Esophagus

The esophagus is an organ in vertebrates which consists of a fibromuscular tube through which food passes, aided by peristaltic contractions, from the pharynx to the stomach. The esophagus travels behind the trachea and heart, passes through the diaphragm and empties into the cardia of the stomach.

The wall of the esophagus from the lumen outwards consists of mucosa, sub-mucosa (connective tissue), layers of muscle fibers between layers of fibrous tissue, and an outer layer of connective tissue. Most of the muscle is smooth muscle although striated muscle predominates in its upper third. It has two muscular rings or sphincters in its wall, one at the top and one at the bottom. The lower sphincter helps to prevent reflux of acidic stomach content. The esophagus has a rich blood supply and vascular drainage. Its smooth muscle is innervated by involuntary nerves (sympathetic nerves via the sympathetic trunk and parasympathetic nerves via the vagus nerve) and in addition voluntary nerves (lower motor neurons) are carried in the vagus nerve to innervate its striated muscle.