Final answer:
Na+ is the major extracellular cation, important for osmotic pressure, hydration, and electrical neutrality of body fluids. Chloride is the major extracellular anion balancing the cations. The kidneys regulate sodium levels in the body.
Step-by-step explanation:
Na+ is the major extracellular cation; it is responsible for one-half of the osmotic pressure gradient that exists between the interior of cells, known as the intracellular fluid (ICF), and their surrounding environment, known as the extracellular fluid (ECF).
The importance of sodium in the body is underscored by its role in maintaining proper hydration, nerve function, and muscle function. While chloride is the predominant extracellular anion, and functions to balance cations in the ECF, maintaining the electrical neutrality of this fluid. Excess sodium intake, typical in a Western diet high in NaCl, can lead to hypertension, with the kidneys playing a crucial role in sodium excretion.