Development of pancreas and liver

The liver and pancreas both originate from the foregut’s endoderm, with the liver developing from the hepatic diverticulum and the pancreas from the dorsal and ventral pancreatic buds. These organs undergo significant morphogenetic changes and fusion to form their mature structures, and they both play essential roles in digestion and metabolism by the end of embryonic development.

Pancreas

Development of Pancreatic and Liver Bud, Langmans

The pancreas develops from two distinct buds: the dorsal pancreatic bud and the ventral pancreatic bud, both of which arise from the endodermal lining of the foregut. The dorsal bud forms the body and tail of the pancreas, while the ventral bud forms the uncinate process and part of the head. During the 5th week, the ventral pancreatic bud rotates and fuses with the dorsal bud as the foregut undergoes rotation. This fusion gives rise to the mature pancreas, with the dorsal part contributing to the main body and tail and the ventral part contributing to the head and uncinate process. The pancreas becomes functional by the 12th week, with its endocrine component (the islets of Langerhans) developing from clusters of endodermal cells and its exocrine component (the acinar cells) developing from the surrounding endoderm. The pancreatic ducts form from the ducts of both pancreatic buds, connecting the pancreas to the duodenum.

Liver

The liver begins as a ventral outgrowth from the foregut called the hepatic diverticulum or liver bud around the 3rd week of embryonic development. This diverticulum arises from the endoderm of the duodenum and extends into the surrounding mesoderm, forming the liver. As the liver bud grows, it divides into two main parts: the larger left lobe and the smaller right lobe, which later fuse. The mesoderm surrounding the liver bud gives rise to the hepatic sinusoids and blood vessels, while the endoderm forms the hepatocytes and biliary tree (gallbladder and bile ducts). By the 6th week, the liver starts to function in hematopoiesis, and by the 12th week, it takes on its metabolic roles, including bile production. The gallbladder also forms as a distinct outpouching from the liver bud, while the bile duct connects the liver to the duodenum.

References

Langman's Medical Embryology, 14th Edition, by T.W. Sadler: Chapter on the development of the liver and pancreas.

The Developing Human: Clinically Oriented Embryology, 10th Edition, by Moore et al.: Detailed sections on the liver and pancreas development.