Rectum Function: Storage Organ, Not Digestion

The rectum is the final 12–15 cm of the large intestine. Its primary role is temporary storage of feces until defecation is socially appropriate.

What the Rectum Does NOT Do

• No mechanical digestion: No churning or segmentation (occurs in stomach/small intestine)
• No chemical digestion: No enzyme secretion (completed in small intestine)
• Minimal absorption: Only some water, electrolytes, and certain drugs (suppositories)

Key Functions

• Reservoir: Accommodates 300–500 mL of stool via compliant walls
• Sensory Signaling: Stretch receptors detect distension → urge to defecate
• Continence Maintenance: Internal/external anal sphincters + puborectalis muscle maintain closure
• Defecation Coordination: Rectal contraction + sphincter relaxation + abdominal straining (Valsalva)

Clinical Relevance

Rectal pathology (cancer, prolapse, fissures, radiation proctitis) disrupts storage and continence. Understanding its true function guides surgical decisions (e.g., sphincter preservation in low rectal cancer).