Large Intestine

The most important function of the large intestine is the absorption of water. Although the lining is folded, there are no villi and many fewer microvilli. On the lumen side of the gut wall note the purple projections. These are folds of the mucosa layer and are lined with many goblet cells (visible but not labeled in the mid and high magnification images) that produce mucus. This section has been made from a portion of large intestine near the rectum. When the fecal material reaches this site, most of the water has been extracted from it and the dehydrated pellets are being formed. Mucus is needed in large quantities to lubricate the intestine and help form pellets. If one examined a section close to the small intestine, the walls of the gut would be much more smooth. In the high magnification image, notice that the epithelial layer of the mucosa is simple columnar, as it is in most of the large intestine.  However, in the anal canal, the epithelial layer is stratified squamous to resist abrasion.

Beneath the purple staining mucosa layer is the muscularis mucosa, and then the submucosa.  In the muscularis layer, the muscularis externa appears very simple in this part of the large intestine. Only the circular muscle is complete with the longitudinal layer appearing as bands.  External to the muscularis externa is the serosa (not visible).

This section is specially prepared so that the goblet cells are prominent. They are labeled in the high magnification view.  Goblet cells are scattered among the columnar epithelial cells of the intestinal lining. The goblet cells, as their name implies, are "goblet-shaped." These cells secrete copious amounts of mucous to lubricate and further liquify the chyme.