You also realize probably, when we get so much anger or high levels of stress, after some point we have terrible stomach ache, like really heavy pain. Why is that? How stress or anger can effect our stomach? What is the mechanism?
Cortisol produced from the zona fasciculata of the adrenal cortex is directly caused by stress.
According to http://en.wikipedia.org/wiki/Cortisol
Cortisol stimulates gastric-acid secretion. Cortisol's only direct effect on the hydrogen ion excretion of the kidneys is to stimulate the excretion of ammonium ions by deactivating the renal glutaminase enzyme. Net chloride secretion in the intestines is inversely decreased by cortisol in vitro.
This increase in gastric-acid secretion can irritate the lining of the GI tract, especially if there are ulcers or inflammation, resulting in pain. In addition, the fight-or-flight response causes
inhibition of stomach and upper-intestinal action to the point where digestion slows down or stops.
Those things, paired with increased muscle tension and vasoconstriction cause pressure changes in the GI tract, which can cause pain.