So far with this series, I've discussed the many difficulties involved in discussing and characterizing insulin resistance, IR. See Part I: A condition in dire need of diagnostic clarity and Part II: The Complexity of Hormone Resistance Phenomena. Insulin-mediated glucose transport, or "disposal" from circulation is the major action/phenomenon usually assessed or being discussed when a person (or lab animal) is described as "insulin resistant".
So in this part, I wanted to discuss glucose transport. This link is a nice tutorial about the action of insulin that includes an animation of ONE of its functions: glucose transport. Glucose cannot traverse membranes unassisted. In essence it must pass through protein "channels" from one side to the other. There are always glucose transporters, called GLUT's, present in the cell membrane, but they are not always at the exterior surface of the cell to receive glucose. Insulin binds to the receptor which signals movement of the transporters to the surface (translocation) allowing glucose to flow down the concentration gradient through the GLUT "channel". I've labeled the components in the screenshot below, and "taped" a short video of the animation from the tutorial so you don't have to go off-blog if you don't want to:
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