Representative Final Responses Glucose Transport Glucose entry into the primary insulin target tissues (skeletal muscle, heart, adipose tissue, and liver) occurs by facilitated diffusion, mediated by a family of transport proteins. Up to 12 members of this family have been identified, designated GLUT1-12. With regard to insulin action, the most important are GLUT1 and GLUT4.
Insulin is a highly pleiotropic hormone, with predominantly anabolic actions in a variety of tissues. Selectivity of final responses to insulin arises both from cell-specific expression of final effector proteins and by activation of different signaling pathways. We will consider first an overview of mechanisms of insulin action in normal human physiology, introducing the pathways,