Transportation of Glucose Across Cell Membranes: Rest vs. Physical Activity
Glucose Transport at Rest
Facilitated Diffusion
At rest, glucose primarily moves across cell membranes through facilitated diffusion, using special transport proteins called GLUT transporters.
NoteFacilitated diffusion is a passive process, meaning it doesn't require energy (ATP) to function.
The main steps involved are:
- Glucose molecules bind to GLUT proteins on the cell membrane
- The protein changes shape to move glucose through the membrane
- Glucose is released on the other side
GLUT Transporters
Different types of GLUT transporters exist:
- GLUT1: Found in most cells, especially red blood cells
- GLUT2: Present in liver and pancreatic cells
- GLUT4: The most important for muscle and fat cells
GLUT4 transporters are particularly important for athletes to understand as they're the primary means of glucose uptake in muscle tissue.
Glucose Transport During Physical Activity
Insulin-Independent Transport
During exercise, muscle cells can take up glucose without insulin through two main mechanisms:
- Contraction-Mediated Transport
- Muscle contractions trigger GLUT4 translocation
- More GLUT4 transporters move to the cell surface
