Pancreatic regional blood flow links the endocrine and exocrine diseases

An increasing number of studies have demonstrated that disease states of the endocrine or exocrine pancreas aggravate one another, which implies bidirectional blood flow between islets and exocrine cells. However, this is inconsistent with the current model of unidirectional blood flow, which is strictly from islets to exocrine tissues. This conventional model was first proposed in 1932, and it has never to our knowledge been revisited to date. Here, large-scale image capture was used to examine the spatial relationship between islets and blood vessels in the following species: human, monkey, pig, rabbit, ferret, and mouse. While some arterioles passed by or traveled through islets, the majority of islets had no association with them. Islets with direct contact with the arteriole were significantly larger in size and fewer in number than those without contact. Unique to the pancreas, capillaries directly branched out from the arterioles and have been labeled as “small arterioles” in past studies. Overall, the arterioles emerged to feed the pancreas regionally, not specifically targeting individual islets. Vascularizing the pancreas in this way may allow an entire downstream region of islets and acinar cells to be simultaneously exposed to changes in the blood levels of glucose, hormones, and other circulating factors.