So, diabetes is a very common disease. It affects nearly 10percent of the population and more than 25 percent,or one in four people over the age of 65 have diabetes. But what exactly is diabetes mellitus? Let me start by going througha couple of scenarios. Now the first scenario I wanna talk about is that of Joe here. So let me bring in Joe. Now Joe is a 15 year old boy.
Over the past few months Joe just really hasn’t been feeling well. He says, you know it’s hard to kind of put his finger on it, but he’s in general been a little bit more tired and fatigued than usual. In fact, it’s caused him tolose a little bit of weight and he’s already kind of askinny guy to begin with, so that’s definitely somethingthat’s abnormal for him. And you know his mother’swith him and his mother says you know “Joe’s been, it’s kinda been odd, “Joe’s been carryingaround this water bottle “with him everywherefor the past few months. “He seems to just be drinking “liters upon liters of water a day.” And when asked about itJoe acknowledges this, he says “Yeah, I have been a little bit “more thirsty than usual.”and because of this, he says, “You know, I’ve been going to bathroom, “I’ve been needing tourinate all the time.” Now, let’s contrast Joe to Bruce here. Now, Bruce is very different than Joe. Bruce is a 45 year old gentleman. And he’s come in to the doctor for his annual physical andwhen he goes to the doctor he says, “You know doc, I’vebeen feeling pretty good. “I mean, yeah, maybe I’ve packed on “a few extra pounds around the waist, “but in general I’mfeeling pretty healthy.” Now, say both Joe over here and Bruce are seeing the samefamily practice doctor.
You know for Joe, hesays “Yeah, I am worried “about this thirst andurination and the losing weight. “I think we should probablycheck Joe’s blood sugar.” And then similarly with Bruce, even though he doesn’t have any symptoms,the doctor recommends that Bruce has some routine screening done that would includechecking his blood sugar. And it turns out that both Joe and Bruce have very high blood sugar. They have something called hyperglycemia, which stands for high blood sugar. And they’re both diagnosed with diabetes. But how can such differentsituations with Joe and Bruce be caused by the same disease? Now, to answer this question, we first, really need to understandwhat exactly, diabetes is. Now the first thing I wanna mention is that I’ve been referringto diabetes mellitus and there are a coupledifferent conditions that have the word diabetes in them. But generally whenpeople refer to diabetes, they’re referring to thedisease diabetes mellitus, which is what we’regonna be talking about. So diabetes mellitus is agroup of disorders that are characterized by an inability of the body to regulate its blood sugar levels. And you’ll notice that I putglucose here in parenthesis after sugar, because glucoseis the main type of sugar that the body uses. And this disregulationresults in high blood sugar, or hyperglycemia. So, to get a better idea ofthis, let me just bring in a simple diagram here.
So this right here in pink, imagine this is a blood vesseland in this blood vessel there is blood going through. And that blood has glucose. Now, glucose is a sugarand it’s the body’s preferred source of energy. And we get glucose fromthe foods that we eat, and then the glucose that we eat is stored throughout the body, but primarily in the liver here. And to regulate the amountof sugar that is in our blood we have two hormones. The first hormone I’ll haveover here in orange is insulin. And then the second hormoneI’ll have over here in blue is glucagon. And then down here in green is a cartoon of some cells in the body that are gonna needthis glucose for energy. When the glucose level in theblood is getting too high, the pancreas releases this insulin. And what the insulin does is it stops the release of glucose from the liver into theblood and then it also has this glucose be taken up by the cells. And so this decrease inthe amount of glucose being put into the blood from the liver and then the increase amount of glucose leaving the blood going into these cells causes that blood sugar level to go down. So insulin decreases blood sugar. But if insulin were tojust act on it’s own, the blood sugar wouldbe always way too low, so when that blood sugar startsgetting to a lower level, the pancreas then will release glucagon. And what glucagon doesis it causes the liver to release that glucose into the blood, all that glucose that’s stored there. And then it also causes the pancreas to stop producing theinsulin so that less glucose is being taken out of theblood and put into cells. And therefore then, the effect of this by having the liver putglucose into the blood and then preventing theglucose from leaving the blood, glucagon results in anincreased blood glucose level. So now, in diabetes, this insulin here is either not being produced or it’s not functioning properly. So let’s just cross it out. It’s not doing its job.
And what happens is thatthe effect of glucagon here is amplified. So you get this increasein blood glucose levels. And then as I mentioned, insulin causes glucose to exit the bloodand go into the cells so that the cells can usethe glucose for energy. But if it’s not around,this doesn’t happen. So despite the blood sugar, the blood glucose level isgetting higher and higher, that glucose isn’t ableto get into the cells. And the body isn’t ableto use all of that energy. So in a sense, despite the presence of plenty of blood sugar and energy, the cells are actually kind of starving. And that’s actually what can go on. You can have this reallyhigh blood sugar level, but the body in some sensesthinks it’s starving. And this idea of kind of starvation in the face of plenty of energyis a little bit confusing. So let me just make an analogy here to hopefully have it make more sense. So it’s very similar here.
Now imagine instead ofthis pink blood vessel, imagine this is a water main. Now, the purpose of that water main is to bring water to these houses. Now, imagine that one of these pipes that went from the water mainto the house gets clogged. Now, despite plenty of water being travelling down the street and being right by the house, the house actually isn’table to get any water. And this is kind oflike that same idea of, despite all of the glucosebeing in the blood, when you don’t have insulin, you can’t get the glucose into the cells. Just like if you have a cloggedpipe that prevents water from coming from thewater main into a house. So now let’s go back to Joe and Bruce and understand how youcan have the same disease that causes such different presentations in different people.
Remember I said that diabetes mellitus is a group of diseases. They’re not all the same disease. So, depending on the underliningmechanism that’s going on, the disease can present in very ways. So Joe over here on the left, he is a very typicalpresentation of type 1 diabetes. And I’m gonna just abbreviate diabetes, DM, for diabetes mellitus. And in type 1 diabetes, Joe’s body isn’t producing any insulin. And that results in that high blood sugar. But over here with Bruce, he has a different underlying mechanism. His presentation is very characteristic for something called type 2 diabetes.
And in type 2 diabetes,the body produces insulin, but the receptors on the cells are not as sensitive to insulin, so insulin just doesn’t functionlike it’s normally able to. And so it has a verydifferent presentation. Even though for both of them, insulin is not working properly and it results in hyperglycemia, which is the characteristicfinding in diabetes, depending on the underlying mechanism, whether or not you arenot producing insulin or whether the insulin justisn’t working properly, you still have hyperglycemia but the presentationscan be very different.