Which organs are classified as retroperitoneal?

The classification of organs as retroperitoneal refers to their anatomical position in relation to the peritoneum, which is the serous membrane that lines the abdominal cavity. Retroperitoneal organs are located behind the peritoneum and include structures that are not entirely encased in peritoneum.

The correct answer identifies the duodenum, pancreas, and adrenal glands as retroperitoneal organs. The kidneys are also retroperitoneal; they are located at the back of the abdominal cavity, outside the peritoneum. The duodenum, as the first segment of the small intestine, is partially retroperitoneal because parts of it are fixed to the posterior abdominal wall. The pancreas lies horizontally across the back of the abdomen, predominantly in a retroperitoneal location. The adrenal glands, located on top of each kidney, are also situated posteriorly and are classified as retroperitoneal due to their anatomical relationship.

In contrast, the other options contain organs commonly found in the intraperitoneal cavity or have a different anatomical classification. For example, the liver, pancreas, and spleen listed in the first option are not all classified as retroperitoneal, as the liver is entirely intraperitoneal. In