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Sphincters
Sphincters
What is a sphincter?
Sphincters perform the role of valves in various systems of the human body. They are normally comprised of a smooth muscular ring that can tighten to prevent the backwards flow of matter though the conduits they protect.
There are around 60 sphincters in the human body. Six of them are part of the digestive tract.
If matter flows backwards through a sphincter, it is called reflux.
Although only the oesophageal sphincters are strictly the province of this encyclopaedia, the other sphincters of the digestive tract have been included for completeness.
1. The Upper Oesophageal Sphincter (UOS / UES).
1. The Upper Oesophageal Sphincter (UOS / UES).
The UOS exists to permit air to enter the trachea when breathing but to send food down the oesophagus when swallowing.
The main muscle controlling the UOS is the cricopharyngeus.
Reflux here, is properly termed "extra oesophageal reflux" but commonly called LPR (see this chapter). It can cause problems if refluxate aspirates into the respiratory system.
In an attempt to prevent reflux here, the cricopharyngeus muscle may spasm or tighten providing the sensation of something stuck in the throat, which is known as Globus.
The sequence of images below shows the process of swallowing.
2. The Lower Oesophageal Sphincter (LOS / LES)
2. The Lower Oesophageal Sphincter (LOS / LES)
This is the sphincter usually thought of when people speak of reflux. Reflux here will permit contents from the stomach to splash back into the oesophagus. That is frequently called Acid Reflux or Gastro-(O)Esophageal Reflux Disorder (GORD / GERD).
The sphincter comprises the diaphragm and the phrenoesophageal ligament which between them pinch the oesophagus tube tight shut when not delivering a food bolus to the stomach. (See this chapter.)
3. The Pyloric Sphincter
3. The Pyloric Sphincter
Once food has been broken down to chyme, it flows out of the stomach along the pyloric canal (on the left of this diagram) and through the pyloric sphincter into the duodenum where it will meet bile to help with digestion.
Some reflux of bile may be permitted via the pyloric sphincter to assist in breaking down fats. (See this chapter.)
4. Sphincter of Oddi
4. Sphincter of Oddi
Bile is produced in the liver and stored in the gall bladder until needed whence it is delivered via the bile duct and the sphincter of Oddi into the duodenum. (See this chapter.)
Problems with this sphincter may cause pain and be described as Sphincter of Oddi Dysfunction (SOD).
5. Ileocecal Sphincter
5. Ileocecal Sphincter
This sphincter marks the end of the small intestine (ileum),and where it joins the large intestine. Effectively absorption as part of digestion has finished and waste collection and storage has begun.
6. Anal Sphincters
6. Anal Sphincters
There are actually two sphincters together here. The inner anal sphincter, like other sphincters, has an involuntary action and the outer anal sphincter is under conscious control so we may control when we defecate.
Burps
Burps
Gas forms in the stomach for various reasons: air may be ingested along with food (aerophagia) and gasses may result from the chemical processes in breaking the food up, particularly with cruciferous vegetables like cabbage etc.
The dome shaped top of the stomach, the fundus, collects gas in the stomach until it can let it escape via a Transient Lower Oesophageal Sphincter Relaxation (TLOSR) when the LOS opens sufficiently to let it escape as a burp. Most TLOSRs are minor and gentle and we may even be unaware of them. However, if pressure builds up, a more explosive TLOSR may occur.
For those of us with reflux, the LOS may try to remain tight shut a little longer resulting in a more likely build up of gas pressure and a more obvious burp.
A tip for refluxers to control the burp and release bloat pressure, is to sip sparkling water or soda whilst keeping upright and possibly following with gentle pressing on the stomach to produce a controlled burp, while the body is in an upright position.
Supragastric Belch
Supragastric Belch
This describes a violent belch after involuntarily gasping in air, rather than producing and expelling it as a acid reflux burp without the typical stomach distension associated with traditional gastric belching. This type of belch originates from above the stomach, typically in the throat or upper esophagus.
Hiccups
Hiccups
When the stomach touches the diaphragm, a shock wave is created. That's a hiccup.
That is more likely to ocur when the fundus of the stomach is inflated by retention of the gas to permit a better burp.
Page updated 10 January 2024
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