The rectum is approximately 20 cm long. It is continuous with the sigmoid colon and anal canal and functions as a reservoir for feces before excretion. Histologically, the rectum resembles the colon with straight tubular glands that extend through the thickness of the mucosa. The glands are almost entirely lined by mucous-secreting goblet cells but some scarce enterocytes are also seen.

There is more diffuse lymphoid tissue in the rectum than in the remainder of the large intestine and both plasma cells and occasional eosinophilic granulocytes are often present.