Glucose is necessary for all organs and tissues of the human body, being the main source of energy. Our organism gets glucose mainly from food; after its digestion glucose enters the bloodstream. However, most of the body’s cells are not able to independently obtain glucose from the blood, for this they need a special “key” that will “open” the cells and ensure the entry of glucose into them. The role of such a key is played by the hormone insulin.
The main source of insulin in the body is the pancreas, an organ behind the stomach that secretes a number of different substances. About 95 percent of the pancreas is the tissue that produces pancreatic enzymes that aid digestion, which are excreted through the internal ducts of the pancreas into the duodenum. The remaining 5 percent are hundreds of thousands of endocrine cells grouped into clusters known as the islets of Langerhans. These islets contain beta cells, which, when blood sugar levels rise, begin to produce the hormone insulin. Insulin molecules are gathered through the small blood vessels of the pancreas into the larger external vessels and then into the collar vein. From where, with the blood, insulin enters the liver and further into the circulatory system.
With the bloodstream, insulin is brought to those organs and tissues that need it for glucose uptake. These tissues include muscles, adipose tissue, liver and others. For example, glucose is the main fuel for the brain where nerve cells and chemical messengers use it for information processing. About 80% of glucose uptake happens in muscles where it stimulates cells’ growth and increases synthesis of fats and proteins.