Different Types of Chemical Signals
Can Be Received by Cells
• Chemical signals
– 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