The pancreas  is the organ that produces the insulin hormone. The pancreas also produces glucagon,  a hormone in opposition to insulin, which forces the release of glucose  into the bloodstream.
Although we focus mainly on its insulin-secreting capabilities, the pancreas is actually comprised of two sections. The endocrine area is connected with natural insulin production. The exocrine  area is connected with production of needed digestive enzymes, and is actually the larger of the two, by far.  Problems with the exocrine section of the pancreas can produce disorders such as pancreatic insufficiency.
The pancreas produces hormones in the islets of Langerhans. Among them, glucagon is produced by the alpha cells, while insulin and amylin are produced in the beta cells. Somatostatin inhibits the release of all three, and is secreted by the delta cells.
Beta cells and insulin productionEdit
Healthy beta cells are constantly making insulin and storing it, as seen in this photo link below.  Those same beta cells release small amounts of insulin day & night, whether the person's eaten or not. This is how the body distributes its natural basal insulin. This is important to the body because it is the basal insulin which allows cells to use blood sugar.
When the insulin level drops, this signals the liver to release glucose by converting stored carbohydrates (glycogen) into glucose for fuel. This release and conversion raises blood glucose levels. It's the body's built in "fail-safe" mechanism to prevent hypoglycemia.
When this occurs, if there are not enough stored carbohydrates in the form of glycogen, the liver will convert protein into glucose in an attempt to keep the body going. If there's not enough carbohydrates or enough protein in the diet, the liver will begin turning body muscle into glucose to keep itself alive.
Glucose  is important enough to the bodies of all mammals that there are 5 different glucose transporters  which carry it to the various body cells. Each of them distribute glucose to a specific area of the body.
Normal insulin secretionEditIn those without diabetes, the healthy pancreas secretes insulin in pulses or spurts. Basal insulin secretion is a series of small pulses or spurts at a given rate day and night; these insulin pulses or spurts are to take care of the body's basic needs. When someone without diabetes eats a meal, the pancreas goes into higher gear, turning out larger quantities of post-prandial insulin to handle the additional glucose created by the food. This phase of insulin secretion is often referred to as the first phase, while the steady, slow basal rate is termed the second phase. 
Dogs who don't have diabetes have a similar insulin secreting pattern to people who don't have diabetes, with the same two phases intended for the same purposes as in humans. 
It is this pattern that diabetics try to mimic as closely as possible; with basal insulin injections for the body's needs without considering food and bolus insulin injections to cover meals replacing the Basal and Postprandial insulin their bodies no longer produce or do not produce in sufficient quantity. 
When there's not enough beta cell insulin production to meet the body's basal needs, it can happen very quickly. The problem is when the beta cells aren't able to produce the needed insulin, the body interprets the low fasting insulin level as a sign the blood glucose levels need to be raised. The liver then dumps a large amount of glucose into the bloodstream, regardless if those levels are high or not. (Human diabetics refer to this as a liver dump.)
The failure of the first phase of insulin discussed above above is what brings about the vicious circle of glucose toxicity, which, in turn, damages even more of the insulin-producing beta cells.
- ↑ Pancreas. Wikipedia.
- ↑ Glucagon. Colorado State University School of Veterinary Medicine.
- ↑ Illustration-How Glucose is Released Into the Body. National Institutes of Health.
- ↑ The Exocrine Pancreas.
- ↑ Human Pancreatic Acinar Cell Carcinoma Case. Harvard University.
- ↑ Healthy Beta Cell--Insulin Granules Shown In Red.
- ↑ Nussey, SS., Whitehead, SA. (2001). Endocrinology-an Integrated Approach-Glucose Turnover. National Institutes of Health (NIH).
- ↑ Nussey, SS., Whitehead, SA. (2001). Endocrinology-an Integrated Approach-Glucose Transporters. National Institutes of Health (NIH).
- ↑ Insulin Release. Wikipedia.
- ↑ Hess, Rebecka S. (May 2008). Managing Diabetes Mellitus in Dogs. DVM 360.
- ↑ White, John R., et. al. (June 2003). Novel insulins and strict glycemic control. Postgraduate Medicine.
- Journal of the Pancreas is free to read and contains many relevant articles on diabetes including feline and canine.
- great tutorial on insulin vs. glucagon Colorado State University School of Veterinary Medicine
- The body's flexible uses of glucose Nussey, S.S., Whitehead,S. A., 2001, National Institutes of Health
- Functional Anatomy of the Endocrine Pancreas Colorado State University School of Veterinary Medicine
- Histiology of the Pancreas--Endocrine & Exocrine Colorado State University School of Veterinary Medicine
- Pancreatic Islet Cells Interactive Map Rnceus.com
By Mousing Over , the various cells of the pancreas and their actions are explained.
- Interactive Pancreatic Beta Cells Tour Rnceus.com
Mouse over the various areas to see how healthy pancreatic beta cells produce insulin.