The esophagus is a hollow, muscular tube that connects the throat to the stomach. Food and liquids that are swallowed travel through the inside of this tube (called the lumen) to reach the stomach. The esophagus is usually between 10 and 13 inches long. The normal adult esophagus is roughly ¾ of an inch across at its smallest point.
The wall of the esophagus has several layers. The layer that lines the inside of the esophagus is called the mucosa. The mucosa has 2 parts: the epithelium and the lamina propria. The epithelium forms the lining of the esophagus and is made up of flat, thin cells called squamous cells. The lamina propria is a thin layer of connective tissue right under the epithelium.
The next layer is the submucosa. In some parts of the esophagus, this layer contains glands that secrete mucus. The layer under the submucosa is a thick band of muscle called the muscularis propria. This layer of muscle contracts in a coordinated, rhythmic way to push food along the esophagus from the throat to the stomach. The outermost layer of the esophagus is formed by connective tissue. It is called the adventitia.
The upper part of the esophagus has a special area of muscle at its beginning that relaxes to open the esophagus when it senses food or liquid coming toward it. This muscle is called the upper esophageal sphincter. The lower part of the esophagus that connects to the stomach is called the gastroesophageal junction, or GE junction. There is a special area of muscle near the GE junction called the lower esophageal sphincter. The lower esophageal sphincter controls the movement of food from the esophagus into the stomach and it keeps the stomach’s acid and digestive enzymes out of the esophagus.
The stomach has strong acid and enzymes that digest food. The epithelium or lining of the stomach is made of glandular cells that release acid, enzymes, and mucus. These cells have special features that protect them from the stomach’s acid and digestive enzymes.
In some people, acid escapes from the stomach back into the esophagus. The medical term for this is reflux or gastroesophageal reflux disease (GERD). In many cases, reflux can cause symptoms such as heartburn or a burning feeling spreading out from the middle of the chest. But sometimes, reflux can occur without any symptoms at all. If reflux of stomach acid into the lower esophagus continues for a long time, it can damage the lining of the esophagus. This causes the squamous cells that usually line the esophagus to be replaced with glandular cells. These glandular cells usually look like the cells that line the stomach and the small intestine and are more resistant to stomach acid. The presence of glandular cells in the esophagus is known as Barrett’s (or Barrett) esophagus. People with Barrett’s esophagus are much more likely to develop cancer of the esophagus (about 30 to100 times normal). These people require close medical follow-up in order to find cancer early. Still, although they have a higher risk, most people with Barrett’s esophagus do not go on to develop cancer of the esophagus.
Cancer of the esophagus (also referred to as esophageal cancer ) starts in the inner layer (the mucosa) and grows outward (through the submucosa and the muscle layer). Since 2 types of cells line the esophagus, there are 2 main types of esophageal cancer: squamous cell carcinoma and adenocarcinoma.
The esophagus is normally lined with squamous cells. The cancer starting in these cells is called squamous cell carcinoma. This type of cancer can occur anywhere along the length of the esophagus. At one time, squamous cell carcinoma was by far the more common type of esophageal cancer in the United States, making up to 90% of all esophageal cancers. This has changed over time, and now it makes up less than 50% of esophageal cancers in this country.
Cancers that start in gland cells are called adenocarcinomas. This type of cell is not normally part of the inner lining of the esophagus. Before an adenocarcinoma can develop, glandular cells must replace an area of squamous cells, which is what happens in Barrett’s esophagus. This occurs mainly in the lower esophagus, which is the site of most adenocarcinomas.
Cancers that start at the area where the esophagus joins the stomach (the GE junction) or the first part of the stomach (called the cardia) used to be staged as stomach cancers. But because these cancers behave like esophagus cancers (and are treated like them, as well), they are now grouped with esophageal cancers.