First messenger

Definition

A first messenger is a hormone or neurotransmitter that binds to a receptor on the cell surface, initiating a signaling pathway inside the cell. It does not enter the cell but triggers a cascade of reactions by activating second messengers.

Related terms

Hormone: A chemical substance produced in the body that controls and regulates the activity of certain cells or organs.

Receptor:

A protein molecule on the cell surface or within cells that binds to specific molecules like hormones, allowing them to exert their effects.

Second Messenger: Intracellular signaling molecules released by the cell in response to exposure to first messengers, amplifying the signal within the target cell