Which of the following is considered a primary extracellular electrolyte?

Sodium is considered a primary extracellular electrolyte because it plays a crucial role in maintaining fluid balance and is the predominant cation found in the extracellular fluid (ECF) compartment of the body. This electrolyte is vital for various physiological processes, including the regulation of blood pressure, transmission of nerve impulses, and muscle contraction.

The concentration of sodium in the extracellular fluid is significantly higher than that of other electrolytes, which facilitates the osmotic balance and the movement of water across cell membranes. In contrast, while potassium is more abundant in intracellular fluid, calcium, and magnesium have limited roles relative to sodium in extracellular fluid dynamics. Thus, sodium's key functions and its predominant presence in the ECF make it the primary extracellular electrolyte. This understanding is essential for grasping how electrolyte imbalances can impact overall bodily functions and health.