Corpus: Foregut

In embryology, the term foregut refers to the anteriormost, cranial section of the primitive embryonic intestinal tube. It lies between the oral cavity and the midgut.

The foregut is bounded at its cranial end by the prechordal plate. It ends there blindly at the oropharyngeal membrane.

The foregut can be divided into two sections:

• upper foregut (embryonic pharynx)
• lower foregut (oesophagus, stomach and upper part of the duodenum)

In addition, the trachea and lungs also develop by sprouting from the foregut. Some authors also use the term "head intestine" for the upper foregut.

• Oesophagus: Initially it is only present as a short epithelial tube, which subsequently lengthens by stretching the upper half of the body and the descent of the thoracic viscera. The mesenchyme surrounding the epithelial tube forms 2 layers of smooth muscle. The oesophagotracheal septum forms the boundary to the trachea.

• Stomach: The gastric anlage is initially a spindle-shaped extension that is held to the right and left of the ventral mesogastrium. The posterior wall of the anlage grows faster than the anterior wall. This results in the formation of the small and large gastric curvature. This is followed by the 1st rotation of the stomach around the longitudinal axis (90° clockwise). This is followed by the 2nd rotation of the stomach ("stomach tilt") around the sagittal axis, which causes the cardia to shift to the left and minimally downwards and the pylorus to the upper right. Both the right and left vagus nerves are also displaced by rotation and tilting. The left vagus nerve is now ventral and forms the anterior vagal truncus, the right one is now dorsal and forms the posterior vagal truncus.