What is Diabetes Mellitus?

Diabetes mellitus is a chronic disorder of carbohydrate metabolism. There are 2 types of diabetes mellitus. Insulin-dependent diabetes mellitus, or type 1, is a true lack of the hormone insulin in the body. Non-insulin-dependent diabetes mellitus, or type 2, is an inability of the cells to respond to the insulin.

Insulin is produced in the pancreas by cells called islet cells. Insulin works with another hormone called glucagon, also produced in the pancreas, to regulate production and removal of blood sugar (glucose) from the circulating blood. Glucose is the primary source of energy for most of the cells in the body, especially the brain. Insulin attaches to receptors on cells throughout the body that control and allow glucose to enter the cells.

When more insulin is present, blood sugar levels decrease due to more absorption by cells. Insulin production can be stimulated by increased blood glucose levels and increased demand for glucose by the body’s cells. Cellular insulin receptor numbers are also increase by greater cell demand for energy.

When more glucagon is present, more glucose is produced and released into the blood. Glucagon production is stimulated by decreased blood glucose levels. The absolute amounts and the ratio of insulin to glucagon are important for maintaining the closely regulated blood glucose level.

In type 1 diabetes mellitus, the pancreas is not able to produce insulin. Therefore, the body’s cells are not able to absorb the glucose in the blood. This leads to dramatically increased blood glucose levels.

In type 2 diabetes mellitus, insulin may be present in high, normal or low amounts, but the cells are not able to make use of the insulin due to a decrease in the number of cellular receptors. Therefore, the cells cannot absorb the glucose and the blood glucose levels increase.

Dogs typically present with type 1 diabetes. This may be secondary to an immune mediated destruction of the islet cells. Most of the time, the underlying cause is not identified. Occasionally diabetes develops after pancreatitis, an inflammation of the pancreas. In humans, this form has been referred to as juvenile onset diabetes. In general, dogs are very glucose resistant and do not develop type 2 diabetes.

Cats typically present with type 2 diabetes. Most cats with diabetes are middle aged to older and overweight, at least at the onset of symptoms. Most of these cats have sedentary lifestyles. Cats are not glucose resistant like dogs. This type of diabetes mellitus is commonly seen in overweight humans. However, when most cats are diagnosed, they have become insulin dependent.

Type 1 and type 2 diabetes mellitus present with similar symptoms. Most commonly, owners report dramatically increased thirst and urination, and weight loss. The animals often have decreased activity levels, and sometimes changes in behavior. Some animals will present with a severe, life threatening diabetic crisis referred to as diabetic ketoacidosis (DKA).

Glucose normally passes into the urine and then gets reabsorbed by the kidneys and returned to the blood. High blood glucose levels exceed the ability of the kidneys to reabsorb the glucose. Glucose attracts water, so the water molecules are also not reabsorbed by the kidneys. Thus, the urine production increases. Water intake must increase to maintain normal hydration. The glucose passed in the urine represents a very large amount of energy lost. Therefore, weight loss is difficult to avoid.

With diabetes, the body tries to provide energy to the cells, but the cells cannot make use of that energy. The body must compensate for its negative energy flow. Therefore, it mobilizes fat. Many of the cells in the body, including the brain, are able to make use of the fat as energy when given a little time to convert. However, glucose still represents the preferred energy source.

The mobilization of the fat produces many waste products the body can get overwhelmed with. When one type of these waste products, called ketone bodies, build up, their acidic nature causes severe metabolic derangements throughout the body producing DKA. Diabetics in DKA typically present vomiting, severely dehydrated, very depressed, sometimes comatose, and very weak. Patients with DKA are critically ill and will die without very aggressive emergency treatment.

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