Oesophagus lining. Coloured scanning electron micrograph (SEM) of a section through the lining of the human oesophagus (gullet). The interior surface of the oesophagus is at top. The first, thick layer is the epithelium. Below this are the mucosa and submucosa layers. The epithelium has a specialised surface to cope with the passage of rough food, and the mucosal layer secretes mucus to help with this protection. There are also some thin layers of smooth muscle (not clearly seen). The oesophagus is a muscular tube, about 25 centimetres long, that runs from the back of the throat to the stomach.