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Insulin from beta cells will reduce blood glucose levels
After eating a meal that contains carbohydrates, such as sugary or starchy foods, blood glucose levels will begin to rise. These increased levels of blood sugar are detected by beta cells in the pancreatic islets. The same beta cells respond by secreting insulin. Insulin is released directly into the blood, where it facilitates the conversion of soluble glucose into insoluble glycogen that can then be stored in the liver and muscles. When glucose becomes glycogen, it is no longer in the blood,
capillary network on the islet
islet contains beta cells
But they are stored in the muscles and the liver in insoluble form. Therefore, blood sugar levels will fall to a normal homeostatic level.
In addition to this mechanism, insulin also facilitates the transfer of glucose through cell membranes, from tissue fluids and blood, to body cells. In the absence of insulin, most cell membranes are impermeable to the passage of glucose. This is because glucose is a water soluble molecule while cell membranes are based on lipids. When an insulin molecule reaches a cell membrane, it is combined with a specific insulin receptor protein in cell membranes. The combination of insulin and the insulin receptor triggers changes within the cell that result in the opening of glucose channels or "gates" through which glucose can pass. This means that more glucose, under the influence of insulin, passes from the tissue fluids of the body to the cells. Once in cells, glucose can be metabolized in the mitochondria to produce energy. Clearly, if the glucose is in the cells, it is no longer in the blood, so the levels in the blood are reduced again. The combination of the mechanism of glucose to glycogen and the transport of glucose to cells means that insulin causes the blood glucose level to fall to a normal homeostatic level. Insulin is actually a small protein composed of 51 amino acid units. This is the reason why the therapeutically used insulin should be injected if required; if ingested, the enzymes that digest the proteins in the stomach will simply digest it and make it ineffective.
Video credits to Dr. John Campbell YouTube channel