Insulin signaling

[rturu]

Does insulin floating in the blood signal to the insulin sensitive tissues like muscle and body fat to prepare to absorb glucose
OR
is it the Islets of Langerhans that give out the signal directly somhow?

[kolean]

When glucose is in the blood (like after you eat a meal and you begin to digest the nutrients giving off glucose molecules that then transport thru the epithelial cells of the GI tract to the blood) it can then bind to a receptor on the islets of Langerhans located in the pancreas. This stimulates the islets to produce insulin that is then secreted into the blood and travels thru out the body. Insulin is a ligand for the insulin receptors that are found on the outside of many cells. Once the insulin binds to this receptor, it initiates a phosphorylating enzymatic cascade system in which the cell then can open the gated channels and let more than the normal passage of glucose into the cells. Storage enzymes are also participating in this particular cascade system, in which the excess glucose then goes into storage mode: glycogen and fat/adipose. This way the blood can be cleared of glucose in a timely manner, otherwise adverse effects begin to accumulate in the body.