What is the expanded region of the lower rectum, where fecal matter is retained, known as?

Ampulla. The ampulla is an expanded part of the lower rectum that stores feces. The transverse rectal folds are three folds in the ampulla which help to support fecal mass, but they are not the same as the actual region that stores the feces. Anal columns are longitudinal folds of mucosa over rectal vessels. They are found on the inner wall of the anal canal. Anal valves are folds of mucosa that join the anal columns at their inferior ends and create spaces between the wall and the valves known as anal sinuses.