This is my fanciful drawing and simplified explanation of how diabetes affects your dog.

Two compounds are involved, the Glucose molecule (drawn to the far upper left) and the much larger insulin molecule next to it. Both compounds circulate freely in your pet’s blood. The glucose came from the foods your dog ate or was produced in its liver from stored carbohydrates (glycogen) and proteins. The insulin molecules were produced in its pancreas.

Glucose is the primary energy source for the estimated 5-50 trillion cells that compose your dog’s body.

At the upper right is a fanciful image of one of those cells. Glucose molecules can not pass into these cells without the aid of insulin. And in Type I diabetes, there is much less insulin around. Once inside the cells, the glucose is taken up by the cells many or single mitochondria (aka mitrochonrion), represented as oval yellow bodies with honeycomb compartments.

Your dog's mitochondria function as microscopic “power plants” generating the chemical energy all cells need - much of it by “burning: (oxidizing) glucose.

In the lower right of the illustration, I drew the dog's liver and intestines, with the pet’s pinkish pancreas snuggled between loops of its small intestine. Within its pancreas are many small island, the islets of Langerhans. These are the portions of your dog’s pancreas that secrete insulin.

The microscopic view of these island-areas that I drew, shows one with a normal functioning islet and another, to the left of it, in which the islet is no longer producing insulin. Chronic inflammation has replaced the dog's ß-cells with scar tissue.