What structure encloses most of the abdominal organs?

The structure that encloses most of the abdominal organs is the peritoneum. The peritoneum is a serous membrane that forms a protective sac within the abdominal cavity. It consists of two layers: the parietal peritoneum, which lines the abdominal wall, and the visceral peritoneum, which covers the abdominal organs. This arrangement not only protects the organs but also provides lubrication, allowing for the free movement of the organs during digestion and other activities.

The greater and lesser sacs are components of the peritoneal cavity that do help organize it but do not encompass the organs directly. The greater sac is the main part of the peritoneal cavity, while the lesser sac (also known as the omental bursa) is a smaller extension located posterior to the stomach. The mesentery is a fold of peritoneum that attaches the intestines to the abdominal wall but does not enclose the entire abdominal cavity. Thus, the peritoneum is the most comprehensive structure for enclosing abdominal organs.