Urea is a nitrogenous waste product generated in the liver via the detoxification of ammonia from protein and amino acid metabolism. It circulates in the bloodstream, is filtered by renal glomeruli, and is largely excreted in urine, with a minor fraction lost through sweat. In the kidney, urea contributes to the medullary osmotic gradient essential for urine concentration. As the primary non-toxic vehicle for nitrogen excretion, it prevents ammonia accumulation that could otherwise damage tissues. Impaired renal function reduces urea filtration efficiency, resulting in elevated blood urea nitrogen levels and retention of metabolic wastes.