Adrenalin, or epinephrine, is released by the body during stress. Adrenalin increases your heart rate, temperature, blood pressure, respiratory rate. It causes your bladder to relax but your urinary sphincter to contract; so even if you feel you want to pee, you can't. Adrenalin causes your salivary glands to decrease the release of secretions, so you feel you have dry mouth. It also causes decrease in intestinal motility, therefore resulting to constipation.