The esophagus (oesophagus) is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach. The word esophagus is derived from the Latin œsophagus, which derives from the Greek word oisophagos, lit. "entrance for eating." In humans the esophagus is continuous with the laryngeal part of the pharynx at the level of the C6 vertebra. The esophagus passes through posterior mediastinum in thorax and enters abdomen through a hole in the diaphragm at the level of the tenth thoracic vertebrae (T10). It is usually about 10–50 cm long depending on individual height. It is divided into cervical, thoracic, and abdominal parts. Due to the inferior pharyngeal constrictor muscle, the entry to the esophagus opens only when swallowing or vomiting.
The layers of the oesophagus are as follows: mucosa; nonkeratinized stratified squamous epithelium (serves a protective effect due to the high volume transit of food, saliva, and mucus); lamina propria, muscularis mucosae: smooth muscle; submucosa (contains the mucous secreting glands esophageal glands, and connective structures termed papillae); and muscularis externa (or "muscularis propria").
Normally, the esophagus has three anatomic constrictions at the following levels: at the esophageal inlet, where the pharynx joins the esophagus, behind the cricoid cartilage (14–16 cm from the incisor teeth); where its anterior surface is crossed by the aortic arch and the left bronchus (25–27 cm from the incisor teeth); and where it pierces the diaphragm (36–38 cm from the incisor teeth). The distances from the incisor teeth are important as is useful for diagnostic endoscopic procedures.
The junction between the esophagus and the stomach (the gastroesophageal junction or GE junction) is not actually considered a valve, although it is sometimes called the cardiac sphincter, cardia or cardias, it actually better resembles a structure. In much of the gastrointestinal tract, smooth muscles contract in sequence to produce a peristaltic wave which forces a ball of food (called a bolus) while in the esophagus. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract.