The oesophagus is a fibromuscular tube, approximately 25cm in length, that transports food from the pharynx to the stomach. It originates at the inferior border of the cricoid cartilage (C6) and extends to the cardiac orifice of the stomach (T11). In this article, we shall take a closer look at the anatomy of the oesophagus – its structure, vascular supply and clinical correlations.
The oesophagus begins in the neck, at the level of C6. Here, it is continuous superiorly with the laryngeal part of the pharynx (the laryngopharynx). It then descends downward into the superior mediastinum of the thorax, positioned between the trachea and the vertebral bodies of T1 to T4. This thoracic portion of the oesophagus is approximately 23.5cm in length. It then enters the abdomen via the oesophageal hiatus (an opening in the right crus of the diaphragm) at T10. The abdominal portion of the oesophagus is relatively short – it terminates by joining the cardiac orifice of the stomach at level of T11.
The oesophagus shares a similar structure with many of the organs in the alimentary tract – consisting of four main layers.
There are two sphincters present in the oesophagus, known as the upper and lower oesophageal sphincters. They act to prevent the entry of air and the reflux of gastric contents respectively.
The upper sphincter is an anatomical, striated muscle sphincter at the junction between the pharynx and oesophagus. It is produced by the cricopharyngeus muscle. Normally, it is constricted to prevent the entrance of air into the oesophagus.
The lower oesophageal sphincter is located at the gastro-oesophageal junction (between the stomach and oesophagus). The gastro-oesophageal junction is situated to the left of the T11 vertebra, and is marked by the change from oesophageal to gastric mucosa. The sphincter is classified as a physiological (or functional) sphincter, as it does not have any specific sphincteric muscle. Instead, the sphincter is maintained by four factors:
During oesophageal peristalsis, the sphincter is relaxed to allow food to enter the stomach. Otherwise at rest, the function of this sphincter is to prevent the reflux of acidic gastric contents into the oesophagus.
The anatomical relations of the oesophagus give rise to four physiological constrictions in its lumen – it is these areas where food/foreign objects are most likely to become impacted. The oesophagus can be remembered using the acronym 'ABCD' - Arch of aorta, Bronchus (left main stem), Cricoid cartilage, Diaphragmatic hiatus.
In respect to its arterial and venous supply, the oesophagus can be divided into its thoracic and abdominal components. The thoracic part of the oesophagus receives its arterial supply from the branches of the thoracic aorta and the inferior thyroid artery (a branch of the thyrocervical trunk). Venous drainage into the systemic circulation occurs via branches of the azygous veins and the inferior thyroid vein. The abdominal oesophagus is supplied by the left gastric artery (a branch of the coeliac trunk) and left inferior phrenic artery. This part of the oesophagus has a mixed venous drainage via two routes - To the portal circulation via left gastric vein and to the systemic circulation via the azygous vein.
The anatomy of the oesophagus is a complex but integral part of the human body. From its origin in the neck to its termination in the abdomen, the oesophagus is an essential organ used in the transport of food and fluids from the mouth to the stomach. The four layers of its structure, its anatomical relations, sphincters, course and vascular supply all play a role in ensuring its successful function.
The oesophagus, also known as the gullet or food pipe, is a fibromuscular tube, approximately 25cm in length, that transports food from the pharynx to the stomach. It originates at the inferior border of the cricoid cartilage (C6) and extends to the cardiac orifice of the stomach (T11), passing through the neck, the superior mediastinum of the thorax, and the oesophageal hiatus of the diaphragm. In this article we shall examine the anatomy of the oesophagus - its structure, vascular supply, innervation, lymphatic drainage and clinical correlations.
The oesophagus begins in the neck, at the level of C6. Here, it is continuous superiorly with the laryngeal part of the pharynx (the laryngopharynx). It descends downward into the superior mediastinum of the thorax, positioned between the trachea and the vertebral bodies of T1 to T4. It then enters the abdomen via the oesophageal hiatus (an opening in the right crus of the diaphragm) at T10. The abdominal portion of the oesophagus is approximately 1.25cm long, and terminates in the cardiac orifice of the stomach at level of T11.
The oesophagus shares a similar structure with many of the organs in the alimentary tract. It has an outer layer of connective tissue called the adventitia, which except for the very distal and intraperitoneal portion of the oesophagus, is replaced by a serosa. An external layer of longitudinal muscle and an inner layer of circular muscle make up the muscular layer, with the muscle type differing in each third. The superior third is composed entirely of voluntary striated muscle, the middle third is a combination of voluntary striated and smooth muscle, and the inferior third is composed entirely of smooth muscle. Beneath the muscular layer lies the submucosa, which is followed by non-keratinised stratified squamous epithelium, contiguous with the columnar epithelium of the stomach.
Food is transported through the oesophagus by peristalsis – rhythmic contractions of the muscular layers which propagate down the oesophagus. Hardening of these muscular layers can interfere with peristalsis and cause difficulty in swallowing (dysphagia).
Two sphincters are present in the oesophagus – the upper and lower oesophageal sphincters. The upper oesophageal sphincter prevents the entry of air, while the lower oesophageal sphincter prevents the reflux of gastric contents.
The oesophagus has a dual vascular supply. The first source is the portal venous system, which is responsible for delivering blood from the intestine to the liver directly. The second source is the systemic venous system, which is responsible for delivering oxygenated blood back to the heart via the subclavian veins. These two independent sources are connected by the porto-systemic anastomosis, a connection between the portal and systemic venous systems. Oesophageal varices form when the pressure in the portal system increases beyond normal, a state known as portal hypertension. It is usually caused by chronic liver disease, such as cirrhosis or an obstruction in the portal vein, and predisposed to bleeding, with most patients presenting with haematemesis (vomiting of blood). Alcoholics are at a high risk of developing oesophageal varices.
The oesophagus is innervated by the oesophageal plexus, which is formed by a combination of the parasympathetic vagal trunks and sympathetic fibres from the cervical and thoracic sympathetic trunks. Two different types of nerve fibre run in the vagal trunks; fibres supplying the upper oesophageal sphincter and upper striated muscle originate from the nucleus ambiguus, while those supplying the lower oesophageal sphincter and smooth muscle of the lower oesophagus arise from the dorsal motor nucleus.
The lymphatic drainage of the oesophagus is divided into thirds; the superior third drains into the deep cervical lymph nodes, the middle third to the superior and posterior mediastinal nodes, and the lower third to the left gastric and celiac nodes.
Barrett's oesophagus is a metaplastic change (reversible change from one differentiated cell type to another) of lower oesophageal squamous epithelium to gastric columnar epithelium. It is usually caused by chronic acid exposure as a result of a malfunctioning lower oesophageal sphincter, and the most common symptom is a long-term burning sensation of indigestion. Around 2% of malignancies in the UK are oesophageal carcinomas and it is characterised by dysphagia (difficulty swallowing) and weight loss. There are two major types of oesophageal carcinomas - squamous cell carcinoma and adenocarcinoma. Squamous cell carcinoma is the most common subtype of oesophagus cancer and can occur at any level of the oesophagus. Adenocarcinoma, on the other hand, only occurs in the inferior third and is associated with Barrett's oesophagus.
The upper oesophageal sphincter is an anatomical structure located at the junction between the pharynx and oesophagus. It is made up of the cricopharyngeus muscle, and acts as a striated muscle sphincter. It is responsible for maintaining closure of the oesophagus to prevent the entrance of air into it, while also serving to keep the oesophagus contents from re-entering the pharynx.
The lower oesophageal sphincter is located at the gastro-oesophageal junction between the stomach and oesophagus. This junction is situated to the left of the T11 vertebra and is marked by a change from the oesophageal to gastric mucosa. As opposed to the upper oesophageal sphincter, the lower sphincter is classified as a physiological or functional sphincter, as it does not have any specific sphincteric muscle. Rather, its action is maintained by four factors:
At rest, the sphincter's primary responsibility is to prevent the reflux of acidic gastric contents into the oesophagus. During oesophageal peristalsis however, the sphincter relaxes to allow food to enter the stomach.
The anatomical relations of the oesophagus, which include the trachea, left recurrent laryngeal nerve, pericardium, thoracic vertebral bodies, thoracic duct, azygous veins, left vagus nerve, right vagus nerve, left crus of the diaphragm, subclavian artery, and the aortic arch, give rise to four physiological constrictions in its lumen - it is these areas where food and foreign objects are most likely to become impacted. The oesophagus is most easily remembered using the acronym, ABCD (Arch of aorta, Bronchus (left main stem), Cricoid cartilage, Diaphragmatic hiatus).
In respect to its arterial and venous supply, the oesophagus can be divided into its thoracic and abdominal components. The thoracic part of the oesophagus receives its arterial supply from the branches of the thoracic aorta and the inferior thyroid artery (a branch of the thyrocervical trunk). Venous drainage into the systemic circulation occurs via branches of the azygous veins and the inferior thyroid vein. The abdominal oesophagus is supplied by the left gastric artery (a branch of the coeliac trunk) and left inferior phrenic artery. This part of the oesophagus has a mixed venous drainage via two routes- To the portal circulation via left gastric vein and to the systemic circulation via the azygous vein. In respect to its innervation, the oesophagus is innervated by the oesophageal plexus, which is formed by a combination of the parasympathetic and sympathetic fibres derived from the vagal and cervical thoracic trunks.
The oesophagus is a hollow muscular tube. Its walls are made up of four concentric layers, which are; the mucosa, submucosa, muscularis, and adventitia. These layers are responsible for regulating the movement of food along the oesophagus. Between the innermost and middle layer, two oesophageal sphincters are present, which contract to prevent backflow of gastric contents.
The lymphatic drainage of the oesophagus is divided into three sections; the superior third, which drains into the deep cervical lymph nodes, the middle third, which drains into the superior and posterior mediastinal nodes, and the lower third, which drains into the left gastric and celiac nodes.
Disorders of the oesophagus, such as Barrett's oesophagus and oesophageal carcinoma, can develop due to impaired lymphatic drainage. Oesophageal varices is a common complication in patients with cirrhosis, and is characterised by an abnormal dilation of the oesophageal veins.
