Regulates the distribution of potassium in the body

2021-05-05 09:56 AM

Absorption of potassium in a meal rich in vegetables and fruits to a volume of extracellular fluid will increase plasma potassium levels, most of the potassium ingested will rapidly migrate into cells until the kidneys can. Eliminate excess amount.

After eating a normal meal, the concentration of potassium in the extracellular fluid rises to a lethal level if ingested potassium does not migrate rapidly into cells.

For example, absorbing 40 mEq of potassium (the amount found in a meal rich in vegetables and fruit) to an extracellular volume of 14 litters increases plasma potassium levels by about 2.9 mEq / L if all Potassium remains in the extracellular compartment. Fortunately, most of the potassium ingested will quickly migrate into cells until the kidneys can remove the excess.

Insulin stimulates the absorption of potassium into cells

Insulin is important for increasing the ability of cells to absorb potassium after a meal. In people with insulin deficiency due to diabetes, the increase in plasma potassium levels after eating a meal is much greater than normal. However, insulin injections can help correct hyperkalaemia.

Aldosterone increases the absorption of potassium into cells

Increasing potassium intake also stimulates aldosterone secretion, increasing cellular absorption of potassium. Excess aldosterone secretion (Conn's syndrome) is almost always associated with hypokalaemia, partly due to the migration of extracellular potassium into cells. In contrast, patients with aldosterone production deficiency (Addison's disease) often experience clinically significant hyperkalaemia due to the accumulation of potassium in the extracellular space, as well as the kidneys that retain potassium.

Β-Adrenergic stimulation increases the ability of the cell to absorb potassium

Increased secretion of catecholamines, especially epinephrine, can induce the movement of potassium from the extracellular matrix into the intracellular fluid, primarily by activating β2-adrenergic receptors. In contrast, treating high blood pressure with β-adrenergic receptor blockers, such as propranolol, causes potassium to move out of cells and induces a tendency to hyperkalaemia.

Figure. The amount of potassium is normal, the distribution of potassium in the body fluids and the amount of potassium leaving the body

Factors that change K + into cells (decrease extracellular [K +])

Factors that alter the K + out of the cell (increase the extracellular [K +])

Insulin

Lack of insulin (diabetes mellitus)

Aldosterone

Aldosterone deficiency (Addison's disease)

β-adrenergic stimulation

Β-adrenergic blockers

Alkalosis

Acidosis

 

Cell lysis

 

Heavy activity

 

Increases the concentration of extracellular fluid osmosis

 

Board. Factors that can alter potassium distribution between intracellular and extracellular fluids

Acid-base abnormalities can cause changes in potassium distribution

Metabolic acidosis increases extracellular potassium, partly due to the loss of potassium from the cells, while metabolic alkalosis lowers the concentration of potassium in the extracellular fluid. Although the mechanisms responsible for the effect of hydrogen ion concentration on potassium internal distribution are not well understood, the effect of increasing hydrogen ion concentration is to reduce the activity of the sodium-potassium adenosine pump. triphosphatase (ATPase). This decrease in turn reduces the cellular uptake of potassium and increases the extracellular potassium concentration.

Cell lysis increases extracellular potassium concentration

When the cell is destroyed, a large amount of potassium contained in the cell is released into the extracellular space. This release of potassium can cause significant hyperkalaemia if a large amount of tissue is destroyed, as occurs with severe muscle trauma or during erythrocyte lysis.

Strenuous exercise can cause hyperkalaemia by releasing potassium from skeletal muscle

During prolonged exercise, potassium is released from skeletal muscle into the extracellular fluid. Usually, hyperkalaemia is mild, but it can have clinical significance after heavy exercise, especially in patients treated with β-adrenergic blockers or in people with insulin deficiency. In rare cases, hyperkalaemia after exercise can be severe enough to cause heart toxicity.

Increased permeability of extracellular fluid induces redistribution of potassium from the cell into the extracellular fluid

Increased permeability of the extracellular fluid causes the osmolality of fluid out of cells. Cell dehydration increases intracellular potassium concentration, thereby promoting the diffusion of potassium outside the cell and increasing the concentration of potassium in the extracellular fluid. Reducing extracellular fluid permeability has the opposite effect.

 

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