Reflux esophagitis is prevented by -a) Long intraabdominal esophagusb) Increased intraabdominal pressurec) Right crus of diaphragmd) Increased intrathoracic pressure
The principle barrier to reflux is the Lower esophageal sphincter. LES comprises the lower 4 cm of esophagus, where resting pressure within the lumen normally exceeds the intragastric pressure. This high intraluminal pressure at LES prevents the GE reflux. The LES is a physiological entity rather than any anatomical structure
Several factors contribute to the high intraluminal pressure of LES 
a) Intrinsic musculature of distal esophagus

these muscle fibres differ from those in other areas of the esophagus in that they are in a state of tonic contraction. They normally relax with initiation of a swallow and then return to a state of tonic contraction.


Sling fibres of the cardia
Crura of the diaphragm
Intraabdominal pressure

- the intraabdominal pressure compresses the intraabdominal segment of esophagus (ie LES) and is probably the most important factor in preventing the reflux.
- CSDT writes - "Sphincter competance is a function of sphincter pressure, sphincter length and the length exposed to intraabdominal pressure".
- In cases of sliding hernia the gastroesophageal junction shifts to posterior mediastinum. The LES is then exposed to the low intrathoracic pressure instead of the high intraabdominal pressure. The low intrathoracic pressure is unable to prevent the reflux in sliding hernia.

Other factors apart from LES which prevent the reflux 


The gastroesophageal angle - the oblique entry of esophagus has a valvular effect, in that it closes the esophagus when the gastric fundus distends
The folds of mucosa at the cardia helps in closing the LES when intragastric pressure rises.


The intrathoracic pressure has no role in preventing reflux. It's too low (ranging from -5 to +5 mm of Hg).
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