The surface of the duodenum is folded. These folds are known as plicae circulares (circular folds). However, there is a gradual decease in the diameter, thickness of the wall and number of folds, with distance from the duodenum. The folds are virtually absent in the terminal portion of the ileum. The mucosa of the small intestine is covered with tiny projections, known as villi. These villi become less numerous, smaller and more finger-like with distance from the duodenum. Numerous lymphatic nodes, called Peyer’s patches, are present in the mucosa and submucosa in the ileum. These are circular, aggregated lymph nodes that participate in the body’s immune response and synthesise antibodies.