Small Intestine (Amphiuma)

This organ is the major site of digestion and absorption of nutrients (except water). Orient yourself by locating the central lumen. Note that the absorptive surface area is increased by three adaptations: 1) circular folds of the intestinal wall; 2) villi, finger-like projections into the lumen; and, 3) microvilli, which project from the surface of the epithelial cells lining the lumen. On this slide you should be able to see both the circular folds and the villi. The epithelial layer is columnar epithelium, which is specialized for absorption and secretion. The muscularis consists of an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle. The outermost layer is the serosa, or visceral peritoneum, which consists of an inner layer of connective tissue and an outer layer of mesothelium.