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The jejunum is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been previously digested by enzymes in the duodenum .
The jejunum is specialized for the absorption through its lining by enterocytes: small nutrient particles which have been previously digested by enzymes in the duodenum. The main function of the ileum is to absorb vitamin B 12, bile salts, and whatever products of digestion that were not absorbed by the jejunum.
From here it passes into the first of the three sections of the small intestine, the duodenum (the next section is the jejunum and the third is the ileum). The duodenum is the first and shortest section of the small intestine. It is a hollow, jointed C-shaped tube connecting the stomach to the jejunum.
The suspensory muscle attaches the superior border of the ascending duodenum to the jejunum. The suspensory muscle is an important anatomical landmark that shows the formal division between the duodenum and the jejunum, the first and second parts of the small intestine, respectively. [14]
Intestinal glands are found in the epithelia of the small intestine, namely the duodenum, jejunum, and ileum, and in the large intestine (colon), where they are sometimes called colonic crypts. Intestinal glands of the small intestine contain a base of replicating stem cells , Paneth cells of the innate immune system , and goblet cells , which ...
The chyme moves through the jejunum and the ileum, where digestion progresses, and the non-useful portion continues onward into the large intestine. The duodenum is protected by a thick layer of mucus and the neutralizing actions of the sodium bicarbonate and bile. At a pH of 7, the enzymes that were present from the stomach are no longer active.
Enteroendocrine cells are specialized cells of the gastrointestinal tract and pancreas with endocrine function. They produce gastrointestinal hormones or peptides in response to various stimuli and release them into the bloodstream for systemic effect, diffuse them as local messengers, or transmit them to the enteric nervous system to activate nervous responses.
This forms the beginning of the jejunum. [3] The duodenojejunal flexure is surrounded by the suspensory muscle of the duodenum. [4]: 274 It is retroperitoneal, so is less mobile than the jejunum that comes after it, helping to stabilise the jejunum. [5]