Gastrointestinal Sphincters: Anatomy, Function, and Clinical Relevance

Esophageal Sphincters

• Upper Esophageal Sphincter (UES): Cricopharyngeus muscle. Prevents air entry into esophagus, prevents reflux into pharynx.
• Lower Esophageal Sphincter (LES): Functional sphincter at gastroesophageal junction. Prevents gastric reflux. Incompetence → GERD.

Gastric Sphincter

• Pyloric Sphincter: Regulates gastric emptying into duodenum. Prevents bile reflux.

Small Intestinal Sphincters

• Sphincter of Oddi: Controls flow of bile and pancreatic juice into duodenum. Dysfunction → biliary pain, pancreatitis.
• Ileocecal Valve: Regulates ileal content entry into cecum; prevents colonic reflux.

Colonic/Anorectal Sphincters

• Internal Anal Sphincter (IAS): Smooth muscle, involuntary, maintains resting tone (85% of continence).
• External Anal Sphincter (EAS): Striated muscle, voluntary, provides urge control.
• Puborectalis muscle: Creates anorectal angle (key for continence).

Clinical Pearls

• LES dysfunction → GERD, Barrett's esophagus.
• Pyloric stenosis (infantile hypertrophy) → projectile vomiting.
• Sphincter of Oddi dysfunction → biliary-type pain post-cholecystectomy.
• IAS/EAS injury (trauma, childbirth, surgery) → fecal incontinence.