In my last post about xylitol poisoning, I mentioned that dogs respond to high blood xylitol levels with a spike in insulin secretion. This spike results in a dramatic drop in blood sugar levels.
I thought this was the perfect opportunity to delve into how insulin works.
Insulin is a hormone.
It is produced by beta cells within the pancreas and secreted into the bloodstream. That is how insulin travels to the rest of the body to affect many different types of cells.
Insulin can also be manufactured as a drug to be given by injection when dogs
- either don’t produce enough insulin on their own (Type I Diabetes), or
- need more insulin than normal because their bodies have become resistant to it (Type II Diabetes).
Most dogs have Type I Diabetes. Type I Diabetes is a result of an autoimmune reaction that is directed against and destroys their beta cells. In contrast, most cats have Type II Diabetes, which is often related to obesity.
Regardless of whether insulin is secreted naturally or given as a drug, it has the same primary job – driving glucose out of the bloodstream and into cells where it can be used for energy.
But that’s not all insulin does.
To explain, I’ll start at the beginning… a dog has just eaten a meal.
The food that has entered the dog’s digestive tract is really not in a usable form. It needs to be broken down into its basic building blocks
- proteins into amino acids
- complex carbohydrates into simple sugars, etc..
That’s what the gastrointestinal tract does–turning steak, for instance, into a soup of amino acids (and other things) that can be absorbed through the intestinal wall into the bloodstream.
The presence of glucose, amino acids, etc. in the small intestine is the signal the pancreas needs to secrete insulin.
The pancreas “knows” that the bloodstream is about to be inundated so it sends in the troops (insulin) to deal with it.
Nutrients in the bloodstream don’t do the body much good.
They need to make it into appropriate cells where they can either be
- “burned” for energy, or
- used as building blocks for the more complex molecules the body needs
Insulin is like a key that unlocks the door allowing these nutrients to enter cells.
At the same time, insulin signals the rest of the body (primarily the liver and muscle cells) to stop breaking down the molecules that store glucose (glycogen), amino acids (protein), and other nutrients. In essence, it is saying, “slow down, we’ve got enough here for the moment.
The reverse is also true; insulin sends the signal to the body to start making glycogen out of glucose, protein out of amino acids, and fat out of fatty acids.
If you’re interested in more detail, check out these lecture notes. I particularly liked the following diagram:
Even though we often think of insulin strictly in its role as a facilitator of glucose uptake into cells, it’s important to remember that like many hormones, it has a myriad of effects throughout the body.
Xylitol Poisoning in Dogs