The mucosa consists of mucosal glands, crypts, and other stuff
intussusception
Lumen
lumanate its inside
It is the space within the intestine
small intestine
The word is lumen. It means the interior of a hollow tubular structure such as the intestine.
The lumen is the inner open space or cavity of a tubular organ, such as a blood vessel or an intestine
The small intestine has many villi, small projections into the lumen of the small intestine. These villi increase the surface area of the small intestine, and increase the funcitonal area for the absorbtion of nutrients.
Villi
It lines the lumen of the vessels, and is a thin layer of endothelium.
Villi
longitudinal muscle