Pathophysiology - Type II diabetes

- Diabetes Mellitus is a group of disorders that's caused by improper function of insulin, which is a hormone produced by the pancreas. And insulin is responsible for helping regulate blood sugar, or glucose levels, in the blood. Now since it's a group of diseases, there are actually multiple different underlying causes of diabetes mellitus. And one of these causes is known as Type 2 Diabetes. Now, before we dive into the actual cause of Type 2 Diabetes, let's first get a better understanding of how exactly insulin works. And there are two major steps. So, imagine that you just ate a big meal. Maybe like a bowl of pasta or something. And your body is currently absorbing all of those nutrients from your digestive system into your bloodstream. Now one of these nutrients is glucose, and as your body absorbs it, that glucose starts building up in the blood stream. And in this feeding or absorptive state, your body wants to store this glucose in places like the liver and muscle cells so that it can be used for energy later when the body needs it. But unfortunately, glucose on its own can't get into these cells. In a sense, these cells are locked. But fortunately, the pancreas is able to help with this problem. So there are a couple types of cells in the pancreas that sense blood sugar levels. And these cells are located in the islets of Langerhans. And these green cells here in the islets of Langerhans are meant to represent the Beta cells. And when the blood glucose increases, the Beta cells of the pancreas sense this change, and they secrete a hormone known as insulin into the blood. And what insulin does is it acts like a key that can unlock these cells so that the glucose can be stored in both the liver and the muscle cells. So you can see that there are two steps in order for insulin to function properly. And the first is that these Beta cells of the endocrine portion of the pancreas have to be functioning in order to secrete the insulin into the blood. And then second, these cells have to respond to the insulin in order to unlock them so that the glucose can be taken out of the blood to decrease the blood glucose levels. Now, diabetes mellitus can be caused by dysfunction at either of these two steps. So if the Beta cells aren't functioning properly or they're being destroyed, such as in Type 1 Diabetes, there isn't enough insulin to be produced to unlock the cells. And what happens is that the glucose builds up in the bloodstream, and that person will develop diabetes mellitus. However, similarly in step two, if the cells aren't properly responding to the insulin in the blood, then they can't be unlocked. And the glucose will build up in the blood vessels and you'll get hyperglycemia, and the person will develop diabetes mellitus. So this is what I meant earlier when I said that diabetes is a group of disorders, because multiple different mechanisms can result in diabetes mellitus. So, in general, Type 2 Diabetes is caused by dysfunction of this second step. And this is known as insulin resistance. So, in Type 2 Diabetes, the Beta cells of the pancreas are functioning properly, and they're able to produce insulin, but that insulin isn't able to have its proper effect on the cells throughout the body. However, it is important to note that as the disease does progress, the pancreas can become effective and eventually decrease its insulin production. But in general, Type 2 Diabetes is thought of as primarily due to this insulin resistance. So what exactly causes the cells to become resistant to insulin? Well, unfortunately there's no simple answer to this, and the cause of Type 2 Diabetes is very complex and includes many different factors that work together to cause the problem. So let's get a little bit better idea of this. I'm gonna just erase some of our work here, so we can get a little more room. So what are some of these risk factors? Well one of the most important ones is actually genetics. In fact, having a family history, say in someone's parents or grandparents, of Type 2 Diabetes is one of the biggest risk factors for developing Type 2 Diabetes. Other factors include obesity, hypertension, and increasing age. And it's the interaction of all these different factors plus more that end up resulting in insulin resistance. But how can we maybe understand this a little bit better? Well, one of the factors that we understand maybe a little bit better than some of the others is the effect of obesity. So let's bring back that lock I described earlier. So if you think of obesity as kind of this perpetual feeding state, or in a sense, that the body is continuously being exposed to insulin released by the pancreas in an effort to bring down the increased glucose from this perpetual feeding state. Over time, the receptors on the cells, or these locks, become desensitized to the insulin. And they become resistant to its effect. So let's use an analogy to help understand this idea of resistance. So instead of a lock, pretend this is a person. And this person decides to put on a baseball cap. So when you first put on a baseball cap, you can feel it on your head, however, over time, say 10, 15 minutes, this constant stimulation of the touch receptors results in a desensitization to the feeling of the ball cap on your head, and it feels like it's no longer there. So this is kind of similar to the cells in the body. If they're constantly exposed to this insulin, they'll stop responding to it, and the cell won't become unlocked. Now initially the pancreas is able to compensate for this resistance by producing more insulin. However, eventually as time progresses, the pancreas cannot keep up to overcome the insulin resistance, and eventually the body will lose its ability to lower the blood glucose level with insulin. And this will result in hyperglycemia and the complications that are associated with it. But this process can take time. In fact, from the time this insulin resistance starts to when someone would develop symptoms of Type 2 Diabetes can actually take multiple years. But at the same time, early diagnosis and treatment is critical to prevent the serious complications associated with diabetes. And for this reason, it's very important to screen people who are at risk, people who have some of these risk factors. It's important to screen them for Type 2 Diabetes, so they should regularly have their blood glucose levels monitored for hyperglycemia, so that it can be detected and treatment can be started even before he or she will develop symptoms. So I hope this gives you a better understanding of what causes Type 2 Diabetes. It's not caused by a problem with the pancreas itself and the ability to produce insulin. Instead, it's caused by this insulin resistance, by the cells throughout the body that are supposed to respond to insulin.