potassium

Last edited 02/2018 and last reviewed 08/2023

Potassium is the chemical element at number 19 in the periodic table, symbol K.

• it is the most abundant cation in the human body
• total body potassium in the adult male is approximately 3500 mmol
• about 3000 mmol is exchangeable. Only 50-60 mmol is present in the extracellular space
• 98% of total body potassium is in the intracellular fluid (concentration about 140 mmol/l) while a small proportion is in the extracellular compartment (3.8-5.0 mmol/l) (2)
• ratio of intracellular end extracellular potassium (Ki/Ke) is the most important factor which determine the resting membrane potential of cell membranes (1,2)

Potassium is excreted in urine (90%) and through the gastrointestinal tract (10%).

• normal food intake suffices daily requirements (80-120 mmol/day)
• if the diet is potassium free then the kidney still excretes 10-20 mmol of potassium per litre of urine (derived principally from distal tubule secretion).

In the gastrointestinal tract there is passive absorption of potassium in the proximal small bowel. Potassium is secreted (in exchange for sodium) in the colon. A gastric aspirate contains 10-15 mmol/l of potassium.

Disturbances in potassium regulation, and resultant changes in serum potassium concentration, may alter membrane excitability which affects the functions of nerve, muscle, and cardiac muscles (2).

Reference:

• (1) Rastegar A, Soleimani M. Hypokalaemia and hyperkalaemia. Postgrad Med J. 2001;77(914):759-64. 
• (2) Nyirenda MJ et al. Hyperkalaemia. BMJ. 2009;339:b4114.