Diabetes is an illness of which I suspect almost all adults in America are aware. I also suspect that most people know that it has something to do with high blood sugar and that having high blood sugar is a bad thing. Still, I imagine there are a fair few people out there who haven’t really got a lot more understanding of it than that—including some people who have the disease—because they haven’t really had it explained to them in terms they can follow. After all, doctors—of which I am one—don’t often take the time necessary to make sure that their patients fully understand the ins and outs of a disease process. Partly this is because, when one understands something on a very complex level, it seems like it’s going to take serious effort to explain it to someone who doesn’t have the same educational background. However, I think this is a failure of imagination and a bit of mental laziness on our part as doctors. The Nobel-Prize-winning physicist Richard Feynman used to prepare “freshman lectures” about physics subjects when laypeople asked him about topics they didn’t understand. If he found that he couldn’t prepare one, he recognized that failure as an indication that the subject wasn’t well-enough understood!
I just love that philosophy and attitude. So, since Diabetes in general is pretty well understood, I’m going to try to give a “freshman lecture” here on Diabetes.
First off, “Diabetes” is actually only part of the name of the disease we’re going to be discussing. The full name of the disorder is “Diabetes Mellitus” and this diagnosis is then subdivided into Type 1 and Type 2. The term “Mellitus” serves to differentiate the common disease known as Diabetes from the far-more-obscure disorder “Diabetes Insipidus,” which I will not really be discussing here.
You see, the word “Diabetes” is a Late Greek word meaning “excessive discharge of urine.” That’s originally all the word referred to, since that is the most noteworthy presenting problem in both kinds of Diabetes. The meaning of the second words in the disease names is going to gross a few people out, and that’s completely understandable. You see, “Mellitus” means (more or less) sweet-tasting, whereas Insipidus—and this will be obvious when you think about it—means “tasteless”.
Sweet? Tasteless? What is sweet or tasteless?
The answer is: That excessive discharge of urine. Yes, in the old days, one way they used to diagnose things was to taste the urine, and the urine in Diabetes Mellitus tasted sweet. Why? It tasted sweet because it was just full of glucose.
Well, urine is not SUPPOSED to be full of glucose! Nature has designed our bodies to want to hold on to glucose, either so we can use it directly as fuel or convert it into one or another storage form that we can use for energy later. Nature doesn’t deal very kindly with creatures that waste precious energy…when survival is at stake that’s a really bad strategy. So the kidneys ordinarily filter the glucose out of urine before it’s passed to the bladder for elimination. Only when the glucose is quite a bit above normal range is the kidney’s ability to do this overwhelmed, and sugar (glucose) starts to spill into the urine and be wasted.
So, how does the blood sugar get so high? Well, ordinarily, the level of sugar in the blood is pretty tightly controlled, mostly by the actions of two major hormones: glucagon and insulin. Most people who have heard of Diabetes have probably heard of insulin. Insulin is a type of hormone called a peptide, which means it’s a small, clipped version of a protein. It’s produced in the pancreas by a group of specialized cells called beta islet cells in an area called the Islets of Langerhans. The name isn’t really that important, except that things have to be given names so we know what we’re talking about when we’re talking to each other. The cells in the pancreas that make insulin were first described by a scientist named Paul Langerhans, so they got named after him. That’s how it works with a lot of obscure medical terms.
Insulin is secreted (released, in other words) by the islet cells in response to the sensed level of glucose in the blood. The more glucose there is, generally, the more insulin is released. Why is this necessary? Because the cells of the body only take up glucose when they’re stimulated to do so by the action of the hormone insulin. Insulin is, quite literally, the signal that tells cells to activate the machinery they use to take glucose in, after which they can digest it for energy to run their metabolism, or they can store it for burning later. So, when we eat and our digestive systems bring glucose into our blood, the glucose level rises, the islet cells release more insulin and the cells take up more glucose. It’s a good system, and usually it works brilliantly.
Incidentally, glucagon, which I mentioned before, is in a way the opposite of insulin. It is released in response to lower blood sugar, and stimulates the release of glucose from storage or the creation of new glucose by the liver. These two hormones—insulin and glucagon—in a healthy person, work beautifully in counterpoint, and maintain the blood sugar between roughly 60 and 100 milligrams per deciliter at all times. It’s a lot like the cruise control on a car, which applies a little more or less power as needed to keep the speed where you set it. A healthy body has a very tight and responsive glucose cruise control.
Diabetes happens when the insulin system breaks down. There are two main ways that this happens, and there are, therefore two main kinds of Diabetes…very cleverly called Type 1 Diabetes and Type 2 Diabetes.
In Type 1 Diabetes, there is a failure of the beta cells in the Islets of Langerhans…usually caused by some kind of inflammation destroying those cells. When this happens, there is no longer any production of insulin to speak of, and without insulin, the cells of the body don’t take up blood sugar. Without blood sugar, many of the cells of the body cannot get new energy, except by very specialized and limited means that have their own downside to the body when they operate without restraint. A person with Type 1 Diabetes absolutely requires the administration of insulin from an external source. This is usually done by injection into the subcutaneous tissue by a fine needle, generally a number of times a day. Without this treatment, a person with Type 1 Diabetes will not be able to get glucose into their cells. They will lose oodles of glucose in their urine, they will rapidly lose weight and dehydrate (because all that spilled glucose in the urine carries a LOT of water with it), and ultimately they will go into a catastrophic state called “Diabetic ketoacidosis.” I won’t get into the specifics of this right now, but it DOES involve the blood becoming quite a bit too acidic, among other things. None of the effects involved are good for the function of a human body, and unless treated quickly and given replacement insulin, a person in Diabetic ketoacidosis will die.
Wow, that’s pretty scary, isn’t it? Fortunately, nowadays we have a number of different forms of readily available and inexpensive injectable insulin for Type 1 diabetics to use…and there are scientists working all the time on better ways of treating this disorder, including working on developing insulin that can be given without injection and transplantable replacement islet cells. Stem cell research may be able to deliver that last modality in readily workable form, without the worry about tissue rejection, so we should all do everything we can to support such research.
Well, this has already gotten pretty long, so that’s going to be it for the first half of the article. I’m going to continue this discussion, of course, in Part 2 which will, appropriately, start with the subject of Type 2 Diabetes Mellitus.