusion from the [[Small Intestine Overview - Anatomy & Physiology|small intestine]] and via active transport from the [[Colon - Anatomy & Physiology|colon]]. It is regulated efficiently by [[Aldosterone]] levels and recovery from cellular breakdown during haemolysis or tissue damage.
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====Decreased Extracellular Potassium====
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==Methods of Control==
 
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The K<sup>+</sup> in the ECF only represents a very small amount of the total K<sup>+</sup> in the body; however its concentration is maintained within very strict parameters.  The homeostasis of K<sup>+</sup> is managed by three routes:
If the concentration of potassium in the ECF is reduced then the plasma membranes hyperpolarize resulting in decreased firing of action potentials.  This causes skeletal muscle weakness and cardiac abnormalities.
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#Cellular translocation
 
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This is the main method of control; it is an acute response that triggers Potassium movement either into or out of the cells.
====Increased Extracellular Potassium====
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#Renal excretion
 
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This method makes up 90% of the chronic response (takes 4-6 hours to respond). It allows fine control and is regulated by [[Aldosterone|Aldosterone]]
In this state the membrane is depolarised and is inappropriately triggered by action potentials.  This can make the membrane insensitive to further stimulation causing cardiac abnormalities.
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#GI excretion
 
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This route makes up the other 10% of the chronic response and becomes significant in cases of renal failure. This response is also influenced by [[Aldosterone]].
===Sources===
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* Potassium is absorbed via passive diffusion from the [[Small Intestine Overview - Anatomy & Physiology|small intestine]]
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* Also via active transport from the [[Colon - Anatomy & Physiology|colon]]
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** Affected by [[Aldosterone]]
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* Highly efficient
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* It's recovered from cellular breakdown
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** Haemolysis
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** Tissue damage
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===Methods of Control===
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The K<sup>+</sup> in the ECF only represents a very small amount of the total K<sup>+</sup> in the body however its concentration is maintained within very strict parameters.  The homeostasis of K<sup>+</sup> is managed by three routes:
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=====Cellular translocation=====
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*Potassium is moved either into or out of the cells  
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*Acute response
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* Main method of control
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=====Renal excretion=====
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* Makes up 90% of the chronic response
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* Takes 4-6 hours to respond
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* Allows fine control
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* Influenced by [[Aldosterone|Aldosterone]]
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=====GI excretion=====
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* Makes up the other 10% of the chronic response
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* Also influenced by [[Aldosterone]]
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* Most important in renal failure
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===Cellular Translocation===
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==Cellular Translocation==
 
* Vital for rapid control of potassium loads
 
* Vital for rapid control of potassium loads
 
* Helps control plasma concentration
 
* Helps control plasma concentration
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** Increases the activity of Na<sup>+</sup> / K<sup>+</sup> ATPases causing sodium efflux and potassium influx
 
** Increases the activity of Na<sup>+</sup> / K<sup>+</sup> ATPases causing sodium efflux and potassium influx
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===Renal Control===
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==Renal Control==
 
* Potassium ions are reabsorbed and secreted at different points along the nephron
 
* Potassium ions are reabsorbed and secreted at different points along the nephron
 
* Active reabsorption of potassium occurs along the [[Reabsorption and Secretion Along the Proximal Tubule - Anatomy & Physiology|proximal tubule]] (70%) and along the ascending limb of the [[Reabsorption and Secretion Along the Loop of Henle - Anatomy & Physiology| Loop of Henle]] (10-20%)
 
* Active reabsorption of potassium occurs along the [[Reabsorption and Secretion Along the Proximal Tubule - Anatomy & Physiology|proximal tubule]] (70%) and along the ascending limb of the [[Reabsorption and Secretion Along the Loop of Henle - Anatomy & Physiology| Loop of Henle]] (10-20%)
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* Reabsorption occurs in the final part of the collecting duct
 
* Reabsorption occurs in the final part of the collecting duct
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===Potassium and Aldosterone===
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==Potassium and Aldosterone==
 
   
* [[Aldosterone]] is the most important regulator of potassium
 
* [[Aldosterone]] is the most important regulator of potassium
 
* It causes increased secretion of potassium
 
* It causes increased secretion of potassium
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* Potassium moves into the cells and is then excreted down an electro-chemical gradient
 
* Potassium moves into the cells and is then excreted down an electro-chemical gradient
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===Factors Influencing Potassium Excretion===
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==Factors Influencing Potassium Excretion==
====Sodium====
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#Sodium: High sodium = increased potassium excretion and:
 
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* More sodium into cells  
* High sodium = increased potassium excretion
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* Increased Na<sup>+</sup> / K<sup>+</sup> ATPase
** More sodium into cells  
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* Pumps sodium into peritubular renal interstitium
** Increased Na<sup>+</sup> / K<sup>+</sup> ATPase
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* The resulting increased cellular uptake of potassium results in it moving down the electrochemical gradient into the nephron
** Pumps sodium into peritubular renal interstitium
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#Potassium: High potassium = increased potassium excretion which triggers the release of aldosterone.
** The resulting increased cellular uptake of potassium results in it moving down the electrochemical gradient into the nephron
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====Potassium====
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* High potassium = increased potassium excretion
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* Triggers aldosterone
      
[[Category:Electrolytes]]
 
[[Category:Electrolytes]]
 
[[Category:Lizard_and_Snake_Glossary]]
 
[[Category:Lizard_and_Snake_Glossary]]
 
[[Potassium - Reptiles]]
 
[[Potassium - Reptiles]]
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