The esophagus is a long fibromuscular tube that runs in the thoracic cavity and connects the pharynx with the stomach. This article will highlight the main anatomical features of the esophagus, including its constrictions and sphincters, its histological layers and the main pathological changes that may ail this particular organ.
It is the third section of the alimentary canal after the oral cavity and the pharynx and its musculature 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. It 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 vertebrae. It continues below the diaphragm for approximately another two centimeters before merging with the stomach. It is innervated by the esophageal nervous plexus that is comprised of fibers stemming from the right and left vagal nerves which contain 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 hemiazygos veins. It has quite anextensive 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.
Esophageal Constrictions and Sphincters
The esophagus has three main anatomical constrictions. The first occurs at the esophageal inlet where the pharynx ends and the esophagus begins, behind the cricoid cartilage. The second occurs at the point where the anterior surface of the esophagus is crossed by the aortic arch and the left bronchus in the mediastinum. The last constriction happens where the esophagus enters the crus of the diaphragm.
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 comprised 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.
Several common pathological complains that may include the esophagus are esophagitis, heartburn, achalasia and an esophageal ulcer. Esophagitis is the inflammation of the esophagus and can be due to the reflux of stomach acid or infections that have spread from the pharynx. Heartburn is a result of an incompletely closed lower esophageal sphincter which allows the stomach acid to regurgitate back into the esophagus. It can cause heartburn, coughing, hoarseness or no symptoms at all. Achalasia is the opposite of heartburn and occurs when the lower esophageal sphincter won’t relax resulting in difficulty swallowing due to regurgitation. Lastly, an esophageal ulcer is an erosion in an area of the esophageal lining and is often caused by the chronic reflux of stomach acid.