most digestion in the small intestine takes place in the jejunum.
most digestion in the small intestine takes place in the jejunum.
where does most digestion in the small intestine take place?
the jejunum
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.
intestinal bypass
as with other vertebrates, the intestines of fish consist of two segments, the small intestine and the large intestine. in most higher vertebrates, the small intestine is further divided into the duodenum and other parts. in fish, the divisions of the small intestine are not as clear, and the terms "anterior intestine" or "proximal intestine" may be used instead of duodenum. in bony fish, the intestine is relatively short, typically around one and a half times the length of the fish's body. it commonly has a number of "pyloric caeca", small pouch-like structures along its length that help to increase the overall surface area of the organ for digesting food. there is no ileocaecal valve in teleosts, with the boundary between the small intestine and the rectum being marked only by the end of the digestive epithelium. there is no small intestine as such in non-teleost fish, such as sharks, sturgeons, and lungfish. instead, the digestive part of the gut forms a "spiral intestine", connecting the stomach to the rectum. in this type of gut, the intestine itself is relatively straight, but has a long fold running along the inner surface in a spiral fashion, sometimes for dozens of turns. this fold creates a valve-like structure that greatly increases both the surface area and the effective length of the intestine. the lining of the spiral intestine is similar to that of the small intestine in teleosts and non-mammalian tetrapods. in lampreys, the spiral valve is extremely small, possibly because their diet requires little digestion. hagfish have no spiral valve at all, with digestion occurring for almost the entire length of the intestine, which is not subdivided into different regions.
fish anatomy