A term introduced by the US physiologist Walter Bradford Cannon
(1871-1945), and popularised in his book 'Bodily changes in pain,
hunger, fear and rage' (1929), for the syndrome of physiological
responses of an organism confronted with a situation that evoles fear,
pain, or anger, such responses being mobilized by the secretion of
adrenalin (epinephrine) from the adrenal medulla, preparing the organism to fight or to flee.
It includes increased blood pressure, accelerated heart rate, deepened
respiration, increased sweating, dilation of the pupils, diversion of
blood flow from the digestive tract to the skeletal muscles and
cessation of digestive processes, release of sugar from reserves in the
liver, and closure of the sphincter of the bladder, leading to retention
of urine.
Source: The Oxford Dictionary of Psychology - Andrew M. Colman (4th edition, 2015: Oxford University Press).