Understanding the physiology of the upper gastrointestinal (GI) tract is crucial to ensuring effective reflux management. Here you can learn all you need to know about the physiology of the stomach, oesophagus and acid secretion, as well as the pathophysiology and complications of reflux.
Upper GI anatomy and physiology
The stomach and the oesophagus are part of the upper GI tract. The lower oesophageal sphincter is a circular smooth muscle layer that lies at the gastroesophageal junction.
Mechanisms to prevent reflux
- Lower oesophageal sphincter
Maintains a pressure at the gastroesophageal junction greater than the intragastric pressure.
- Crural diaphragm
Functions as an external sphincter, contributing towards the pressure at the gastroesophageal junction.
- Flap valve
Exists where the oesophagus enters the stomach, acting as a physical barrier to the retrograde flow of stomach contents.
|Cells||What do they secrete?||Function|
|Parietal cells||Hydrochloric acid (HCl)||Secreted into the stomach via proton pumps, acid functions to kill harmful bacteria and parasites that may be ingested with food and to aid digestion|
|ECL cells||Histamine||Binds to H2 receptors on parietal cells to promote HCl secretion|
|G cells||Gastrin||Promotes HCl secretion by either directly stimulating parietal cells or binding to ECL cells|
|D cells||Somatostatin||Causes inhibition of HCl secretion|
|Mucus cells||Mucus||Protects the stomach lining|
The acid pocket
Once emptied of food, some residual acid remains in the stomach. During meals, this acid is neutralised by the food ingested, causing the production of new acid. This new acid sits on top of the ingested food and neutralised acid. This is known as the postprandial acid pocket and contributes to reflux.
Food ingestion increases acid secretion by:
- Stretching the stomach walls
- Peptide-based stimulation of the G cells
- Increasing stomach pH
Pathophysiology and complications of reflux
Reflux can occur due to a number of factors. These can include:
- Hiatus hernia
- Low lower oesophageal sphincter pressure
- The acid pocket (and its proximity to the gastroesophageal junction)
Complications can arise as a result of reflux and gastro-oesophageal reflux disease, such as:
- Peptic strictures
- Barrett’s oesophagus
- Oesophageal adenocarcinoma