Phase 1 · Understand the Body — Why the disease behaves the way it does.
The One-Line Truth
The whole disease in one chain
Everything on this page exists to explain this line.
GERD and peptic ulcer disease happen when stomach acid ends up in the wrong place — either splashing up into the esophagus (the food tube) or eating a hole in the stomach or duodenum (the first part of the small intestine).
The Stomach's Broken Security System
Imagine a nightclub with a bouncer (the LES) at the door and a VIP lounge inside (the stomach) with a special protective coating on the walls. Normally the bouncer keeps rowdy people (acid) from sneaking back out into the lobby (esophagus), and the VIP lounge walls are painted with a graffiti-proof sealant (mucus and bicarbonate) so the walls never get damaged. GERD happens when the bouncer gets tired and keeps letting people back out into the lobby without permission (weak LES relaxations), or when a fire escape pulls the bouncer out of position (hiatal hernia). Peptic ulcer disease happens when either a vandal (H. pylori) spray-paints over the protective coating to damage the walls directly, or when the maintenance crew (prostaglandin E₂) gets fired and stops applying the sealant, leaving bare drywall that acid eats right through. Either way, acid touches tissue it should never touch, and the damage spreads until something breaks completely — like a pipe bursting through the wall (perforation) or a pipe bleeding inside the walls (hemorrhage).
American College of Gastroenterology (ACG) GERD Guideline 2022 · American College of Gastroenterology (ACG) Peptic Ulcer Disease Guideline 2017 · American Gastroenterological Association (AGA) · Cochrane Reviews on Helicobacter pylori and peptic ulcer · reviewed 2026-07-07