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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.

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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.

Further reading:

Acid secretion

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

Further reading:

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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:

  • Oesophagitis
  • Peptic strictures
  • Barrett’s oesophagus
  • Oesophageal adenocarcinoma

Further reading:

This content hub is funded by RB. The view and opinions presented here represent those of the doctors and do not reflect those of RB.

UK/G-NHS/0818/0015b
Date of preparation: February 2019

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