Potassium Balance

Question	Answer
In which foods can potassium be found?	Leafy vegetables, most fruit and fruit juice, potatoes
Where is concentration of potassium highest, intra or extra cellularly?	Intracellularly
What is meant by acute regulation of K+?	The distribution of K+ between intracellular and extracellular compartments.
What is meant by chronic regulation of K+?	The kidneys adjusting excretion and reabsorption of K+.
What are the 3 functions of K+?	1. Determines the osmolality of intracellular fluid and therefore also the fluid volume 2. Determines RMP 3. Affects vascular resistance
How is the intracellular K+ mostly maintained?	By Na+/K+ ATPase pumps in the membranes of cells.
Name 3 hormones that help regulate K+.	1. Insulin 2. Aldosterone 3. Adrenaline
Which equation is used to calculate the membrane potential based on intra and extra cellular concentrations of an ion?	The Nernst Equation
What is the boundary for hyperkalaemia?	plasma concentration K+ > 5.5mM
What is the boundary for hypokalaemia?	Plasma concentration K+ < 3.5mM
What is particularly affected by changes in plasma K+ concentration?	Firing of action potentials
How is this changed in hyperkalaemia?	There is easier depolarisation as RMP is less negative, so it is easier to reach threshold.
How is it changed in hypokalaemia?	Membranes are harder to depolarise, as RMP is more negative and therefore further away from threshold (hyperpolarised).
Where can this be particularly dangerous?	In cardiac tissue, as the depolarisation/repolarisation pattern in the membrane potentials is what gives the normal cardiac rhythm on an ECG.
What can cause hypokalaemia? (4)	1. Long-term use of diuretics without KCl compensation 2. Hyperaldosteronism 3. Prolonged vomiting causing Na+ loss and therefore aldosterone causing K+ excretion 4. Profuse diarrhoea
What is the hormonal effect of hypokalaemia?	Decreased release of insulin, aldosterone and adrenaline
What causes hyperkalaemia? (3)	1. Insufficient renal excretion 2. Increased release from damaged cells (chemotherapy, prolonged exercise, severe burns etc.) 3. Addison's disease
When does hyperkalaemia become particularly dangerous?	Plasma K+ concentration > 7mM causes asystolic cardiac arrest
What can be given to stimulate K+ influx back into cells in this case?	Insulin to stimulate Na+/K+ ATP ase pumps
What should also be given and why?	Glucose to prevent hypoglycaemia
In treatments for CVD, what are the associated risks?	1. Risk of hyperkalaemia when drugs such as beta blockers and ACE inhibitors are used (decrease activity of Na+/K+ ATPase pumps, prevent secretion of aldosterone) 2. Risk of hypokalaemia when loop diuretics used (increases K+ excretion)
In the kidneys, ___ and ____ are filtered freely, then ___________. The ________ of this in the __ __ __ is always more or less constant.	Na+ and K+, reabsorbed, fraction, PCT
What mechanisms allow K+ transport in the PCT? (3)	1. Na+/K+ ATPase pumps in the basolateral membrane, 2. K+ channels in the basolateral membrane, 3. Passive flow paracellularly between tight junctions.
What mechanisms allow transport of K+ in the thick ascending limb of the Loop of Henle? (3)	1. Na+/K+ ATPase pumps on the basolateral surface 2. K+ channels on the basolateral surface 3. Na+/K+ symporter on the apical surface
What mechanisms allow transport of K+ in the DCT? (3)	1. Na+/K+ ATPase pumps on the basolateral surface 2. K+ channels on both the basolateral and the apical surfaces 3. Possibly a Cl-/K+ symporter on the apical surface
How is secretion of K+ back into the tubule encouraged in the DCT?	ENaCs (epithelial Na+ channels) cause influx of Na+ so encourage efflux of K+ through K+ channels on the apical surface.
What are the effects of aldosterone on K+ secretion?	1. Increases activity of Na+/K+ ATPase pumps (intracellular concentration of K+ rises so increases concentration gradient) 2. Increases number of ENaCs so increases electrochemical gradient 3. Increases permeability of the apical membrane to K+
What stimulates secretion of aldosterone?	Increased plasma concentration of K+
What else can enhance K+ secretion?	Faster flow rate in the tubular lumen, as this removes the K+ more quickly and maintains a high concentration gradient.
What is thought to be the mechanism in place in severe hypokalaemia?	Reabsorption of K+ by the alpha-intercalated cells of the collecting ducts by a K+/H+ ATP antiporter.
What effect does the plasma pH have on K+?	In alkalosis, Na+/K+ATPase pumps work faster so can lead to hypokalaemia. In acidosis, these pumps slow down so K+ shifts to extracellular compartment and leads to hyperkalaemia.
How does Addison's disease cause imbalance of Na+/K+?	Deficiency of aldosterone, so K+ shifts out of cells (resulting in hyperkalaemia)
What is Conn's syndrome?	Hyperaldosteronism due to adenoma in adrenal cortex secreting aldosterone uncontrollably.
How does this disrupt K+ balance?	Too much aldosterone causes increased Na+ reabsorption and K+ excretion, resulting in hypokalaemia and hypernatraemia (leading to hypertension).

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	Created by Hannah Tribe about 10 years ago