Diabetes and hormones
Pancreatic functions
Olga Smirnova, Post-science
The pancreas participates in the regulation of digestion and regulation of lipid metabolism. The pancreas contains certain clusters of cells that perform an endocrine function. They are called Langerhans islands, sometimes – the pancreatic islet apparatus. They have several types of cells, each of which produces its own hormone. But the pancreas became famous because insulin is produced in the beta cells of the insular apparatus.
Insulin deficiency leads to type I diabetes mellitus. The fact is that such a prevalence of diabetes is due to the fact that insulin is the only hormone that can lower blood sugar, unlike all other hormones that affect processes, helping each other. For example, there are at least four hormones that increase blood sugar: adrenaline, glucocorticoids, glucagon, growth hormone. And if one of them does not work for some reason, then its function is replaced by others, and the blood sugar level rises. If insulin is not produced or does not work, then there will be no decrease in blood sugar, which will lead to diabetes mellitus.
Diabetes mellitus has been known for a very long time. Therefore, of all the hormones of the insular apparatus of the pancreas, insulin was discovered first, they are engaged in it a lot. Insulin is a hormone by which the history of biology or the history of molecular biology can be traced. Three Nobel Prizes were received simply for insulin and one more for its radioligand definition. The first Nobel Prize was for finally discovering this hormone, the second for discovering its primary structure (this, by the way, was the first protein whose primary structure was deciphered). The third one is for deciphering the spatial structure, and the fourth Nobel Prize is for the fact that a method for determining hormones in the blood was developed using the example of insulin, which is still used very successfully.
A close study of insulin played a cruel joke with other hormones of the pancreatic insular apparatus, because these hormones were not paid due attention for a very long time. It turned out that in addition to beta cells, which produce insulin, there are also alpha cells, which produce glucagon - it is an insulin antagonist, that is, it increases blood sugar. Because they are close to each other, they can inform each other about changes in their concentration without going into the blood: beta cell insulin acts on alpha cells, and alpha cell glucagon acts on beta cell insulin. In this way they maintain a constant level of sugar in the blood. If there is too much insulin, glucagon begins to be produced so that glucose does not fall too much. On the contrary, if there is too much glucagon, insulin begins to be produced. Such local negotiations between two hormones are very important for maintaining systemic balance.
It turned out that there is another type of cells in the insular apparatus – delta cells. They produce the hormone somatostatin. Somatostatin was known as a hormonal compound that is produced by the hypothalamus and reduces the production of growth hormone, the second name of which is somatotropic hormone. Therefore, this compound was called "somatostatin", that is, it reduces the production of somatotropic hormone. It turned out that the lowering effect of hormone production is characteristic not only for the somatostatin that is produced in the hypothalamus, but also for the somatostatin that is produced in the delta cells of the pancreas. It reduces the production of both insulin and glucagon. This is such a restraining start to implement a rapid response to changes in blood glucose levels.
More recently, epsilon cells have been discovered that produce the hormone ghrelin. Here you need to talk about the functions of insulin, which not only reduce blood sugar levels. Its production increases in response to food intake, that is, it is a satiety hormone. When eating, blood glucose increases, and insulin reduces this glucose level. That is, another effect of insulin is a decrease in food intake. It signals to the brain that the body is full. Ghrelin and its products grow during fasting. It just signals to the body that it's time to start eating. Such alternative effects of insulin and ghrelin help them to properly regulate the rhythm of food intake, one insures the other. The main amount of ghrelin is produced in the stomach. And this is understandable, because the reaction to hunger in the stomach is the first. But the additional products in the insular apparatus help both insulin and ghrelin to respond correctly to the diet.
I have already said that counterinsular hormones are important not only for blood sugar to grow, but also for blood glucose to be at a constant normal level. And glucagon copes with it very well. What happens if the hormone system of the insular apparatus stops working? I have already said that diabetes has been known since ancient times. But it was only in the 1970s that diabetes began to be divided into two forms: the first and the second type. It turned out that they have completely different reasons. Type one diabetes is associated with the fact that beta cells are destroyed - those cells that produce insulin. Accordingly, insulin ceases to be produced, and blood sugar increases, it appears in the urine, dehydration begins. And type 2 diabetes is associated with a decrease in insulin sensitivity: insulin receptors do not work well, proteins that conduct a signal from insulin to executive cells do not work well. As a result, type 2 diabetes occurs.
It turned out that the mechanisms of occurrence of these two diseases are completely different. Type I diabetes is an autoimmune disease. Autoimmune damage to beta cells causes a decrease in insulin production. Moreover, it is interesting that quite often this disease is provoked by infectious diseases. The fact is that viruses and virus components, for example, rubella, like beta cells, their structures are exposed on the membrane of beta cells, the body begins to perceive beta cells as foreign, and insulin stops being produced.
For type 2 diabetes, the picture is completely different. If in the first case there are internal defects of the immune system, it reacts incorrectly, then in the second case there are some defects of enzymes that are involved in carbohydrate and lipid metabolism. They are not so big, but an overload of lipid and carbohydrate metabolism can provoke the disease. That is, it is overeating, obesity, and so on. When there is too much load on enzymes that are somewhat weak in their reactions, type 2 diabetes begins to manifest. Accordingly, these two diseases are treated differently. If in the case of type I diabetes it is necessary to inject insulin, then in the case of type II diabetes it is necessary to support the body so that insulin sensitivity does not fall as much as it happens.
Now, with regard to type I diabetes, large developments have begun related to stem cells and an attempt to find another way of treatment: to stimulate the transition of stem cells into beta cells, to plant these beta cells in patients with type I diabetes, to make sure that they produce insulin. In animal models, this more or less becomes real, so I think we are on the verge of discoveries when type I diabetes will not only be compensated, but, one might say, almost cured.
Unfortunately, the proportions of type I and type II diabetes are different. There are much more patients with type 2 diabetes than with type 1 diabetes. Despite the various treatment options for this disease, no breakthrough is expected yet. It should be borne in mind that the hormones of the pancreas are also regulated by the hormones of the gastrointestinal tract. And it is the hormones of the gastrointestinal tract that inform insulin that the meal has begun, now the blood glucose level will rise and it is time for insulin to increase in order to cope with the increased glucose level. Therefore, the pancreas, as part of the digestive system, reacts to the hormones of the gastrointestinal tract.
About the author:
Olga Smirnova – Doctor of Biological Sciences, Professor of the Department of Human and Animal Physiology, Head of the Laboratory of Endocrinology of the Faculty of Biology of Lomonosov Moscow State University.
Portal "Eternal youth" http://vechnayamolodost.ru