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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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| − | ==Introduction==
| + | [[Category:Lizard_and_Snake_Glossary]] |
| − | 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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| − | ==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|aldosterone]] levels and recovery from cellular breakdown during haemolysis or 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 - this is the main method of control; it is an acute response that triggers Potassium movement either into or out of the cells.
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| − | #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]]
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| − | #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]]
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| − | ==Cellular Translocation==
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| − | * Vital for rapid control of potassium loads
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| − | * Helps control plasma concentration
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| − | * Moves potassium into the cell
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| − | * Stores potassium in skeletal muscle and liver
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| − | * Balances ECF and ICF
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| − | * Controlled by insulin and beta2 adrenoreceptors
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| − | ** 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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| − | * Potassium ions are reabsorbed and secreted at different points along the nephron
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| − | * 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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| − | * 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]]
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| − | * However net reabsorption / secretion of potassium occurs in the distal tubule and first part of collecting duct
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| − | ** Depends on bodies need
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| − | * Under the influence of [[Aldosterone|aldosterone]]
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| − | * This is where the amount of potassium excreted is determined
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| − | * Reabsorption occurs in the final part of the collecting duct
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| − | ==Potassium and Aldosterone==
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| − | * [[Aldosterone]] is the most important regulator of potassium
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| − | * It causes increased secretion of potassium
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| − | * Increased potassium directly stimulates [[Aldosterone]] secretion
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| − | * 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
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| − | * 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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| − | 1.Sodium: High sodium = increased potassium excretion and:
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| − | * More sodium into cells
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| − | * Increased Na<sup>+</sup> / K<sup>+</sup> ATPase
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| − | * Pumps sodium into peritubular renal interstitium
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| − | * The resulting increased cellular uptake of potassium results in it moving down the electrochemical gradient into the nephron
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| − | 2.Potassium: High potassium = increased potassium excretion which triggers the release of aldosterone.
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| − | [[Category:Electrolytes]]
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| − | [[Category:Minerals]] | |