STRUCTURE

• It is a physiological structure and cannot be demonstrated anatomically i.e. It cannot be distinguished from adjacent tissues by cellular structure or arrangement but by its function. It is present at Z-line of stomach (area where stratified squamous epithelium of esophagus changes to columnar epithelium of stomach).
• Its area overlaps between esophagus and stomach hence has both kinds of cells above mentioned.

FUNCTION

It functions as follows:

• When bolus of food is swallowed it travels down the esophagus. At it reaches the lower end, Cardiac Sphincter relaxes and allows the entry of food into the stomach.
• When stomach releases its acidic secretions for digestion of food the sphincter contracts and closes the passage between stomach and esophagus. So, no food or acid can go back upwards into the esophagus. Hence it protects esophagus from acidic contents of stomach.
• During vomit it relaxes itself allowing backwards flow of vomitus.

CLINICAL SIGNIFICANCE

People having weak Cardiac Sphincter develop Gastroesophageal Reflux Disease (GERD). In this condition there is a backflow of acidic food from stomach causing damage to esophagus and pain known as Heartburn.

Cardiac Sphincter can develop cancer due to damage by stomach acid.

Ulcers can develop at place of Cardiac Sphincter due the damage caused by Stomach acid and enzymes.

Defect in Cardiac Sphincter to relax properly results in a disorder named Achalasia.