ABSTRACT
The intestine is a tubelike structure that progresses from the duodenum to the rectum via the jejunum, ileum, ascending colon, transverse colon, and descending colon. The walls of the small intestine have several folds and are lined with millions of tiny fingerlike projections called villi. There are about 20 to 40 villi per square millimeter of mucosa, and each villus is about 0.5 to 1 mm long. The villus is covered by a single layer of columnar epithelium. The free edges of the cells of the epithelium of the villi are divided into minute microvilli, which form a brush border. The villi, microvilli, and the folds of the small intestine collectively increase the absorption surface about 600-fold.
