How does one distinguish the large bowel from the small bowel?

The large bowel has plicae semilunaris (i.e., folds that extend part of the way across the lumen between the haustra). The large bowel may contain stool and usually frames the abdomen. It forms a “picture frame” for the abdomen.

The small bowel has valvulae conniventes (i.e., folds that extend all of the way across the lumen, also known as plicae circulares) except in the distal ileum. The small bowel is usually more central than the large bowel.