Fortunately many glucose transport to tissue pathways don't
require insulin to facilitate the process. (ie: Insulin independent)
Examples are:
GLUT1 for RBC, BBB and Fetus.
GLUT2 for Renal, Liver ,Pancreas and small intestine.
GLUT3 for Neurons , Renal, Placenta.
GLUT4 in muscle and adipocytes(fat) cells however is insulin dependent
to Translocate GLUT4 receptors from intracellular vesticles (GSV)
to the plasma membrane (cell surface exocytic sites) to facilitate diffusion
of glucose from a high to low concentration gradient.(ATP not required).
Say in the case of insulin resistance (T2) inhibiting GLUT4 translocation,
the body can also stimulate GLU4 translocation via muscle activity(contraction)
for enhanced muscle glycogen storage with aim of achieving plasma glucose
homeostasis.
