Source: http://www.niddk.nih.gov/health/pancreatic/stem/agenda.htm
The human pancreas is composed of the following cell types: the ductal cells, the endocrine cells, and the acinar cells. The ductal cells are from the pancreatic ducts, and connect the acinar cells to the digestive organs. The endocrine cells produce the following hormones: glucagon, insulin, and pancreatic polypeptide. These hormones are secreted into the bloodstream, where they assist the body in sugar metabolism. The acinar cells manufacture digestive enzymes.
Human embryonic pancreatic development begins as an outgrowth of the duodenum, which is part of the small intestine. At the foregut/midgut junction, the septum transversum generates two pancreatic buds called the dorsal and ventral endoderm. These two patches fuse to form the pancreas. The dorsal bud arises first and generates most of the pancreas. The ventral bud arises beside the bile duct and forms only part of the head and uncinate process of the pancreas.
Source: http://anatomy.med.unsw.edu.au/cbl/embryo/Notes/git9.htm
At the cellular level, the acinar cells and the islet cells seem to both originate from the ductal cells during development. These cells emerge from the pancreatic ducts to form aggregates that are later identified as Islets of Langerhams.
During fetal development, new endocrine cells seem to be generated from progenitor cells in the pancreatic ducts. Some researchers claim that islet stem cells can be found intermingled with ductal cells during fetal development and that those stem cells differentiate into new endocrine cells during fetal development. Ductal cells are later identified and distinguished from endocrine cells by their structure and by the genes they express. Specifically, ductal cells express a gene called cytokeratin-9, which codes for a structural protein.
Following birth and into adulthood, the source of islet cell production is not well known. There is some controversy as to whether or not adult stem cells are present in the pancreas. Some researchers claim that islet stem cells can be found in the pancreatic ducts or in the islet cells themselves. Others claim that ductal cells are capable of differentiating into islet precursor cells. Another opinion is that new islet cells arise from stem cells in the blood [22].
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