27.35 : Histology of the Large Intestine

The large intestine, a vital component of the gastrointestinal tract, is structured with four main layers: the mucosa, submucosa, muscularis, and serosa. Each layer performs a distinct role in facilitating the smooth functioning of the large intestine.

The innermost mucosa layer comprises simple columnar epithelium, lamina propria, and muscularis mucosae. This layer is primarily populated with absorptive cells, tasked with water absorption, and goblet cells, responsible for secreting mucus to lubricate the passage of colonic contents. These cells are housed within tubular structures known as intestinal glands or crypts of Lieberkühn. Also present in the lamina propria are solitary lymphatic nodules that can extend into the submucosa.

The submucosa, made of areolar connective tissue, provides support and elasticity. The muscularis layer is characterized by an external longitudinal smooth muscle layer and an internal layer of circular smooth muscle. In the large intestine, sections of the longitudinal muscles thicken into three bands, known as teniae coli. These bands, through their tonic contractions, gather the colon into a series of pouches called haustra, giving the colon its distinctive puckered appearance.

The outermost layer, the serosa, is part of the visceral peritoneum. Small pouches of this peritoneum, filled with fat and attached to the teniae coli, are known as omental or epiploic appendices.