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Glossary


Anatomy and physiology of the esophagus

The esophagus is an organ in the digestive system. It is part of the gastrointestinal (GI) tract, which is the tube that goes from the mouth to the anus. The GI tract includes the esophagus, stomach, small intestine and large intestine. Other organs of the digestive system include the liver, gallbladder and pancreas.

 

The esophagus is a hollow, muscular tube that allows food to pass from the mouth to the stomach. The esophagus is 25–33 cm (10–13 inches) long. It begins in the throat (pharynx) and connects to the stomach. It is less than 2.5 cm (1 inch) in diameter at its narrowest part. It lies behind the windpipe (trachea) and in front of the backbone (spine) inside the chest cavity.

 

A ring of muscle fibres form the upper esophageal sphincter, which detects food and liquids in the back of the throat and controls the passage of food into the esophagus when a person swallows. The wall of the esophagus includes 2 strong muscle layers that contract to help push food along (peristalsis) until it reaches the stomach. At the bottom of the esophagus there is another ring of muscle fibres that form the lower esophageal sphincter (also known as the cardiac sphincter).The area where the esophagus joins the stomach is called the gastroesophageal (GE) junction.

 

There are a number of lymph nodes in and around the esophagus. Lymph nodes are small bean-shaped glands that fight infection. They are connected by a network of lymph vessels.

 

Structure

Regions of the esophagus

The esophagus is divided into 3 regions:

  • cervical esophagus – begins at the back of the throat and ends at the level of the first rib and first thoracic vertebra
    • This is one of the regions where squamous cell carcinoma of the esophagus (SCCE) occurs.
  • thoracic esophagus – begins at the level of the first rib and first thoracic vertebra and ends at the level of the diaphragm
    • The thoracic esophagus is further divided into upper, middle and lower regions.
    • SCCE is more common in the upper and middle thoracic esophagus. Adenocarcinoma of the esophagus (ACE) is more common in the lower thoracic esophagus.
  • abdominal esophagus – shortest region of the esophagus that begins at the level of the diaphragm and ends where the esophagus enters the stomach
    • ACE occurs in this region.

 

Tissue layers of the esophagus

There are 3 tissue layers in the esophagus:

  • mucosa – inner lining made up of squamous cells (epithelium), lamina propria (connective tissue) and a thin layer of muscle (muscularis mucosa)
  • submucosa – layer of connective tissue that surrounds the mucosa layer and contains mucous glands, blood vessels, nerves and lymphatic tissue
  • muscularis propria (muscle) – lies outside of the submucosa layer and has an inner ring of circular muscle fibres and an outer ring of long muscle fibres that surround the wall of the esophagus

 

Unlike most of the gastrointestinal tract, the esophagus is not covered by serosa. A different outer layer of connective tissue, called the adventitia, loosely supports and covers the esophagus instead. Only the abdominal portion of the esophagus is covered by peritoneum.

 

Function

Although the esophagus is part of the digestive system, it actually does not play a role in digestion. However, it is an important organ within the GI tract. When a person swallows, the muscular walls of the esophagus contract (tighten) and push food and fluids from the mouth into the stomach for digestion. Glands in the submucosa layer produce mucus, which helps keep the inside of the esophagus moist and provides lubrication for swallowing.

 

At the GE junction, where the esophagus and stomach join, the lower esophageal sphincter acts like a valve to control the passage of food into the stomach. When it opens, the valve lets food into the stomach. When closed, it prevents the stomach contents from going back into the esophagus.

References

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