Surgical Anatomy

Abstract

The oesophagus arises from the primitive foregut. It commences as a short tube which extends from the tracheal groove above to the fusiform dilatation of the foregut below, which 20 days after fertilisation will develop into the stomach. An external ridge develops on the 23rd day on its anterior wall and deep to this an internal groove, the laryngo-tracheal sulcus, forms which gradually extends caudally. This groove deepens and is pinched off by lateral ridges to form a tube situated ventral to the oesophagus. The tube later widens to form the bilobed lung bud. By the 36th day separation of the two tubes is complete. The primitive oesophagus lies on the posterior aspect of the septum transversum and is embedded in visceral mesoderm. The oesophagus rapidly lengthens during the sixth and seventh weeks as the larynx ascends and the heart and lung buds descend. During this time the oesophagus temporarily becomes obliterated due to its elongation and also because of a proliferation of the endodermal lining cells. Recanalisation of the oesophagus gradually occurs and the lining epithelium changes to a stratified squamous type, possibly as a result of metaplasia and possibly due to migration of cells from the oral cavity. Foci of columnar cells may persist, however, and this may explain the occasional development of an adenocarcinoma of the oesophagus. The visceral mesoderm differentiates into muscular and connective tissue layers between the 6th and 12th week. The left and right gastric nerves come to lie anterior and posterior to the oesophagus as the stomach rotates to the right.