Wall composition of the small intestine

The wall of the small intestine contains four layers of tissue found in the rest of the gastrointestinal tract: mucosa, submucosa, muscularis, and serosa.

The structure of the wall has unique features that facilitate the process of digestion and absorption: circular folds, villi, and microvilli. Circular folds (plicae circulares) are folds of mucosa and submucosa. They stretch from the proximal portion of the duodenum and end at about the midportion of the ileum. They are crucial in the enhancement of absorption by increasing the surface area and causing static, spiral movement of the food matter.

The surface area of absorption is increased even further by the presence of villi and microvilli.

Figure 1: Three levels of complexity of the structure of the small intestine. The lining of the small intestine has circular folds, which are rich in villi. Each villus has absorptive cells that contain microvilli. All structures increase absorption surface area of the intestine.