(1)Prerenal failure(functional RF or prerenal azotemia) caused by any disorder external to the kidneys that rapidly and severely decreases the blood supply to the nephron (2)Intrarenal failure(parenchymal RF) caused by disease of the renal tissue itself, affecting the blood vessels, glomeruli or tubules (3)Postrenal failure(Obstructive RF, Postrenal azotemia) caused by obstructive disorders(uretal or urethral) that can block or partially block urine flow, while the kidney's blood supply and other functions are initially normal 1818 caused by any disorder external to the kidneys that rapidly and severely decreases the blood supply to the nephron. caused by disease of the renal tissue itself, affecting the blood vessels, glomeruli or tubules. caused by obstructive disorders (uretal or urethral) that can block or partially block urine flow, while the kidney's blood supply and other functions are initially normal. ( l ) Prerenal failure (functional RF or prerenal azotemia) (2) Intrarenal failure (parenchymal RF) (3) Postrenal failure (Obstructive RF, Postrenal azotemia)