Nutrition Science and Everyday Application - beta v 0.1

GLUCOSE REGULATION AND UTILIZATION IN THE BODY 199
Figure 4.16. Insulin binds to its receptors on the cell membrane, triggering GLUT-4 glucose
transporters to open on the membrane. This allows glucose to enter the cell, where it can be used
in several ways.
The figure also shows several different ways glucose can be used once it enters the cell.
• If the cell needs energy right away, it can metabolize glucose through cellular
respiration, producing ATP (step 5).
• If the cell doesn’t need energy right away, glucose can be converted to other forms
for storage. If it’s a liver or muscle cell, it can be converted to glycogen (step 4).
Alternatively, it can be converted to fat and stored in that form (step 6).
In addition to its role in glucose uptake into cells, insulin also stimulates glycogen and fat
synthesis as described above. It also stimulates protein synthesis. You can think of its role as
signaling to the body that there’s lots of energy around, and it’s time to use it and store it in
other forms.
On the other hand, when blood glucose falls, several things happen to restore
homeostasis.
1. You receive messages from your brain and nervous system that you should eat.
2. Glucagon is released from the pancreas into the bloodstream. In liver cells, it
stimulates the breakdown of glycogen, releasing glucose into the blood.
3. In addition, glucagon stimulates a process called gluconeogenesis, in which new
glucose is made from amino acids (building blocks of protein) in the liver and
kidneys, also contributing to raising blood glucose.