Which statement accurately describes sodium?

The statement that sodium is a major extracellular cation controlled by the kidneys is accurate. Sodium is primarily found in the extracellular fluid and plays a crucial role in maintaining fluid balance and osmotic pressure in the body. It is essential for various physiological processes, including nerve transmission and muscle contraction.

The kidneys regulate sodium levels in the body through processes such as filtration, reabsorption, and excretion. When sodium intake is high, the kidneys can excrete excess sodium to maintain homeostasis. Conversely, when intake is low, they can conserve sodium to ensure adequate levels in the bloodstream. This regulatory mechanism is vital for maintaining blood pressure and overall fluid balance.

In contrast, sodium is not a major intracellular cation (which is primarily potassium) nor an anion. Furthermore, stating that it has no significant role in fluid balance is misleading, as sodium's primary function is indeed in the control of extracellular fluid volume and osmotic pressure, critical factors in fluid balance.