Epinephrine (a.k.a.: Adrenaline ) is the most vital instinctual hormone for human kind to survive.
When in danger, fear or alert situations, the level of adrenaline increases in human body.
This leads to super quick increase in heartbeat and more accelerated bloodstream.More blood is sent to muscles, the amount of energy produced by metabolism reaches peak and pain receptors become blunt.
That helps body to run away from perceived threat or defend itself.(Which is commonly called "fight or flight response")
https://www.youtube.com/watch?v=GilWRuk81tk
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