Whenever we face a challenge, whether a life-or-death situation or speaking in front of a crowd or even an exam, three chemicals initiate the fight or flight response of our body. Faster breathing, racing heart and loss of appetite are caused by actual chemical processes in the body.

One of the chemicals is cortisol. It is a hormone. It has a slow and long-lived response. It increases the blood glucose level. It suppresses the immune system because fighting an infection is not a priority when chased by a tiger. This is one of the reasons why long-term stress makes people vulnerable to diseases.

The other two chemicals are epinephrine and norepinephrine. These have an immediate and short-lived response. Both act as hormones and neurotransmitters.

As a neurotransmitter, norepinephrine heightens alertness. As a hormone, norepinephrine tightens blood vessels via vasoconstriction and raises blood pressure in the entire body. It suppresses digestion so that the energy required to digest food can be redirected to other muscles.

The main role of epinephrine is hormonal. It makes the heart pump more blood during every beat (increased cardiac contractility). It redirects blood flow towards skeletal muscles via dilating blood vessels in the arms and legs. It makes breathing more efficient via bronchodilation. It also increases heart rate, blood pressure and blood glucose level and suppresses digestion.

So, the response to challenges, threats and fear is not only psychological it is also biological.