Intestinal lining. Light micrograph of villi on the lining of the jejunum, part of the small intestine. The lining has many folds, known as plicae circulares or Kerckring's valves, in this region. Both the plicae and villi serve to increase the surface area for the absorption of nutrients from the gut lumen. The folds are mainly composed of columnar epithelial cells (purple) interspersed with goblet cells (pink). The goblet cells secrete mucous, which lines the surface of the membrane. Magnification: x60 when printed 10cm wide.