Upper esophageal sphincter

Esophagus
The digestive tract, with the esophagus marked.
Details
Precursor	Foregut
System	Part of the digestive system
Artery	Esophageal arteries
Vein	Esophageal veins
Nerve	Sympathetic trunk, vagus
Identifiers
Latin	Oesophagus
MeSH	A03.556.875.500
Dorlands /Elsevier	Esophagus
TA	A05.4.01.001
FMA	7131
Anatomical terminology []

The esophagus (American English) or oesophagus (British English) (/ᵻˈsɒfəɡəs/), commonly known as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the stomach. The esophagus is a tube, about 25 centimetres long in adults, which travels behind the trachea and heart, passes through the diaphragm and empties into the uppermost region of the stomach. During swallowing, the epiglottis tilts backwards to prevent food from going down the larynx and lungs. The word esophagus is the Greek word οἰσοφάγος oisophagos, meaning "gullet".

The wall of the esophagus from the lumen outwards consists of mucosa, submucosa (connective tissue), layers of muscle fibers between layers of fibrous tissue, and an outer layer of connective tissue. The mucosa is a stratified squamous epithelium of around three layers of squamous cells, which contrasts to the single layer of columnar cells of the stomach. The transition between these two types 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. The lower sphincter helps to prevent reflux of acidic stomach content. The esophagus has a rich blood supply and venous 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) which are carried in the vagus nerve to innervate its striated muscle.