What Happens In The Dog's Body: Insulin

by Jennifer Coates, DVM

In my last post about xylitol poisoning, I mentioned that dogs respond to high blood xylitol levels with a spike in insulin secretion, which has the result of driving down 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 through which it travels to the rest of the body to have an effect on many different types of cells.

It 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 as 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 usable form. It needs to be broken down into its basic building blocks (e.g., 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 liver and muscle cells) to stop breaking down the molecules that store glucose (glycogen), amino acids (protein), and other nutrients, in essence 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 facilitator of glucose uptake into cells, it’s important to remember that like many hormones, it has a myriad of effects throughout the body.


Jennifer Coates, DVM graduated with honors from the Virginia-Maryland Regional College of Veterinary Medicine in 1999.  In the years since, she has practiced veterinary medicine in Virginia, Wyoming, and Colorado.  She is the author of several books about veterinary medicine and animal care, including the Dictionary of Veterinary Terms: Vet-speak Deciphered for the Non-veterinarian

Dr. Coates has recently joined the PetMD team and she is now writing for the Fully Vetted column; great blog, do check it out.

Jennifer also writes short stories that focus on the strength and importance of the human-animal bond and freelance articles relating to a variety of animal care and veterinary topics.  Dr. Coates lives in Fort Collins, Colorado with her husband, daughter, and pets.

Articles by Dr. Coates:
Kidney Disease – Say What? 
What Happens In The Dog's Body When The Kidneys Fail To Function Properly? 
Heat Stroke: What Happens In The Dog's Body?  
The Perplexities of Pancreatitis
The Other Side Of The Coin: The Cost Of Defensive Medicine
To Neuter Or Not To Neuter… That Is The Question
Don’t Forget the Physical Therapy
Common Misdiagnoses (Part 1)
Common Misdiagnoses (Part 2)
Picking the Right Dog to Breed
When Is It An Emergency?
Dog Allergies: Common, Commonly Misdiagnosed, or Both? 
Why Does The Spleen Get No Respect?
Protect Your Dog From Snake Bites 
More Creepy Crawlies
Why I Dislike Inflammatory Bowel Disease
Salmonella – A Significant Problem, Or Not? 
What’s In the Vomit?
Cortisol: What Happens In A Dog’s Body When It Goes Awry?
What Happens In The Dog's Body With Zinc Toxicity? 
What Happens In The Dog’s Body: Xylitol Poisoning