Serosa of small intestine

The serosa of small intestine refers to its outermost layer that corresponds to the visceral peritoneum. It consists of a thin layer of mesothelium comprising simple squamous epithelium with a dedicated basement membrane. Underneath the serosa, there exists a thin layer of connective tissue called the subserosa, that connects the serosa with the underlying muscularis external. Some texts, consider the subserosa as a part of the serosal layer.

Serosa of duodenum, jejunum, and ileum

In the small intestine, the duodenum is an exception, as much of its second, third, and fourth parts are retroperitoneal and therefore covered by adventitia rather than serosa on their posterior surfaces. In contrast, the jejunum and ileum are completely invested by serosa because they are intraperitoneal and suspended by the mesentery.

Functions

• The serosa provides a smooth, lubricated surface that reduces friction between the small intestine and adjacent abdominal organs during peristalsis and other movements.

• It also serves as a pathway for blood vessels, lymphatics, and nerves entering through the mesentery.