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[[Category:Lizard_and_Snake_Glossary]]
==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.
==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|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|aldosterone]]
==Cellular Translocation==
* Vital for rapid control of potassium loads
* Helps control plasma concentration
* Moves potassium into the cell
* Stores potassium in skeletal muscle and liver
* Balances ECF and ICF
* Controlled by insulin and beta2 adrenoreceptors
** 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
* 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%)
* This results in there only being 10% of the original amount left in the [[Reabsorption and Secretion Along the Distal Tubule and Collecting Duct - Anatomy & Physiology#Distal Tubule|distal tubule]]
* However net reabsorption / secretion of potassium occurs in the distal tubule and first part of collecting duct
** Depends on bodies need
* Under the influence of [[Aldosterone|aldosterone]]
* This is where the amount of potassium excreted is determined
* Reabsorption occurs in the final part of the collecting duct
==Potassium and Aldosterone==
* [[Aldosterone]] is the most important regulator of potassium
* It causes increased secretion of potassium
* Increased potassium directly stimulates [[Aldosterone]] secretion
* Increases the activity and number of Na<sup>+</sup> / K<sup>+</sup> ATPase in basolateral membranes of the principal cells in the collecting duct and distal tubule
* Potassium moves into the cells and is then excreted down an electro-chemical gradient
==Factors Influencing Potassium Excretion==
1.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
2.Potassium: High potassium = increased potassium excretion which triggers the release of aldosterone.
[[Category:Electrolytes]]
[[Category:Minerals]]