Insulin triggers cells to absorb glucose from the bloodstream by inserting GLUT4 transporters into their membranes.

When blood glucose rises after a meal, the pancreas releases insulin. This hormone signals muscle and fat cells to insert GLUT4 transporter proteins into their surfaces. These transporters act like doorways, letting glucose flow from the blood into the cell where it can be used for energy or stored. Without insulin, glucose remains trapped in the bloodstream, unable to reach the tissues that need it.