Which of the following is NOT a retroperitoneal organ?

The stomach is classified as an intraperitoneal organ, meaning it is located within the peritoneal cavity and is surrounded by visceral peritoneum. This anatomical position allows the stomach to have greater mobility and flexibility as it expands and contracts during digestion.

In contrast, both the kidneys and adrenal glands are retroperitoneal organs. They are situated outside the peritoneal cavity, lying against the posterior abdominal wall, and are covered by peritoneum only on their anterior surface. The bladder is also considered retroperitoneal, as it is located behind the peritoneum, resting on the pelvic floor. Thus, when identifying organs based on their anatomical positions relative to the peritoneal cavity, the stomach distinctly stands out as not being retroperitoneal.