in the human digestive system, the stomach is responsible for mechanical and chemical digestions. the small intestine is involved in both the absorption and digestion of nutrients, whereas the large intestine is responsible for the elimination of wastes (defecation). the small intestine consists of 3 parts: duodenum, jejunum and ileum. the duodenum is the first part of the small intestine and is connected to the stomach via the pyloric valve. the jejunum is the second and middle part of the small intestine. the ileum is the last part of the small intestine and is connected to the cecum, a part of the large intestine, via the ileocecal valve.