小腸の解剖（肉眼・組織）

Macroscopic and microscopic anatomy (histology) of the small intestine

要旨

十二指腸・小腸粘膜は吸収上皮としての性格をもつ上皮細胞に被覆され，絨毛構造がみられる。十二指腸のVater乳頭には胆管・膵管が開口し，乳頭の内側は胆・膵管上皮が被覆する点で，十二指腸他部位とは異なっているため，乳頭部と非乳頭部では発生する腫瘍の形質も異なる。十二指腸には胃の幽門腺に類似する粘液腺であるBrunner腺が粘膜固有層，粘膜下層に存在している。Brunner腺が存在する部分では，再生時に胃腺窩上皮化生が起こることがあり，胃型形質をもつ腫瘍の発生母地となっている可能性がある。

　An overview of the normal histology of the duodenum and small intestine is provided. The mucosa of the small intestine, including the duodenum, is covered with epithelial cells that have the characteristics of an absorptive epithelium, and a villous structure can be seen. Bile and pancreatic ducts open into the papilla of Vater in the duodenum, and the inside of the papilla is covered with biliary and pancreatic duct epithelium, which is different from other parts of the duodenum. Therefore, the characteristics of tumors that occur in the papilla and those in non-papillary areas are also different. In the duodenum, Brunner’s glands, which are mucus glands similar to the pyloric glands of the stomach, are present in the lamina propria and submucosa. Gastric foveolar epithelial metaplasia may occur during regeneration in areas where Brunner’s glands exist, and may serve as an origin for tumors with gastric phenotypes. It is important to understand normal structures and their histology in order to achieve appropriate recognition of endoscopic findings.