Hi there! It’s Matt from Kenhub, and in this tutorial, we will be discussing the esophagus. The esophagus – seen here highlighted in green on these images – is a long, fibromuscular tube that runs in the thoracic cavity and connects the pharynx with the stomach. It runs from below the cricoid cartilage at the level of C6 to the cardiac of the stomach. In this tutorial, we will highlight the main anatomical features of the esophagus including its constrictions and sphincters and its histological layers.
The esophagus is the third section of the alimentary canal after the oral cavity and the pharynx. The cervical part of the esophagus is situated in front of the cervical part of the vertebral column. The overall musculature of the esophagus runs both longitudinally and circularly for about twenty two centimeters utilizing both skeletal muscle on the superior third and smooth muscle on the inferior two-thirds.
The esophagus passes through the mediastinum in both the superior and the inferior-posterior sections before entering the abdominal cavity by passing through the right crus of the diaphragm at the level of the tenth thoracic vertebra. It continues below the diaphragm for approximately another two centimeters before merging with the stomach.
The esophagus is innervated by the esophageal nervous plexus that is comprised of fibers stemming from the right and left vagus nerves which contains sympathetic fibers. The arterial supply is governed by the esophageal branches of the thoracic aorta and the venous drainage occurs via the azygos, hemiazygos and accessory azygos veins. It is quite an extensive lymphatic drainage network which contains several groups of lymph nodes including the inferior deep cervical nodes, the posterior mediastinal nodes, the intercostal nodes, the paratracheal nodes and the superior and inferior tracheobronchial nodes.
The lining of the esophagus is comprised of four main layers which will be mentioned in an order going from medial to distal. The first is the mucosa which is divided further into three sublayers. The nonkeratinized stratified squamous epithelium is rapidly turned over and functions as a protective layer against food, saliva and mucus. Underneath the epithelial layer sits a sparse layer of lamina propria and, finally, a smooth muscle layer. The submucosa is next and contains mucus-secreting glands known as the esophageal glands and papillae comprising of connective tissue.
The muscularis externa or muscularis proper is made of striated muscle on the upper third, smooth and striated muscle on the middle third, and just smooth muscle on the lower third. This is due to the different functions that the upper third performs such as swallowing. The last layer is the fibroareolar adventitia.
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