The oesophagus is a fibromuscular organ joining the pharynx and stomach, allowing the passage of food through peristaltic contractions. It measures around 27 cm in length and is predominantly contained within the thoracic cavity.
The oesophagus develops from embryonic gut tube from the endoderm, subsequently developing into the foregut tube. Its innervation originates from the 4th pharyngeal arch.
Begins at C6 and runs inferiorly to T11.
The oesophagus descends anterior to the vertebral bodies in the mid-line before moving anteriorly and left as it approaches the diaphragm. Its anatomical relations are as follows:
- Anterior: trachea at T4/5, recurrent laryngeal nerves, left bronchus, left atrium, diaphragm
- Posterior: Vertebrae, hemiazygos vein, descending aorta, thoracic duct
- Left: aorta, left subclavian artery and lung
- Right: Lung and azygos vein
There are three main levels at which constriction of the oesophagus can occur:
- The level of the cricoid cartilage (at its origin),15 cm from the mouth (as measured during endoscopy)
- Where it lies posterior to aortic arch and left main bronchus at 27cm from the mouth
- The diaphragmatic orifice at T10 level at 40cm from the mouth
Predominantly consists of non-keratinised stratified squamous epithelium, a smooth lamina propria and a muscularis propria containing both striated and smooth muscle. The muscularis layer is thich and contains both longitudinal and circular muscle. Adventitia line the oesophagus externally.
Columnar epithelium lines the last 0.5 cm, which produce mucus to counteract the acidic environment of stomach. Mucus-producing glands are also located in the lamina propria to aid smooth peristalsis.
The blood supply to the oesophagus is split into three regions, with communication existing between vessels of different regions:
- Upper third: inferior thyroid artery and vein
- Middle third: aortic arterial branches and azygos venous branches
- Lower third: left gastric artery and vein (branch of portal vein)
The innervation of the oesophagus is complex and come from the branches of the vagus nerve and sympathetic trunks. Sensation and motor components are generally both supplied by the left and right vagus nerves (CN X), with sympathetic fibres also contributing. The oesophageal plexus is formed from fibres from the left (mainly anterior vagal trunk) and right (mainly posterior vagal trunk) vagus nerves.
The third part of the swallow reflex involves the unconscious contraction of oesophageal muscle in a sequential fashion producing peristalsis and moving the food bolus towards the lower oesophageal sphincter. The two sphincters (upper and lower oesophageal) of the oesophagus are functional as opposed to anatomical sphincters and reduce reflux.
Gastro-oesophageal reflux: secondary to dysfunction of lower oesophageal sphincter
Barrett’s oesophagus: An example of metaplasia, where chronic gastro-oesophageal reflux causes stratified squamous epithelium to change to columnar epithelium. It is a pre-malignant condition and requires regular follow-up with endoscopy.
Oesophageal cancer: There are two main histological types of oesophageal cancer - squamous (occurring in the middle third of the oesophagus) and columnar epithelium (the lower third). Risk factors include smoking and excess alcohol intake.
Achalasia: A condition where the lower oesophageal smooth musculature fails to relax, together with the lower oesophageal sphincter. Classically a ‘swan-neck’ deformity is seen on barium swallow studies.
Developmental precursor - foregut
Arteries: Inferior thyroid (originates from the thyrocervical trunk), aortic branches and left gastric (coeliac plexus)
Veins: Inferior thyroid (drains directly into the brachiocephalic vein), azygos vein and left gastric vein (portal vein)
Vagus nerve (CN X) and cervical/thoracic sympathetic nerves
Drains into the deep cervical, posterior mediastinal and left gastric lymph nodes
The level of the oesophageal aperture in the diaphragm can be remembered by the fact the word oesophagus has ten letters – therefore its aperture is at T10.
The oesophagus is a muscular tube passing from the pharynx into the abdomen via the thoracic cavity. Particularly important are the levels at which the oesophagus can be constricted, as these are the areas that can cause difficulty when passing an endoscope.
Drake, Richard L et al. Gray's Anatomy For Students. Philadelphia: Elsevier/Churchill Livingstone, 2005, p192-5
Instant Anatomy: The oesophagus. Last accessed 11th February 2016. Available from: http://www.instantanatomy.net/thorax/areas/oesophagus.html