What is the most prevalent cation in extracellular fluid?

What is the most prevalent cation in extracellular fluid?

• A. Potassium
• B. Sodium
• C. Calcium
• D. Magnesium

Answer: (B)

In the extracellular fluid, the dominant positively charged ion is sodium. The concentration of sodium in the extracellular space is about 140 mEq/L, which largely sets the fluid’s osmolarity and drives water movement between compartments, influencing blood volume and pressure. Potassium, while essential, is mostly inside cells, with only a small amount in the extracellular fluid. Calcium and magnesium are present extracellularly as well, but their total extracellular cation levels are much lower than sodium’s. So, sodium is the most prevalent cation in extracellular fluid.

In the extracellular fluid, the dominant positively charged ion is sodium. The concentration of sodium in the extracellular space is about 140 mEq/L, which largely sets the fluid’s osmolarity and drives water movement between compartments, influencing blood volume and pressure. Potassium, while essential, is mostly inside cells, with only a small amount in the extracellular fluid. Calcium and magnesium are present extracellularly as well, but their total extracellular cation levels are much lower than sodium’s. So, sodium is the most prevalent cation in extracellular fluid.