Insulin synthesis is induced in the organism when food is ingested. Insulin is a hormone that induces glucose uptake by cells across the cell membrane. A decrease in insulin synthesis leads to an increase in blood glucose levels in the blood.
What is insulin synthesis?
Insulin is the only hormone in the body that can lower blood glucose levels in the blood. Insulin synthesis is always necessary when carbohydrates are supplied during food intake. Insulin is the only hormone in the organism that can lower the blood glucose level in the blood. Insulin synthesis is always necessary when carbohydrates are supplied during food intake. Insulin synthesis takes place in the Langerhans cells of the pancreas. If too little insulin is produced, the blood glucose level rises because the glucose is no longer transported into the cells. Excessive insulin synthesis leads to low blood sugar (hypoglycemia) with cravings, restlessness and the threat of nerve damage. Insulin synthesis occurs intermittently and is always stimulated by food intake. If the carbohydrate intake is reduced, for example by starvation, the blood glucose level drops. Glucagon, the antagonist of insulin, is formed to a greater extent. Glucagon increases blood glucose levels through gluconeogenesis. As a result, the secretion of insulin decreases and its synthesis is restricted. Overall, insulin synthesis is part of a complicated regulatory mechanism to keep blood glucose levels constant.
Function and role
The provision of insulin ensures the supply of energy and anabolic substances to the body. Insulin has an anabolic influence on metabolism. In this context, insulin provision includes both insulin synthesis and insulin secretion. Insulin is produced and stored in the islet cells of Langerhans in the pancreas. When blood glucose levels rise, glucose enters the interior of the beta cells of the islets of Langerhans via vesicles, which immediately release stored insulin. At the same time, insulin synthesis is stimulated. Initially, an inactive preproinsulin molecule with 110 amino acids is formed on the ribosomes. This preproinsulin consists of a signal sequence with 24 amino acids, the B chain with 30 amino acids, an additional two amino acids and a C chain with 31 amino acids, another two amino acids and an A chain with 21 amino acids. After its formation, the stretched molecule is folded by the formation of three disulfide bridges. Two disulfide bridges connect each of the A and B chains. The third disulfide group exists within the A chain. The preproinsulin is initially located in the endoplasmic reticulum. From there, it is transported across the membrane to enter the Golgi apparatus. During ER membrane passage, the signal peptide is cleaved, which then remains in the cisternae of the endoplasmic reticulum. After cleavage of the signal sequence, proinsulin is formed, which has 84 amino acids. After uptake into the Golgi apparatus, it is stored there. When there is a stimulus for release, the C-chain is cleaved off by the action of specific peptidases. Insulin is now formed, which consists of an A chain and a B chain. The two chains are connected only by two disulfide bridges. A third disulfide group is located within the A chain to stabilize the molecule. Insulin is then stored in the vesicles of the Golgi apparatus in the form of zinc-insulin complexes. Hexamers are formed, which stabilize the structure of insulin. The release of insulin is triggered by certain stimuli. The increase in blood glucose level is the most important triggering stimulus. However, the presence of various amino acids, fatty acids and hormones also have a stimulating effect on insulin secretion. The triggering hormones include secretin, gastrin, GLP-1 and GIP. These hormones are always formed when food is ingested. After food intake, insulin secretion occurs in two phases. In the first phase, stored insulin is released, while in the second phase its new synthesis takes place. The second phase is not completed until the cessation of hyperglycemia.
Diseases and medical conditions
When insulin synthesis is impaired, there is an increase in blood glucose levels. Chronic deficiency of insulin is referred to as diabetes mellitus.There are two types of diabetes, type I diabetes and type II diabetes. Type I diabetes involves an absolute lack of insulin. Due to the absence or due to a disease of the islet cells of Langerhans, too little or no insulin is produced. Causes include severe inflammation of the pancreas or autoimmune diseases. The blood glucose level is extremely high in this form of diabetes. Without insulin substitution, the disease leads to death. Type II diabetes is caused by a relative lack of insulin. In this case, sufficient insulin is produced, and insulin secretion is even increased. However, insulin resistance is increased because the effectiveness of insulin is reduced due to a lack of receptors. The pancreas must produce even more insulin to achieve the same effects. In the long term, this increased insulin synthesis leads to the depletion of the islets of Langerhans. Type II diabetes develops. Increased blood glucose levels can also occur as part of hormonal regulatory disorders. Thus, increased cortisol activity results in increased glucose from amino acids through gluconeogenesis. As a result, insulin synthesis is permanently stimulated in order to lower the blood glucose level again. The excess glucose is thereby transported into the fat cells, where increased fat formation takes place. Truncal obesity develops. The condition is known as Cushings Syndrome. Permanently high insulin synthesis can also be triggered by a tumor in the islet cells of Langerhans. This is hyperinsulinism, which is often triggered by an insulinoma and leads to repeated hypoglycemia.
