Heart burn - Oesophagitis - GERD - Metaplasia - Barretts - Carcinoma all progress from the failure of the LES (LOS-uk) to discharge it's function of preventing caustic chemicals migrating up from the stomach into the gullet.
This simplified flow diagram depicts cause and effect.
To understand this diagram it is necessary to remember that many systems in the body operate on a push/pull basis; that is one set of nerves supplies impulses causing an increase whilst an opposing set of nerves supplies impulses causing a decrease. The normal situation is where these stimuli are in the correct balance.
When, for myriad reasons, this balance is upset by an excess of or a deficiency in either or both of these driving forces then a disease process may be initiated.