The oesophagus is a hollow viscous that connects the pharynx to the stomach.
The oesophagus is a muscular tube, about 25 cm in length, which is continuous with the laryngopharynx superiorly and the stomach inferiorly. It begins at the inferior border of the cricoid cartilage and C6; the gastro-oesophageal junction usually lies at T11. It is typically considered in three parts, based on the body cavities it runs through:
- The cervical oesophagus, most superior of the three, begins at the junction with the laryngopharynx and passes inferiorly to enter the thorax through the thoracic inlet
- The thoracic oesophagus, the longest part, descends from the thoracic inlet to the diaphragm, which it pierces (through the oesophageal hiatus) to enter the abdominal cavity.
- The abdominal oespohagus is a short segment (1.5 - 2 cm) that unites with the stomach at the gastro-oesophageal junction
There are several narrowings of the oesophagus which are related to sphincters or neighbouring structures
- The junction of the oesophagus and laryngopharynx (15 cm from incisor teeth)
- As the aortic arch passes anteriorly (22.5 cm from incisor teeth)
- As the left main bronchus passes anteriorly (27.5 cm from incisor teeth)
- At the gastro-oesophageal junction (40 cm from incisor teeth)
These provide important landmarks on gastroscopy.
The cervical oesophagus is related:
- Anteriorly with the trachea
- Anterolaterally with the thyroid gland and recurrent laryngeal nerves
- Laterally with the common carotid artery, with the internal jugular vein beyond this
- Posteriorly with the pre-vertebral muscles (longus colli) and the vertebral bodies of C6 and C7
The thoracic oesophagus has numerous relations:
- Above the roots of the lungs:
- Anteriorly with the trachea; the oesophagus is crossed by the left main bronchus, brachiocephalic artery and left brachiocephalic vein
- Anterior and right with the brachiocephalic artery and right common carotid.
- Anterior and left with the aortic arch and left common carotid
- Laterally with the pleura and lungs; the azygos vein passes across its right lateral surface to reach the superior vena cava
- Posteriorly with the thoracic vertebral bodies T1-T4
- Below the roots of the lungs:
- The heart lies anteriorly, separated by the pericardium
- The azygos vein lies posteriorly, often separated by a segment of pleura and lung. The vertebral bodies of T5-T10 are also posterior.
- The descending thoracic aorta is left lateral
- The vagus nerves descend laterally before becoming the oesophageal plexus; they accompany the oesophagus through the oesophageal hiatus to reach the abdomen
The abdominal oesophagus has few relations:
- The left lobe of the liver lies anteriorly and right lateral
- The left diaphragmatic crus and left inferior phrenic artery lie posteriorly; separating the oesophagus from the vertebral body of T11
- The stomach is left lateral
The oesophagus has four histologically distinct layers:
- The mucosa lines the lumen of the oesophagus.
- The epithelium is normally stratified squmaous of non-keratinising type. Metaplastic change to simple columnar epithelium can be seen in the distal oesophagus
- The lamina propria contains numerous vessels and nerves in connective tissue
- The boundary between epithelium and lamina propria is uneven, with papillae of connective tissue serving as anchors for the overlying mucosa.
- The muscularis mucosae is a narrow band of smooth muscle that forms the outer component of the mucosa. The fibres are usually arranged longitudinally, except at the gastro-oesophageal junction.
- The submucosa lies between the mucosa and muscularis externa; it is an elastic tissue and contains oesophageal glands. These glands are tubuloacinar and are found in greatest density adjacent to the gastro-oesophageal junction
- The muscularis externa consists of two thick layers (total width ≈ 300 μm); the inner layer is circular and the outer layer longitudinal
- The muscle coat is interesting as it is comprised of striated muscle for the upper third; mixed striated and smooth for the middle third, and smooth muscle only for the lower third of the oesophagus
- The adventitia is thin and formed by loose connective tissue. In the abdominal oesophagus there is an additional serosal layer of peritoneum in the adventitia.