1. Different Types of Chemical Signals Can Be Received by Cells
Hormones: produced at great distances from their target tissues and carried in the circulatory system to various sites
Growth factors: released locally, acting on nearby tissue
Many messengers are Hydrophilic Compounds:
First messenger: Ligand
Second Messenger: such as cyclic AMP and calcium
Signal transduction: the ability of a cell to translate a Receptor-Ligand Interaction to change in its behavior or gene expression
Hydrophobic messengers
Act on nuclear receptors or cytosol, regulate the transcription of particular genes
Steroid hormones