How does epinephrine produce the fight-or-flight response?

Epinephrine, a hormone secreted by the adrenal medulla, is a key mediator of the fight-or-flight response, which prepares the body to react to or retreat from acute threats.12

Mechanism of Action

Epinephrine initiates this response by binding to alpha-adrenergic and beta-adrenergic receptors on the surface of target tissues. When it binds to beta-adrenergic receptors, it triggers the activation of G-proteins, which stimulate the synthesis of cAMP (cyclic adenosine monophosphate). This molecule acts as a second messenger, rapidly propagating the signal within the cell to produce physiological changes.123

Physiological Effects

The specific response depends on the receptor type and tissue involved:2
* Cardiovascular: Activation of beta-receptors increases heart rate and the force of contraction, raising cardiac output and blood pressure.12
* Metabolic: Epinephrine stimulates glycogenolysis in the liver, breaking down glycogen into glucose to provide fuel for exertion. It also increases circulating free fatty acids.12
* Respiratory and Sensory: It dilates the bronchi to improve airflow and dilates the pupils to enhance visual acuity.12
* Vascular: While it constricts many blood vessels, it dilates those in skeletal muscles and the liver to prioritize blood flow during stress.2