Mucosa of small intestine
Tunica mucosa intestini tenuis
- Synonym: Mucous membrane of small intestine
- Related terms: Mucosa; Mucous membrane
Definition
The mucous membrane (tunica mucosa) is thick and highly vascular at the upper part of the small intestine, but somewhat paler and thinner below. It consists of the following structures: next the areolar or submucous coat is a double layer of unstriped muscular fibers, outer longitudinal and inner circular, the muscularis mucosæ internal to this is a quantity of retiform tissue, enclosing in its meshes lymph corpuscles, and in this the bloodvessels and nerves ramify; lastly, a basement membrane, supporting a single layer of epithelial cells, which throughout the intestine are columnar in character. The cells are granular in appearance, and each possesses a clear oval nucleus. At their superficial or unattached ends they present a distinct layer of highly refracting material, marked by vertical striæ, the striated border.