Rectum

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.

Normal rectum

Section of a normal rectum, stained with hematoxylin and eosin for contrast.

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Rectum

The rectum is histologically composed of three main structural layers:

  • Mucosa: Mucosal membrane, lining the inside of the intestine.
  • Submucosa: Connective tissue layer.
  • Muscularis externa: A layer of smooth muscle.