四十四難曰：七衝門何在？ 然：唇為飛門，齒為戶門，會厭為吸門，胃為賁門，太倉下口為幽門，大腸小腸會為闌門，下極為魄門，故曰七衝門也。
用「闌」這個字找內經本文，沒有看到相關段落。「闌，門遮也。」在《說文》的本義是指門前的柵欄。根據大腸小腸會的提示，現代的生理專有名詞叫作「迴盲瓣」。
迴盲瓣（Ileocecal valve）是分隔大腸和小腸的括約肌。主要功能是避免大腸內的物質迴流進迴腸。每天約有二公升的流體會經過迴盲瓣進入大腸。(wiki)
ADAM有一個彩圖也還蠻清楚的：
Src: http://trihealth.adam.com/content.aspx?productid=10&pid=10&gid=000327
解剖學上的細節：
The ileocecal valve consists of two muscular layers of ileum, an upper and lower lip, that are covered by mucuosa and protrude into the lumen of the caecaum supported by mucosal folds called frenula. This forms the opening of the terminal ileum into the medial cecum and delineates the upper margin of the cecum from the ascending colon.
Ileocecal valve | Radiology Reference Article | Radiopaedia.org
在腹部的象限來說，屬於右下象限。
Right iliac fossa mass - Liberal Dictionary
英文的wiki上面補充，迴盲瓣是消化系統裡面唯一吸收Vit B12跟膽鹽的地方。
The ileocecal valve is distinctive because it is the only site in the gastrointestinal tract that is used for vitamin B12 and bile acid absorption