Pancreas

The pancreas is formed by two buds originating from the endodermal lining of the duodenum (Fig. 13.21). Whereas the dorsal pancreatic bud is in the dorsal mesentery, the ventral pancreatic bud is close to the bile duct (Fig. 13.21). When the duodenum rotates to the right and becomes C-shaped, the ventral

Pancreatic Bud

Figure 13.22 A. Pancreas during the sixth week of development. The ventral pancreatic bud is in close contact with the dorsal pancreatic bud. B. Fusion of the pancreatic ducts. The main pancreatic duct enters the duodenum in combination with the bile duct at the major papilla. The accessory pancreatic duct (when present) enters the duodenum at the minor papilla.

Figure 13.22 A. Pancreas during the sixth week of development. The ventral pancreatic bud is in close contact with the dorsal pancreatic bud. B. Fusion of the pancreatic ducts. The main pancreatic duct enters the duodenum in combination with the bile duct at the major papilla. The accessory pancreatic duct (when present) enters the duodenum at the minor papilla.

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Annular Pancreas Image

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Figure 13.23 Annular pancreas. The ventral pancreas splits and forms a ring around the duodenum, occasionally resulting in duodenal stenosis.

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Figure 13.23 Annular pancreas. The ventral pancreas splits and forms a ring around the duodenum, occasionally resulting in duodenal stenosis.

pancreatic bud moves dorsally in a manner similar to the shifting of the entrance of the bile duct (Fig. 13.21). Finally the ventral bud comes to lie immediately below and behind the dorsal bud (Fig. 13.22). Later the parenchyma and the duct systems of the dorsal and ventral pancreatic buds fuse (Fig. 13.22B). The ventral bud forms the uncinate process and inferior part of the head of the pancreas. The remaining part of the gland is derived from the dorsal bud. The main pancreatic duct (of Wirsung) is formed by the distal part of the dorsal pancreatic duct and the entire ventral pancreatic duct (Fig. 13.22B). The proximal part of the dorsal pancreatic duct either is obliterated or persists as a small channel, the accessory pancreatic duct (of Santorini). The main pancreatic duct, together with the bile duct, enters the duodenum at the site of the major papilla; the entrance of the accessory duct (when present) is at the site of the minor papilla. In about 10% of cases the duct system fails to fuse, and the original double system persists.

In the third month of fetal life, pancreatic islets (of Langerhans) develop from the parenchymatous pancreatic tissue and scatter throughout the pancreas. Insulin secretion begins at approximately the fifth month. Glucagon- and somatostatin-secreting cells also develop from parenchymal cells. Splanchnic mesoderm surrounding the pancreatic buds forms the pancreatic connective tissue.

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