Lumen of intestine, jejunum
Cross-sectional illustration of the intestinal lumen, here of the jejunum. The layers (from inside to outside) are called mucosa, submucosa, muscularis (muscular layer with longitudinal and circular orientation) as well as adventitia and serosa (layer of connective tissue and peritoneum). A characteristic of the intestinal mucosa are the macroscopic and microscopic plications, which highly increase the surface for resorption of water and nutrients.
