Duodenum lining. Light micrograph of a section through the lining of the duodenum, the uppermost part of the small intestine. The lining is folded into numerous villi (purple/blue). These increase the surface area for the digestion of food. Underlying this layer is the muscularis mucosae (pink band, top left to lower centre). Beneath this is a layer of Brunner's glands (irregular and pale). These glands secrete an alkaline mucus which helps to protect the small intestine from stomach acids when food is passed to it from the stomach. Magnification: x50 at 35mm size.