Understanding the digestive system.

The first stage of digestion is chewing involving teeth and saliva to make small enough pieces to swallow.

At the back of the throat, the epiglottis closes over the trachea (widpipe) so the food bolus enters the oesophagus, the food tube that passes through the chest to the stomach, instead of the lungs.

Along the length of the oesophagus, muscles squeeze the tube above the bolus to push it towards the stomach. This is called peristalsis.

In the stomach, the bolus is churned in concentrated acid to liquidise it into chyme which can pass out of the stomach into the duodenum where it meets bile and digestive enzymes to enable absorption to continue along the length of intestines.

There are various rings of muscles along the way to act as valves so the whole tract is intended to be a one way street. These are called sphincters.

At the top of the oesophagus, the upper oesophageal sphincter is composed mainly of the cricopharyngeus to permit food to remain in the oesophagus rather than the airways.

At the base of the oesophagus, the lower esophageal sphincter is joined with muscles of the diaphragm to permit matter to enter the stomach and keep it there.

If any matter flows the wrong way through any of these sphincters, it's called reflux.

Indigestion may refer to any abnormality within the digestive process.

One of the most commonly reported is heartburn which has nothing to do with the heart but is actually acid attacking the oesophagus when stomach acid refluxes via the lower oesophageal sphincter.

Gastro-Oesophageal Reflux Disorder (or Disease) "GORD" describes the condition where acid reflux occurs frequently. Not everyone who has GORD experiences the pain of heartburn.

The Oesophagus

This is a tube about 25 cm long and 2 cm wide when inactive. I liken it to a bicycle tyre inner tube.

The walls of the oesophagus comprise, from inside outwards, the mucosa, the submucosa, the muscularis propria (musculature for peristalsis) and the adventia (the outer wall).The mucosa produces mucous to lubricate and protect the oesopagus.

The stomach

In its mucosa, triggered by the ingestion of food, the stomach produces proton pumps, special cells that, by releasing protons into the gastric juices, render it highly acidic making concentrated hydrochloric acid with a pH typically of 1.