Cell types of the epithelium
The epithelium consists of different cell types. The most abundant cells are enterocytes, which are also called intestinal absorptive cells, because their apical membrane and glycocalix is packed with digestive enzymes and transporters. The enterocytes are not only responsible for nutrient absorption, they also play an important role in processing antigens and presenting them to T cells.
The brush cells are another type of epithelial cells with microvilli on the apical side. Although brush cells have longer microvilli, they have a thinner glycocalix than enterocytes. The function of brush cells is still under investigation, but it was hypothesized that they have a receptor role.
Goblet cells are easily distinguished from the other two types. Goblet cells produce and secrete mucus into the lumen of the small intestine. Mucus is mainly composed of mucin glycoproteins, which form a gel-like layer covering the epithelial cells. This helps to protect the cells from physical damage by acting as a lubricant and the gel-like web of macromolecules also forms a barrier against bacteria cells. 
To further increase the absorptive surface of the small intestine, the epithelial cells are arranged in finger-like structures extending into the lumen. These so called villi (villus, singular) should not be confused with the microscopic cell extensions called microvilli. Villi can be several millimeters in length and consist of thousands of cells. The villi are kept in shape by the lamina propria; a loose web of connective tissue. It mainly consists of extracellular macromolecules, such as proteoglycan, polysaccharides, and collagen. This network of fibers is intercepted by blood and lymph vessels, which carry away the absorbed nutrients.