Chronic renal failure is a gradual and progressive loss of the ability of the kidneys to function normally. The change is irreversible and is due to loss of nephrons of the kidney. The nephrons are basic functioning unit of the kidney and there are normally about one million nephrons in each kidney.
The kidney is no longer able to clean toxins & waste product from blood and concentrate the urine . When patients begin to experience symptoms of kidney failure, most of their kidney function is lost. Simply it can be interpreted as kidneys gradually stopping to working.