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The jejunum (〔''OED'' 2nd edition, 1989.〕〔(Entry "jejunum" ) in ''(Merriam-Webster Online Dictionary )''.〕) is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. The jejunum lies between the duodenum and the ileum. The jejunum is considered to begin at the attachment of the suspensory muscle of the duodenum to the duodenum, a location called the duodenojejunal flexure.〔 The division between the jejunum and ileum is not anatomically distinct. In adult humans, the small intestine is usually between 6-7m long, about two fifths of which (2.5 m) is the jejunum. ==Structure== The interior surface of the jejunum—which is exposed to ingested food—is covered in finger like projections of mucosa, called villi, which increase the surface area of tissue available to absorb nutrients from ingested foodstuffs. The epithelial cells which line these villi have microvilli. The transport of nutrients across epithelial cells through the jejunum and ileum includes the passive transport of sugar fructose and the active transport of amino acids, small peptides, vitamins, and most glucose. The villi in the jejunum are much longer than in the duodenum or ileum. The pH in the jejunum is usually between 7 and 9 (neutral or slightly alkaline). The jejunum and the ileum are suspended by mesentery which gives the bowel great mobility within the abdomen. It also contains circular and longitudinal smooth muscle which helps to move food along by a process known as peristalsis. If the jejunum is impacted by blunt force the emesis reflex (vomiting) will be initiated. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「jejunum」の詳細全文を読む スポンサード リンク
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