Physiology of Stress

If there is a fire in the building, we can jump a flight of stairs that we would not be able to manage at another time. In simple terms, when the brain registers that a demand is being made and that an effort is needed, it triggers reactions in the body that include a release of various hormones. When any fearful condition occurs in front of us, our blood pressure soars, our pulse races, and we may even begin to sweat. These are part of a general pattern of reaction referred to as the flight – or – fight syndrome, a process controlled through the sympathetic nervous system. 

When an individual perceives that they are in a threatening situation or that they are unable to cope, then messages are carried along neurons from the cerebral cortex and the limbic system to the hypothalamus (areas of the brain). The anterior hypothalamus produces sympathetic arousal of the Autonomic Nervous System (ANS). The ANS controls the heart, lungs, stomach, blood vessels and glands. Due to its automatic action, we do not need to make any conscious effort to regulate our breathing or heart beat. The ANS consists of a sympathetic nervous system and a parasympathetic nervous system. Essentially, the parasympathetic nervous system conserves energy levels, and increases bodily secretions such as tears, gastric acids, mucus and saliva – which help to defend the body and aid digestion. The parasympathetic nervous system also aids relaxation. 

The sympathetic nervous system, however, prepares the body for action. In a stressful situation, it does the following:

1. Increases strength of skeletal muscles.
2. Releases clotting agents into blood to decrease bleeding from wounds.
3. Heart beats faster to pump blood more quickly to relevant body parts.
4. Increases sugar and fat levels.
5. Reduces intestinal movement.
6. Relaxes the bladder (bladder and bowels may empty).
7. Dilates the pupils.
8. Increases perspiration.
9. Senses become more alert to warn of danger.
10. Inhibits erection, vaginal lubrication by restricting blood flow.
11. Constricts most blood vessels but dilates those in heart, leg, arm muscles.
12. Increases rate of breathing to keep oxygen levels.
13. Dulls pain reactions to protect initially if there is physical harm.
14. The immune system is often affected.
15. The main sympathetic neurotransmitter is noradrenalin, which is released at the nerve endings.