I saw an adult patient this week who I diagnosed with diabetes mellitus. Everyone has heard of diabetes, but what is it really?

Diabetes was first described in Egypt about 3,500 years ago. One translation of diabetes is "to pass through," referring to the frequent urination that occurs in diabetics. The urine also contains glucose, a sugar, hence the name mellitus which means honey in Latin. In fact, many physicians in years past diagnosed the disease by watching the affinity of insects, particularly ants, to a patient's urine. Some bold physicians even went so far as to do a little taste test (thank goodness for the development of the urine dipstick)!

To understand diabetes, I have to explain how the body uses glucose, the main sugar the body uses for energy. When we digest sugars and starches, they are broken down into simple sugars, one of which is glucose. The glucose is absorbed by the intestine and travels via the blood vessels to all of our cells.

The hormone insulin is required for glucose to enter our cells where it is used for energy. Insulin is produced by the pancreas, an organ that sits behind the stomach in the upper abdomen. The insulin molecule is analogous to a key that has to fit in the lock of a gate. Just as a key turns tumblers in a lock, the insulin binds to its receptor on the membranes of cells and initiates biochemical interactions that open "gates" on the cells, allowing glucose to enter.

Diabetes develops when the key and/or the lock is not working properly. Since the glucose can't enter the cells, its level rises in the bloodstream. This can lead to a number of problems. Glucose passes through the kidneys, taking water with it, causing the diabetic patient to urinate frequently. The excess urination leads to dehydration and excessive thirst.

The glucose in the blood stream can also be toxic to many tissues resulting in, among other things, an increased risk of cardiovascular disease, kidney disease, and nerve damage. Diabetes is still the leading cause of blindness in the world.

There are two types of diabetes, Type I and Type II. Type I, formerly referred to as juvenile onset diabetes, accounts for about ten percent of diabetes and is the result of a lack of insulin production (no key for the lock). Although more common in young people, it can happen at any age, hence the name change to Type I.

Type I diabetes is usually caused by antibodies that kill the pancreatic cells that produce insulin. It's not known why this happens though many theories point to a possible viral trigger as well as genetic factors.

When cells can't get enough glucose, they essentially starve. This causes the cells to switch to using fat for energy. Burning fat leads to another common sign of Type I diabetes - weight loss. The problem when turning to fat for energy is that it produces fuel sources that are quite acidic and can lead to a condition called diabetic ketoacidosis. The acidity, along with very high glucose levels, leads to all kinds of nasty chemical reactions that can be fatal.

Type II is the other type of diabetes. This was formerly known as adult onset diabetes and is far and away the most common type. It is seen primarily in obese adults, though obesity is not a prerequisite. The incidence of Type II diabetes is exploding in all age groups and sadly, is becoming more common in obese children.

Type II diabetics may have reduced insulin production, but their primary problem is "insulin resistance," which means their cells are resistant to the effect of insulin. They produce the keys to the locks, but the tumblers don't work correctly so the gates don't open.

The glucose levels in these patients do not get as high as in Type I diabetics and they do not develop ketoacidosis. Despite this, they still develop all the terrible illnesses associated with diabetes. Since it is appearing at younger ages, we are seeing teenagers with advanced cardiovascular and kidney disease.

Next week I'll explore the diagnosis and treatment of diabetes.

Dr. John Roberts is a Crawfordsville physician and one of the owners of The Paper. In addition to his weekly column, he writes a daily health tip that can be found on page A1.