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==Potassium==
==Introduction==
Potassium is carefully regulated in the body - the consequences of altered Potassium levels are significant, including:
*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.
*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.
===Importance of Regulation===
==Sources of Potassium==
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.
==Methods of Control==
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:
#Cellular translocation
This is the main method of control; it is an acute response that triggers Potassium movement either into or out of the cells.
#Renal excretion
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]]
#GI excretion
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]].
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:
==Cellular Translocation==
* Vital for rapid control of potassium loads
* Vital for rapid control of potassium loads
* Helps control plasma concentration
* Helps control plasma concentration
** 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
==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%)
* Reabsorption occurs in the final part of the collecting duct
* Reabsorption occurs in the final part of the collecting duct
==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
* 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
==Factors Influencing Potassium Excretion==
#Sodium: High sodium = increased potassium excretion and:
* More sodium into cells
* Increased Na<sup>+</sup> / K<sup>+</sup> ATPase
* Pumps sodium into peritubular renal interstitium
* The resulting increased cellular uptake of potassium results in it moving down the electrochemical gradient into the nephron
#Potassium: High potassium = increased potassium excretion which triggers the release of aldosterone.
[[Category:Electrolytes]]
[[Category:Electrolytes]]
[[Category:Lizard_and_Snake_Glossary]]
[[Category:Lizard_and_Snake_Glossary]]
[[Potassium - Reptiles]]
[[Potassium - Reptiles]]