Which is the principal system for regulation of fluid and electrolyte balance?

A) Cardiac
B) Vascular
C) Pulmonary
D) Renal

The renal system is responsible for regulating fluid and electrolyte balance in the body by controlling the amount of water and electrolytes that are excreted in the urine. It accomplishes this through processes such as reabsorption and secretion in the kidneys. The cardiac, vascular, and pulmonary systems are not primarily involved in regulating fluid and electrolyte balance.