Mucosa: Epithelium

The small intestine is lined by a simple columnar epithelium of absorptive cells (enterocytes with microvilli) and goblet cells. Microvilli, which form a brush border on the apical surface of the absorptive cells are shown in greater detail in the electron micrograph. 1000x, 25,000x

The small intestine is lined by a simple columnar epithelium of absorptive cells (enterocytes with microvilli) and goblet cells. Microvilli, which form a brush border on the apical surface of the absorptive cells are shown in greater detail in the electron micrograph. 1000x, 25,000x

The luminal surfaces of enterocytes are covered by microvilli that greatly increase the surface area for absorption. Each cells may have up to 1000 mcrovilli, collectively forming a brush border (striated border).

Extending from the microvilli is the glycocalyx, consisting of highly branched carbohydrate molecules that sequester enzymes important in digestion and in the transport of nutrients. The glycocalyx also aids in retention of the bacterial flora present in the intestinal lumen.

Goblet cells are the second cell type in the epithelium. Mucin droplets produced by these cells accumulate in the bulging apex, while the nucleus and remaining cytoplasm form the “stem” of each goblet. Goblet cells, found throughout the small and large intestines, produce mucus that lubricates the surface of the intestines.

Also present in the epithelium are wandering lymphocytes and macrophages that provide immune surveillance.

A lamina propria of loose connective tissue underlies the epithelium.