ASCRS Ch02 — Colonic Physiology

Citation: Ault GT, Beaty JS. "Colonic Physiology." In: Steele SR, et al. (eds.), The ASCRS Textbook of Colon and Rectal Surgery, 4th ed. Springer Nature Switzerland AG; 2022. pp. 29–39 (PDF pp. 45–56 of the combined textbook file). Source file: raw/ASCRS Textbook 4th Ed.pdf (full 1,198-page textbook; not split into per-chapter files — cite by page range within the single PDF).

Type: Specialty textbook chapter (reference/background, not primary literature).

Scope

Second chapter of the sequential full-textbook ingest (see ASCRS Ch01 - Anatomy and Embryology for the ingest's scope/plan). Covers colonic embryology (brief recap plus new anorectal-timing detail), colonic wall histology, secretory/absorptive epithelial physiology, colonic innervation, visceral pain pathways, colonic motility and its pharmacologic/neuromodulatory modulators, and the gut microbiome.

Key content

Full synthesis written into the new concept page Colonic Physiology rather than summarized twice here — see that page for colonic wall histology (epithelial cell types, ICC, myenteric/submucosal plexuses), ion-transport mechanisms (sodium/potassium/aldosterone/CFTR, proximal vs. distal colon), SCFA and vitamin K absorption, innervation (extrinsic sympathetic/parasympathetic, intrinsic enteric nervous system), visceral pain and its IBS relevance, motility (segmental vs. propagated contractions, tone, colonic/rectal motor complexes, defecation physiology including the rectoanal inhibitory reflex), a detailed pharmacology section on motility modulators (5-HT₃/5-HT₄ agents, opioids, lubiprostone, bile acids, laxative classes, sacral nerve stimulation), and gut microbiome composition/ disease associations. The chapter's brief embryology recap contributed one new detail — anal sphincter developmental timing (external ~week 10, internal ~week 12) — which was added directly to Colorectal Anatomy & Embryology's Embryology section rather than duplicated.

Limitations

• Textbook chapter, not primary literature — cited figures (e.g., microbiome percentages, drug efficacy claims) are as reported by the chapter's authors from their own literature review.
• The microbiome section's claim that Bacteroidetes abundance is higher in Crohn's disease conflicts with Crohn Disease's existing (Sabiston-sourced) claim of decreased Bacteroides/Firmicutes in CD dysbiosis — flagged as an unresolved discrepancy on Colonic Physiology rather than silently reconciled; likely reflects genuine heterogeneity across microbiome studies rather than an error in either textbook.

Relevance

Second entry in the ASCRS ingest. Creates Colonic Physiology, the physiologic companion to Colorectal Anatomy & Embryology — together these give the wiki full GI-tract physiology coverage from duodenum through anal canal (alongside the existing Small Intestine Anatomy & Physiology). Adds mechanistic depth to Constipation's medical-management section, flags a microbiome-direction discrepancy with Crohn Disease, and surfaces the rectoanal inhibitory reflex — a defecation- physiology topic not previously covered anywhere in the wiki.