Reflux means a backflow of liquid in the body. Most commonly it is used for the backflow of contents from the stomach into the oesophagus, usually occasioned by a weak or malfunctioning Lower Oesophageal Sphincter (LOS). This is known as Gastro-Oesophageal Reflux (GOR) and if it persists it is called Gastro-Oesophageal Reflux Disorder (or sometimes Disease) - GORD for short.
The LOS works with the muscles of the crural diaphragm (at the base of the ribcage and used in breathing) to hold the oesophagus shut most of the time. However, when our bodies are in an upright position, occasional transient relaxation of the muscles is permitted to release gas - as a burp or belch.
For many people, the Lower Oesophageal Spincter doesn't work as well as it should permitting stomach contents to flow back into the oesophagus.
One of the most common reasons for this is a hiatus hernia. The hiatus is the hole in the diaphragm the oesophagus passes through just above its junction with the stomach. In many people, the top of the stomach can push up through this hole. Known as a hiatus hernia, we don't always know why this happens. Some people may have been born with a larger hiatus enabling herniation to occur at a young age. For others, the upward pressure caused by excess body fat may be the contributing factor.
For most people a hiatus hernia will cause no problems but for others, their sphincter muscles may not be strong enough to keep the end of the oesophagus tightly closed.
Excess body weight and abdominal fat can put pressure on the stomach pushing the contents back up the oesophagus, but even fit, normal weight people can experience reflux. Amongst other causes may be tight clothing, vigorous exercise after food or simply bending over. If the LOS isn't functioning properly, stomach contents may be forced back through it.
Heartburn is the symptom most commonly associated with acid reflux but 30% of those with acid reflux report not having experienced it for some reason. The pain is from the acid attacking the top layer of the oesophagus. It may be those who don't experience the pain are less susceptible to pain, the mucous dilutes the acid sufficiently for it not to burn ar their cells may have become desensitised by transformation (e.g. from squamous to columnar as occurs with Barrett's Oesophagus). Prolonged acid attack can cause scarring and inflammation called oesophagitis.
The term, Non-Erosive Reflux Disorder (NERD) may be used when someone has GORD but without acid.
Extra-Oesophageal Reflux (also known as LaryngoPharyngeal Reflux (LPR) or Silent Reflux)
If GOR occurs, material may continue to the top of the oesophagus where it joins the trachea at the back of the throat. There is a weak flap valve here that is normally closed over the entrance of the oesophagus to allow respiration to occur. It automatically opens when swallowing to permit food to pass into the oesophagus rather than the lungs. It is controlled by the cricopharyngeal muscle. Although it may spasm, giving a “lump in the throat” feeling (called globus), it isn't very effective at stopping reflux which can aspirate throughout the respiratory system.