The Anatomy of the Esophagus

The esophagus is the muscular tube that connects the back of the throat (or pharynx) with the stomach. Its main job is to deliver food, liquids, and saliva to the rest of the digestive system. Along its course, it runs down the neck, through the thorax (chest cavity), before entering the abdominal cavity, which contains the stomach.

This essential organ can be impacted by a number of health conditions—most commonly gastroesophageal reflux disease (GERD), but also esophageal cancer, heartburn, and eosinophilic esophagitis, among others. Since it’s such a crucial part of the body, it’s important to get a sense of what the esophagus is, what it does, as well as what conditions can impact it.      

Anatomy

Every feature of esophageal anatomy reflects its purpose as part of the system that delivers nutrition and liquid through the body.

Structure

In fully-grown adults, the esophagus is a cylinder of approximately 9 to 10 inches or 23 to 25 centimeters (cm) in length and is generally a little over 1 inch (3 cm) in diameter. It’s composed of four layers of tissues and muscles:

• Mucosa: The inner lining of the esophagus is a layer of soft tissue, called the mucosa (or innermost mucosa), is itself composed of three layers. Its exterior, the epithelium, is composed of protective cells, with layers of connective tissue (lamina propria) and thin bands of smooth muscle (muscularis mucosa). This layer is also lined with glands, which aid in digestion.       
• Submucosa: This inner layer is thick and fibrous, serving to connect the mucosa to the muscularis externa. Along with the mucosa, this layer causes folds running down the esophagus. As such, viewed from above, this organ forms a star shape.
• Muscularis: This muscular layer is sub-divided into an inner portion composed of circular muscle fibers, and an outer portion of descending fibers.
• Tunica adventitia: This outer layer of fibrous tissue serves as a kind of scaffolding for the esophagus, affixing it to surrounding structures to hold it in place.

Importantly, the musculature of the esophagus varies as it travels downward. The upper third of this organ is primarily voluntary (striated) muscle; the middle third is a mixture of voluntary and involuntary (smooth) muscle, and the lower third is composed of only involuntary muscle.

Location

Connecting the rear portion of the pharynx (hypopharynx) to the stomach, the esophagus runs downward, crossing into the chest and abdominal cavities. The anatomy of the esophagus is divided into three sections based on this course:

• Cervical: The upper portion of the esophagus travels through the neck, sitting just in front of the spinal column, and just behind the trachea, or windpipe. Where it emerges from the pharynx, at the pharyngoesophageal junction, is a bundle of involuntary muscle called the upper esophageal sphincter (UES), a kind of door to the organ.
• Thoracic: As the esophagus travels downward, it accesses a portion of the thorax called the mediastinum, traveling near some of the most important arteries and veins in the body. Here, it runs parallel to the thoracic portion of the aorta (the major artery of the heart), and the azygos vein (which carries blood from the thorax back to the heart), while crossing other important vessels.
• Abdominal: At the level of the lowest rib, the esophagus passes into the abdominal cavity through the diaphragm—the major muscles of breathing—by way of an opening called the esophageal hiatus. Once in this cavity, it travels downward next to the left lobe of the liver, before terminating at the stomach. This meeting point, the gastroesophageal junction, is surrounded by another bundle of involuntary muscle, the lower esophageal sphincter.

Anatomical Variations

Generally speaking, variations to the esophagus’s anatomy are extremely rare. Most that do occur have to do with small variations in the length of this organ. However, significant and impactful congenital abnormalities do arise. These include:

• Tracheoesophageal (TE) fistula and atresia: In the former case, the esophagus, which should be separate from the trachea, is connected to it. When those with TE fistula swallow, liquid can cross into the lungs. This condition is often accompanied by atresia, in which the esophagus forms into two parts, rather than one.
• Esophageal stenosis: Under-development of the esophagus at birth can also lead to stricture, a narrowing of the canal. This is a very rare disorder, occurring in one in every 25 to 50,000 live births.
• Esophageal duplication and duplication cyst: Duplication of the entire esophagus occurs very rarely; however, partial duplication, leading to the growth of noncancerous cysts is more common. These tend to occur in the lower portions of the esophagus.
• Esophageal rings and webs: Rings and webs are folds of esophageal tissue that partially or completely obstruct the esophagus. The former of these refers to when these obstructions occur in the lower esophagus; whereas the latter is when there’s a thin layer of cells blocking off some or all of the upper esophagus.

Function

As the upper portion of the digestive system, the esophagus’s primary role is to carry food and liquid down to the stomach. When you swallow, your brain activates the muscles of the upper esophageal sphincter (UES), opening it up, while also stimulating others to block off the trachea.

Once material enters the esophagus, the stress placed on the walls stimulates nerve cells in them, initiating what’s called “peristalsis.” The esophageal muscles first relax, and then squeeze from top to bottom, pushing food down to the stomach.

The lower esophageal sphincter, at the base of the esophagus, then acts as a valve, opening to let food pass through to the stomach, but closing to prevent stomach acids from flowing upward.

A secondary role of the esophagus is during vomiting, when you expel food or drink from the stomach. In response to nausea, certain centers in the brain are activated, leading to retching, or dry heaving. As you do so, muscles surrounding the stomach start to contract and relax, and the lower esophageal sphincter opens up.

During the final stage of vomiting, abdominal muscles tighten to pressure the stomach, while the diaphragm contracts and opens up the esophagus. This then forces food and liquids out of the body.   

Associated Conditions

A number of conditions can impact the esophagus, ranging from the relatively mild to the much more serious. Disorders and diseases here can arise independently or be part of an underlying condition.

Here’s a quick breakdown of the most common esophageal conditions:

• Achalasia (dysphagia): Difficulty swallowing can arise for many reasons and represent a disorder of the esophagus. Heartburn and chest pains frequently accompany achalasia.
• Gastroesophageal reflux disease (GERD): Heartburn occurs when stomach acids flush back upwards because the lower esophageal sphincter doesn’t close properly, causing chest pains. GERD is a form of chronic and severe heartburn that also leads to coughing, wheezing, nausea, painful swallowing, and vomiting.
• Eosinophilic esophagitis (EoE): This is a chronic immune or allergic reaction of the esophagus, in which white blood cells accumulate in the inner lining. This leads to inflammation, causing difficulties swallowing, decreased appetite, abdominal pain, and vomiting.
• Esophageal cancer: Cancer cells can develop in the inside lining of the esophagus, eventually spreading through the other layers. This organ is affected by two types of cancer, defined by the type of cells that they originated in—squamous cell carcinoma and adenocarcinoma.
• Barrett’s esophagus: Often associated with GERD, in this condition, damage to esophageal tissues may or may not cause heartburn symptoms, but always increases the risk of developing adenocarcinoma.   
• Esophageal stricture: The abnormal tightening of the esophagus can arise at birth (as discussed above), be the result of cancer or GERD, or arise as a result of radiation therapy, previous surgery, medications, or stomach ulcers.

Treatment

Treating conditions of the esophagus mean either taking on heartburn and other symptoms or going after any underlying condition that’s causing problems. Everything from lifestyle changes to surgery can be used to take on these diseases and disorder. Common treatment approaches include:

• Lifestyle management: Heartburn resulting from GERD or other conditions can be taken on with changes to diet and lifestyle. While avoiding foods that trigger acid reflux, eating slowly, losing weight, quitting smoking, and other changes may not always eradicate the issue, they can certainly help.
• Medications: Several kinds of medications are prescribed to take on chronic heartburn, including histamine blockers such as Tagamet (cimetidine) and Pepcid (famotidine), proton pump inhibitors (PPIs) such as Nexium (esomeprazole) and Prilosec (omeprazole), and others.  
• Esophageal cancer therapy: Treatment approaches to cancer vary a great deal based on the specific case; however, these may include radiation therapy, chemotherapy, immunotherapy, or surgery. Doctors may target and remove tumors locally, or work to kill cancer throughout the body using radiation or drugs.
• Surgery: Nissen fundoplication is a common surgical treatment for GERD in which the upper part of the stomach is wrapped around the lower esophageal sphincter (LES). This surgery strengthens the sphincter to prevent acid reflux.
• Esophageal dilation: In cases of stricture, doctors may attempt this procedure, which involves using a special tube or surgical balloon to physically open up the esophagus. This is typically an outpatient procedure, performed while you’re on local anesthetic.