In humans, soluble wastes are excreted primarily by the urinary system and, to a lesser extent in terms of urea removed, by perspiration. The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The system produces urine by a process of filtration, reabsorption, and tubular secretion.n the urine of a healthy individual the color comes primarily from the presence of urobilin. Urobilin in turn is a final waste product resulting from the breakdown of heme from hemoglobin during the destruction of aging blood cells.