How is the small intestine attached to the posterior abdominal wall?

The small intestine is attached to the posterior abdominal wall by a structure known as the mesentery. The mesentery is a double layer of peritoneum that not only anchors the small intestine in place but also contains blood vessels, nerves, and lymphatics that supply the intestines. This connection allows for stability while still enabling the movement and expansion of the intestines during digestion.

In contrast, the peritoneum is a serous membrane that lines the abdominal cavity and covers the abdominal organs; it does not specifically attach the small intestine to the posterior abdominal wall. The falciform ligament is a fold of peritoneum that connects the liver to the anterior abdominal wall and does not play a role in attaching the small intestine. Similarly, the lesser omentum is another fold of peritoneum that connects the liver to the stomach and the first part of the duodenum, but it does not involve the attachment of the small intestine to the abdominal wall. Thus, the mesentery is the correct and specific answer for how the small intestine is supported in the abdominal cavity.