EsophagusThe esophagus (oesophagus) is a 25 cm long fibromuscular tube extending from the pharynx (C6 level) to the stomach (T11 level). It consists of muscles that run both longitudinally and circularly, entering into the abdominal cavity via the right crus of the diaphragm at the level of the tenth thoracic vertebrae. It actively facilitates the passage of the food bolus into the stomach under precise nervous regulation. Therefore, it is part of the digestive system.
In this page we’ll learn more about this control, as well as the anatomy, sphincters, blood supply, and innervation of the esophagus.
|Course||Oral cavity -> mediastinum -> right crus of diaphragm -> stomach|
|Innervation||Esophageal nervous plexus|
|Blood supply||Esophageal branches of the thoracic aorta, azygos, hemiazygos, accessory hemiazygos veins|
|Lymphatics||Inferior deep cervical, posterior mediastinal, intercostal, paratracheal, superior and inferior tracheobronchial lymph nodes|
Mucosa: nonkeratinized stratified squamous epithelium, lamina propria, smooth muscle layers
Submucosa: esophageal glands and papillae
Muscularis externa: striated muscle on the upper third, smooth and striated muscles in the middle third, smooth muscle in the lower third
Adventitia: fibroareolar adventitia
The esophagus is divided into three parts:
- Cervical which travels through the neck
- Thoracic which is located in the thorax, more specifically in the mediastinum
- Abdominal which travels past the diaphragm into the abdomen, reaching the stomach
As you might have guessed, the esophagus doesn’t simply float in mid-air. Throughout its course, it is closely related with many structures. The trachea and esophagus travel closely together through the neck, with the vertebral column situated posterior to the esophagus. The thoracic part passes the great vessels and nerves of the thorax, travelling very closely to the thoracic aorta and azygos vein. After piercing the diaphragm through the esophageal hiatus, the abdominal part continues close to the left lobe of the liver, finally ending in the stomach.
It can get quite confusing, right? Take note that these are merely the largest and most important related structures. Several other structures border the esophagus throughout its journey, so here’s an esophageal diagram that provides you with an overview of all of them!
Since in anatomy form follows function, it is quite easy to predict the esophagus function – it transports saliva, liquids, and solids all the way to the stomach. Through the action of both skeletal and smooth muscle fibers, the esophagus is capable of creating waves of peristalsis that actively push the contents down the digestive system.
If you want to learn more about the anatomy of the esophagus, as well as its neighboring structures, take a look at the following resources!
Since the esophagus is the third section of the gastrointestinal tract, it is connected at either end by other structures, resulting in two junctions:
- Pharyngoesophageal junction located posterior to the cricoid cartilage and formed at the union between the pharynx and the esophagus.
- Gastroesophageal junction located at the meeting point between the esophagus and the stomach.
The passage of the food bolus through these junctions is regulated by sphincters; bundles of muscle fibers under involuntary control. The pharyngoesophageal junction is surrounded by the upper esophageal sphincter, also known as the cricopharyngeus muscle. This muscle is actually a portion of the inferior pharyngeal constrictor. In turn, the gastroesophageal junction is surrounded by the lower esophageal sphincter, also known as the cardiac sphincter.
When food or liquids are transported by peristaltic waves and approach the sphincters, reflex pathways cause the muscles to temporarily relax and open, allowing the bolus to pass. At all other times, these sphincters are fully contracted and closed in order to prevent the reflux of food particles or gastric acid into previous segments of the digestive tract.
Now that we’ve seen the main parts and junctions of the esophagus, it’s time to look at its neurovasculature. We’ll firstly begin by looking at the arterial blood supply. The arteries supplying the esophagus are generally named ‘esophageal arteries’. The only difference between them is given by their origins according to the different esophagus divisions:
- Those supplying the cervical part originate from the inferior thyroid artery, a branch of the thyrocervical trunk of the subclavian artery.
- The thoracic aorta sends esophageal arteries towards the thoracic part.
- The abdominal part is supplied by arteries from the left gastric artery, a branch of the celiac trunk.
The veins follow a similar logic to the arteries. The vessels draining the esophagus of deoxygenated blood are called ‘esophageal veins’. They differ according to the vessels into which they flow:
- Veins from the cervical part drain into the inferior thyroid veins.
- The thoracic part is drained by veins that flow into the azygos and hemiazygos venous systems, as well as into the intercostal and bronchial veins.
- The vessels from the abdominal part open into the left and short gastric veins.
As you know, you cannot purposefully control your esophagus, hence it is under involuntary control by the autonomic nervous system. The parasympathetic component of the cervical part is supplied by the recurrent laryngeal nerve (a branch of the vagus nerve (CN X)) while the sympathetic fibers arise from the cervical sympathetic trunk.
The thoracic part of the esophagus is innervated by the esophageal plexus, an autonomic nervous network surrounding the esophagus. The parasympathetic component of the plexus originates from the vagus nerve, while the sympathetic fibers also stem from the sympathetic trunk running along the neck.
In contrast to the previous two, the abdominal part of the esophagus is slightly different. Its parasympathetic innervation arises from the thoracic esophageal nervous plexus, while its sympathetic component originates from the fifth to twelfth thoracic spinal nerves (T5-T12).
Via a tightly regulated interplay between the parasympathetic and sympathetic branches, the tone of the esophageal sphincters is maintained, their transitory relaxation is permitted, and peristalsis along the entire esophagus takes place.
If you want to find out more about the intricate innervation of the esophagus, simply take a sneak peek below! There you will also find a special quiz about the esophagus anatomy which covers the structure, blood supply and nerves of the esophagus!