QUESTIONS & ANSWERS: GLOSSARY
Stress
Medically speaking, this means situations like fight and flight; similar reactions occur with mental stress. Experimentally stress can be induced by asking someone to perform some difficult mental arithmetic. The responses occur from activation of the "defence centres" in the brain and include rises in heart rate and blood pressure, mediated by the sympathetic nerves and adrenaline.
Many people have thought that a lot of stress in the lifestyle predisposes people to coronary heart disease. Although this has not been proved, an explanation for it would be that adrenaline, and noradrenaline (released from sympathetic nerves), activates thrombosis via the platelets (see atherosclerosis).
An acutely stressful situation, with adrenaline release, can increase the stress because a sensation of fear (releasing more adrenaline) is one of the effects of adrenaline. This is an example of a "snowball effect" or positive feedback. Adrenaline also stimulates breathing; overbreathing is a feature of "panic attacks". These acutely stressful episodes can trigger coronary thrombosis and a heart attack through activation of platelets. Overbreathing causes the coronary arteries to narrow because the inside of the smooth muscle cells in the arterial wall become alkaline. The high blood pressure can make the damage to the heart worse.