The small intestines consist of the duodenum, jejunum and ileum. This post contains many high yield images that help to identify some of the identifying features of the small intestine. Namely, the presence of microvilli and villi on the mucosal surface increase the surface area present for absorption within the GI tract. In addition to absorptive properties, the small intestines contain a muscular layer to aid in peristalsis (food digestion) and an outer serosal layer for added protection.
Several cell types are encountered in the small and large intestines. Goblet cells and Paneth cells are important landmarks of the intestinal tract. The presence or absence of these (or other cells such as inflammatory cells) can signify an underlying problem depending on the location within the GIT. It is important to know which portions of the GIT the presence of a certain cell type is considered "acceptable" versus indicating something "bad".