The gastric cardia is a small but functionally significant part of the upper gastrointestinal tract. It represents the point where the esophagus connects to the stomach, acting as the entry gate for everything swallowed. The cardia is the first segment of the stomach closest to the esophagus. Its primary function is controlling the passage of food and preventing the backflow of stomach contents. Understanding this junction is important because its failure is the root cause of widespread digestive issues and long-term health risks.
Location and Normal Function
The cardia is not a separate organ but a descriptive term for the zone surrounding the opening between the esophagus and the stomach. It is located just below the diaphragm and above the dome-shaped fundus. Within this area is the lower esophageal sphincter (LES), a muscular ring that acts as a one-way valve.
The LES is made of involuntary muscle and remains closed most of the time to maintain a pressure barrier. When a person swallows, the esophagus contracts in a wave-like motion, and the LES briefly relaxes to allow food and liquids to pass into the stomach. Once the contents have moved through, the sphincter muscle quickly tightens again, sealing the gateway.
This sealing action keeps the highly acidic gastric juices contained within the stomach. The gastric cardia itself contains specialized glands that secrete a protective layer of mucus. This mucus helps shield the stomach lining from the hydrochloric acid and digestive enzymes.
Failure of the Valve and Acid Reflux
Dysfunction of the lower esophageal sphincter (LES) is the primary cause of acid reflux, which occurs when stomach contents flow back up into the esophagus. This backflow happens when the LES weakens over time or relaxes inappropriately. When the valve fails to close tightly, acidic fluid splashes back into the unprotected esophagus.
The LES can relax transiently, meaning it opens spontaneously and briefly outside of swallowing, which is a common mechanism for reflux. Chronic or frequent acid backflow is known as Gastroesophageal Reflux Disease (GERD). Common symptoms of GERD include heartburn and regurgitation, where sour or bitter fluid reaches the throat or mouth.
Several factors contribute to a weakened or poorly functioning LES. Increased pressure inside the abdomen, such as from obesity or overeating, can physically push the sphincter open. A hiatal hernia, where part of the stomach slides up into the chest cavity, can also compromise the LES’s ability to seal effectively. Additionally, substances like alcohol, nicotine from smoking, and some medications can directly cause the sphincter muscles to relax, enabling reflux.
Structural Changes and Cancer Risk
The delicate lining of the esophagus is composed of squamous cells, which are not designed to withstand the harsh acidity of stomach fluid. Chronic exposure to the refluxate causes irritation and inflammation, known as esophagitis. Over time, the esophageal lining can undergo a fundamental change in cell type to protect itself from continuous chemical injury.
This adaptive process is called metaplasia, where normal squamous cells are replaced by columnar cells resembling the intestinal lining. This change is known as Barrett’s Esophagus, the only known precursor for esophageal adenocarcinoma (EAC).
The progression from metaplasia to cancer involves distinct cellular changes, advancing first to low-grade dysplasia (LGD) and then high-grade dysplasia (HGD). Dysplasia represents abnormal cell growth and architecture, indicating a heightened risk for malignancy. The risk increases significantly for those diagnosed with LGD and HGD.
Adenocarcinoma of the gastric cardia, closely related to EAC, has seen an increasing incidence. This cancer type is associated with the damage caused by chronic reflux and the resulting metaplastic changes.