Adrenaline binds with receptors on liver cell-surface membranes. This triggers a chain reaction inside the cells that eventually leads to the conversion of glycogen into glucose.

The second messenger model of hormone action involves a hormone (the first messenger) triggering the formation of a second messenger (cAMP) inside the cell, which activates enzymes to carry out a function.

It is the process where one hormone molecule can cause many cAMP molecules to be formed, and at each stage in the cascade that follows, the number of molecules involved increases.

1. Adrenaline binds to complementary receptor on the cell-surface membrane of a liver cell
2. The binding of adrenaline causes the protein to change shape, activating a G protein
3. This activates the enzyme adenylyl cyclase
4. The activated adenyl cyclase converts ATP into cAMP
5. cAMP acts as a second messenger, binding to and activating many protein kinases via phosphorylation, amplifying the signal from adrenaline
6. Protein kinases activate enzymes that catalyse the breakdown of glycogen into glucose

Glucose moves out of liver cells by facilitated diffusion and into the blood through channel proteins.

This increases the blood glucose concentration so that more glucose can be delivered to body cells for respiration.