Human Anatomy - H. I. Koliadenko 2009

The Doctrine of Visكera (Splanchnology)
Development of the digestive system. Ontogeny and phylogeny

During the third week of embryonic development, the gut endoderm forms a blind-ended primary tube anterior to the notochord. By the end of the first month, the anterior end of the tube connects with the primitive Oral Cavity, rupturing to mark the beginning of oral cavity development. The posterior end of the tube opens into the endodermal anal pit, which gives rise to the lower part of the rectum. The intestinal tube consists of two regions: the HEAD and trunk gut. The head gut comprises the oral and pharyngeal parts, while the trunk gut is subdivided into the foregut, midgut, and hindgut.

The oral cavity develops from the oral segment of the gut, which is lined with epithelium of ectodermal origin. The pharyngeal gut, lined with endodermal epithelium, gives rise to the oral cavity proper and the Pharynx. Outpouchings known as five pharyngeal pouches form from the pharyngeal gut, separated by two visceral arches (the mandibular and hyoid) and three branchial arches. In fish, branchial clefts with branchial arches between them develop at the junction of the pharyngeal pouches and branchial grooves.

In higher vertebrates, visceral arches appear and pouches are laid down, but only the first cleft actually forms; it later develops into the Middle ear cavity, the auditory tube, and the external acoustic meatus.

The foregut gives rise to the Esophagus, Stomach, and duodenum. The midgut forms the Small Intestine and part of the Large Intestine—specifically the cecum, ascending colon, and transverse colon—as well as The Liver and Pancreas. The hindgut develops into the descending colon, sigmoid colon, and rectum.

In a newborn infant During the first months of life, the pancreas weighs only 2–3.5 g, yet the number of internal secretion islets is substantial, reaching 100,000–120,000.