Analogy: Consider the case of a poor gold processing plant (the pancreas). It has tremendous capacity, works perfectly, and at a magically high rate of speed. In fact, the plant has multiple crushers and smelters (B Cells) inside it. The gold processing plant is fed by trucks bearing ore (glucogan in the blood). The trucks run on an 6-lane one-way highway (artery). Sometimes there are only a few trucks on the road, sometimes hundreds.One day, a landslide (partial arterial blockage due to arterial twist perhaps) shuts down 5 lanes on the highway. Now, despite the ability of the gold processing plant to refine gold at a high rate of speed, its output is severely limited because it can only refine at the rate the gold ore comes in. At times of the day when traffic is light, the gold processing plant kicks out gold at the same rate as before. When there are a lot of trucks on the road, production only increases a little bit because the amount of ore coming in is limited by the bottleneck in the road.
The B cells in the Islets of Langerhans in the Pancreas make insulin from nutrients in the blood. I'd like to say, "from glucogan" but I've lost the quote. All I can find now is that they make insulin from pro-insulin, and pro-insulin from pre-pro-insulin (his favorite protein). Pre-pro-insulin has the same elements in it as glucogan. But whatever, something traveling in the blood is used by the pancreas to make insulin. Note well: the B cells not only sense an increased level of glucogan in the blood and make insulin, which they would presumably do whether the blood supply was diminished or not, they make insulin from something in the blood. If there is less blood coming in, and hence less raw material available, less insulin can be made in a given time period. A strangled pancreas makes this likely.
(The pressure put on the pancreas need not be directly due to compression. It need not be that fat pushes on the duodenum and the duodenum crushes the pancreas. It may be more like one end of a string is tied to the stomach, the other end is tied to the ligament of treitz, and fat pushes the stomach over which tightens the loop. Perhaps the ligament of treitz plays no roll. Perhaps the fact the duodenum is attached to the right abdominal wall and the stomach attached to the left abdominal wall is what's doing it. As the two stretch apart due to fat increasing the space (like an inflating balloon), the superior pancreaticoduodenal artery gets yanked and twisted near where the stomach intersects the duodenum. See my "Anatomy of a Strangle" entry, above.)
