Difference between revisions of "Potassium"

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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).
 
  
==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.
  
====Decreased Extracellular Potassium====
+
==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:
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.
+
#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.
====Increased Extracellular Potassium====
+
#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]]
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.
+
#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]].
===Sources===
 
 
 
* Potassium is absorbed via passive diffusion from the [[Small Intestine Overview - Anatomy & Physiology|small intestine]]
 
* Also via active transport from the [[Colon - Anatomy & Physiology|colon]]
 
** Affected by [[Aldosterone]]
 
* Highly efficient
 
* It's recovered from cellular breakdown
 
** Haemolysis
 
** 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=====
 
*Potassium is moved either into or out of the cells  
 
*Acute response
 
* Main method of control
 
 
 
=====Renal excretion=====
 
* Makes up 90% of the chronic response
 
* Takes 4-6 hours to respond
 
* Allows fine control
 
* Influenced by [[Aldosterone|Aldosterone]]
 
 
 
=====GI excretion=====
 
* Makes up the other 10% of the chronic response
 
* Also influenced by [[Aldosterone]]
 
* Most important in renal failure
 
 
 
===Cellular Translocation===
 
  
 +
==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
  
===Renal Control===
+
==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
  
===Potassium and Aldosterone===
+
==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
  
===Factors Influencing Potassium Excretion===
+
==Factors Influencing Potassium Excretion==
====Sodium====
+
#Sodium: High sodium = increased potassium excretion and:
 
+
* More sodium into cells  
* High sodium = increased potassium excretion
+
* Increased Na<sup>+</sup> / K<sup>+</sup> ATPase
** More sodium into cells  
+
* Pumps sodium into peritubular renal interstitium
** Increased Na<sup>+</sup> / K<sup>+</sup> ATPase
+
* The resulting increased cellular uptake of potassium results in it moving down the electrochemical gradient into the nephron
** Pumps sodium into peritubular renal interstitium
+
#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
 
 
 
====Potassium====
 
 
 
* High potassium = increased potassium excretion
 
* Triggers aldosterone
 
  
 
[[Category:Electrolytes]]
 
[[Category:Electrolytes]]
 
[[Category:Lizard_and_Snake_Glossary]]
 
[[Category:Lizard_and_Snake_Glossary]]
 
[[Potassium - Reptiles]]
 
[[Potassium - Reptiles]]

Revision as of 21:01, 4 November 2010

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 and via active transport from the colon. It is regulated efficiently by Aldosterone levels and recovery from cellular breakdown during haemolysis or tissue damage.

Methods of Control

The K+ in the ECF only represents a very small amount of the total K+ in the body; however its concentration is maintained within very strict parameters. The homeostasis of K+ is managed by three routes:

  1. 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.

  1. 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

  1. 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.

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+ / K+ 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 proximal tubule (70%) and along the ascending limb of the Loop of Henle (10-20%)
  • This results in there only being 10% of the original amount left in the 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
  • 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+ / K+ 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+ / K+ 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
  1. Potassium: High potassium = increased potassium excretion which triggers the release of aldosterone.

Potassium - Reptiles