Small and large intestines of a man. The small intestine is responsible for the majority of nutrient absorption while the large intestine absorbs most of the remaining water and vitamins produced by the resident bacterial flora, as well as moving the waste material to its final destination in the rectum. The lower gastrointestinal tract sits slightly lower and wider in the female than in the male, due to the larger pelvic girdle of the female skeleton as adapted for childbirth.