Fourth heart sound (S4)

Not audible in normal adults

Heard in ventricular hypertrophy, where ventricular compliance is decreased

TLS Online TPP Program

#Id: 6542

#Unit 7. System Physiology – Animal

Fat and muscle cells express large amounts of the insulin-responsive glucose transporter GLUT4

TLS Online TPP Program

#Id: 6543

#Unit 7. System Physiology – Animal

In resting cells, virtually all of the GLUT4 is localized to small vesicles in the cytosol While some GLUT4 is in endosomes, most is in a unique small organelle termed the GLUT4 storage vesicle (GSV)

TLS Online TPP Program

#Id: 6544

#Unit 7. System Physiology – Animal

In GSV, much of the GLUT4 is tethered to the Golgi matrix, a network of coiled-coil proteins surrounding the Golgi complex,  by a TUG protein

TLS Online TPP Program

#Id: 6545

#Unit 7. System Physiology – Animal

Binding of insulin to the insulin receptor leads to activation of a protease that cleaves the TUG protein, releasing GLUT4-containing vesicles, which move along microtubules

TLS Online TPP Program

#Id: 6546

#Unit 7. System Physiology – Animal

Insulin also activates PKB which phosphorylates the Rab GAP protein AS160

TLS Online TPP Program

#Id: 6547

#Unit 7. System Physiology – Animal

Rab proteins in their active GTP-bound states, allow the GLUT4 storage vesicles to move along microtubules to the cell surface