So, diabetes is a very common disease. It affects nearly 10
percent 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 through
a 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 to
lose a little bit of weight and he's already kind of a
skinny guy to begin with, so that's definitely something
that's abnormal for him. And you know his mother's
with him and his mother says you know "Joe's been, it's kinda been odd, "Joe's been carrying
around this water bottle "with him everywhere
for the past few months. "He seems to just be drinking "liters upon liters of water a day." And when asked about it
Joe 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 to
urinate 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 and
when he goes to the doctor he says, "You know doc, I've
been feeling pretty good. "I mean, yeah, maybe I've packed on "a few extra pounds around the waist, "but in general I'm
feeling pretty healthy." Now, say both Joe over here and Bruce are seeing the same
family practice doctor. You know for Joe, he
says "Yeah, I am worried "about this thirst and
urination and the losing weight. "I think we should probably
check 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 include
checking 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 different
situations with Joe and Bruce be caused by the same disease? Now, to answer this question, we first, really need to understand
what exactly, diabetes is. Now the first thing I wanna mention is that I've been referring
to diabetes mellitus and there are a couple
different conditions that have the word diabetes in them. But generally when
people refer to diabetes, they're referring to the
disease diabetes mellitus, which is what we're
gonna be talking about. So diabetes mellitus is a
group of disorders that are characterized by an inability of the body to regulate its blood sugar levels. And you'll notice that I put
glucose here in parenthesis after sugar, because glucose
is the main type of sugar that the body uses. And this disregulation
results in high blood sugar, or hyperglycemia. So, to get a better idea of
this, let me just bring in a simple diagram here. So this right here in pink, imagine this is a blood vessel
and in this blood vessel there is blood going through. And that blood has glucose. Now, glucose is a sugar
and it's the body's preferred source of energy. And we get glucose from
the 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 amount
of sugar that is in our blood we have two hormones. The first hormone I'll have
over here in orange is insulin. And then the second hormone
I'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 need
this glucose for energy. When the glucose level in the
blood 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 the
blood and then it also has this glucose be taken up by the cells. And so this decrease in
the 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 to
just act on it's own, the blood sugar would
be always way too low, so when that blood sugar starts
getting to a lower level, the pancreas then will release glucagon. And what glucagon does
is 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 the
insulin so that less glucose is being taken out of the
blood and put into cells. And therefore then, the effect of this by having the liver put
glucose into the blood and then preventing the
glucose from leaving the blood, glucagon results in an
increased 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 that
the effect of glucagon here is amplified. So you get this increase
in blood glucose levels. And then as I mentioned, insulin causes glucose to exit the blood
and go into the cells so that the cells can use
the glucose for energy. But if it's not around,
this doesn't happen. So despite the blood sugar, the blood glucose level is
getting higher and higher, that glucose isn't able
to get into the cells. And the body isn't able
to 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 really
high blood sugar level, but the body in some senses
thinks it's starving. And this idea of kind of starvation in the face of plenty of energy
is 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 of
this 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 main
to the house gets clogged. Now, despite plenty of water being travelling down the street and being right by the house, the house actually isn't
able to get any water. And this is kind of
like that same idea of, despite all of the glucose
being in the blood, when you don't have insulin, you can't get the glucose into the cells. Just like if you have a clogged
pipe that prevents water from coming from the
water main into a house. So now let's go back to Joe and Bruce and understand how you
can 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 underlining
mechanism that's going on, the disease can present in very ways. So Joe over here on the left, he is a very typical
presentation 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 function
like it's normally able to. And so it has a very
different presentation. Even though for both of them, insulin is not working properly and it results in hyperglycemia, which is the characteristic
finding in diabetes, depending on the underlying mechanism, whether or not you are
not producing insulin or whether the insulin just
isn't working properly, you still have hyperglycemia but the presentations
can be very different.
