Mechanisms of hormone action

A Example of steroid hormone action inside a target cell.
1. A steroid hormone molecule is moved from blood into interstitial fluid bathing a target cell.
2. Being lipid soluble, the hormone easily diffuses across the cell’s plasma membrane.
3. The hormone diffuses through the cytoplasm and nuclear envelope. It binds with its receptor in the nucleus.
4. The hormone– receptor complex triggers transcrip-tion of a specific gene.
5. The resulting mRNA moves into the cytoplasm and is transcribed into a protein.

B Example of peptide hormone action inside a target cell.

1. A peptide hormone molecule, glucagon, diffuses from blood into interstitial fluid bathing the plasma membrane
of a liver cell.
2. Glucagon binds with a receptor. Binding activates an enzyme that catalyzes the formation of cyclic AMP from ATP inside the cell.
3. Cyclic AMP activates another enzyme in the cell.
4. The enzyme activated by cyclic AMP activates another enzyme, which in turn activates another kind that catalyzes the breakdown of glycogen to its glucose monomers.
5. The enzyme activated by  cyclic AMP also inhibits glycogen synthesis