Pancreas: Tissue Function

Development of the Pancreas

Two buds appear on the dorsal and ventral sides of the foregut near the anterior intestinal portal during the fourth week of gestation. These buds initially grow and differentiate separately but eventually fuse to form the pancreas. The head, body, and tail of the pancreas develop from the dorsal bud, while the ventral bud gives rise to a part of the head region of the pancreas. The two independently growing pancreatic buds contain their own ducts but after they fuse to form the mature pancreas, these ducts join to form the main pancreatic duct. The endocrine cells of the pancreas are thought to develop from the neural crest. The transcription factors Pdx1, HB9, and p48-Prf1a have been shown to be important for the development of the pancreas. During early pancreatic development, the mesenchymal cells proliferate at a faster rate than the epithelial cells, while later in the developmental process the epithelial cells outgrow the mesenchymal cells. Differentiation of the pancreatic epithelial cells into endocrine cells occurs at 12 weeks of gestation, and around 16 weeks of gestation, the differentiation of the acinar cells is observed. Evidences suggest that Wnt signaling is probably important for the differentiation and maturation of the various cells types in the pancreas. It is also speculated that the adult mature pancreas contains multipotent progenitors or stem cells and that Notch1 signaling promotes the proliferation and survival of these stem cells.

By the end of the fourth month of gestation, the presence of digestive enzymes in the pancreas can be detected. However, the relative amounts and activities of the various digestive enzymes are different during the gestational period as well as at birth compared to those in an adult pancreas. The endocrine function of the pancreas parallels that of its exocrine function. Therefore, the pancreas of newborns and infants is slower to respond to high glucose levels in the blood than that in an adult. However, after birth, with differences in the food that is fed to an infant, the response time of the pancreas to secrete hormones to maintain a stable glucose concentration in the blood gets shortened very quickly.

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