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. In humans, the esophagus is usually 18–25 centimeters long. During swallowing the epiglottis tilts backwards to prevent food from going down the larynx. The esophagus travels behind the trachea and heart, passes through the diaphragm and empties into the cardia of the stomach. The word
esophagus is derived from the Latin
oesophagus, which derives from the Greek word
oisophagos, lit. "entrance for eating." The wall of the esophagus from the lumen outwards consists of mucosa, sub-mucosa, layers of muscle fibers between layers of fibrous tissue, and an outer layer of connective tissue. The mucosa is a stratified squamous epithelium which contrasts to the single layer of columnar cells of the stomach. The transition between these two type of epithelium is visible as a zig-zag line. 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.