Cardiac Sphincter vs. Lower Esophageal Sphincter: Clarifying Reflux Prevention

Terminology

The terms cardiac sphincter and lower esophageal sphincter (LES) refer to the same functional unit — the high-pressure zone at the esophagogastric junction.

Function

• Primary role: Prevent reflux of gastric contents (acid, bile, pepsin) into the esophagus.
• Secondary: Permit antegrade bolus passage during swallowing (transient relaxation).
• Not a barrier to entry: Food enters stomach because the LES relaxes; it does not block entry.

Mechanism of Reflux (GERD)

• Inappropriate transient LES relaxations (TLESRs) — most common.
• Chronically low LES pressure (<10 mmHg).
• Hiatal hernia disrupts crural diaphragm contribution.
• Increased intra-abdominal pressure (obesity, pregnancy).

Clinical Pearl

The LES is a one-way valve (stomach → esophagus blocked; esophagus → stomach permitted via swallowing-induced relaxation). It does not prevent food entry — it facilitates it by coordinated relaxation.