Dr. Matt and Dr. Mike's Medical Podcast Defaecation | Physiology of Pooping
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Feb 21, 2026 A lively dive into the anatomy and reflexes that keep you continent and let you go when you find a toilet. Learn how the puborectalis sling, internal and external sphincters, and enteric neurotransmitters coordinate storage and expulsion. Hear about spinal cord effects, toilet training, holding strategies, and how stress or exercise can suddenly change bowel behavior.
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Puborectalis Creates A Protective Kink
- The puborectalis forms a sling creating a 90° anorectal angle that helps keep stool in until appropriate.
- Relaxing this sling (and sitting/squatting) straightens the angle to allow defecation.
Two Sphincters, Two Controls
- Internal anal sphincter is smooth muscle and works subconsciously while external sphincter is skeletal and under conscious control.
- Effective defecation requires rectal contraction, internal sphincter relaxation, and conscious external sphincter relaxation.
Basal Phase Does Unconscious Sampling
- Basal phase samples rectal contents about seven times per hour via small relaxations of the internal sphincter.
- This sampling uses visceral mechanoreceptors to assess stretch without conscious awareness.
