The initial physiological response to stress is the same for all: increased heart rate and blood pressure, shortly followed by sweating and breathing faster.
These are a result of the hormonal surge that occurs to prepare us for action.
The psychological response varies, making stress so individual. What happens in our body when we perceive a situation as stressful? This requires knowledge of how the nervous system works.
Nervous system
There are two branches of the nervous system. The voluntary system controls conscious movement whereas the autonomic nervous system (ANS) controls involuntary and automatic bodily activity. It is the latter that is involved in the stress response.
The ANS comprises the parasympathetic system, which continuously maintains the resting state of all organs and processes, and the sympathetic system, which is excited mainly in difficult situations. It is the sympathetic system which prepares the body and mind for action through the secretion of hormones.
Stress hormones
The hormones involved in the stress response include adrenaline, noradrenaline, and cortisol. These are secreted by the adrenal glands. The inner region of the adrenal glands is part of the sympathetic nervous system and the bodys first line of defence and response to physical and emotional stress.
Noradrenaline and adrenaline
Adrenal glands release adrenaline and noradrenaline, at the same time as noradrenaline being released all over the body due to the action of the sympathetic nervous system. These chemical messengers activate two different types of receptors at various sites, preparing the body for action. For example, by activating beta receptors on the heart muscle, they help 'it' beat faster and stronger, so it can pump blood containing oxygen and nutrients to the muscles. Their action on the receptors in the walls of the coronary arteries allow the arteries to dilate, allowing more blood and oxygen through to the heart.
Adrenaline prompts an increase in the hormone glucagon, which is responsible for mobilising glucose normally stored in our muscle and liver as glycogen. This results in a sudden increase in energy for immediate action. Energy which is not utilised in sedentary situations, contributes to unhealthy fluctuations of blood sugar levels, which has consequences for cardiovascular disease, diabetes, anxiety and insomnia.
Cortisol
Cortisol is released from the adrenal glands following a sequence of events initiated by the production of cortiocotropin-releasing hormone (CRH) in the brain. Cortisol stimulates the production of extra nutrients such as glucose and fatty acids to help cope with the stress. Raised cortisol levels are associated with a suppressed immune system, heart disease, cancer, osteoporosis and ageing.
What else is happening?
Besides the dominance of the sympathetic nervous system and the release of hormones, other physiological processes occur in response to stress. The digestive system slows and the pituatary gland and brain secrete endorphins to reduce pain. These reactions are part of the survival function, concentrating energy on essential short-term processes such as heart beating rather than comparatively unnecessary digestion, and to prepare the body to cope with possible ensuing pain. The latter is why people in accidents and soldiers in battle can suffer injuries but report feeling little discomfort.
| Physical Reaction | Reasoning |
| Dry mouth | Parasympathetic nervous system inhibited - stops producing saliva |
| Pounding heart / fluttering or irregular beats | Sympathetic nervous system causes heart to beat faster and blood pressure rises to enable blood to reach parts of body that need it. |
| Sweating | Cools the body which in turn allows it to burn more energy |
| Tense muscles | Muscles contract when they are primed for action. In the absence of action, stiff neck and painful back can be experienced. |
| Tiredness | Depleted energy levels when stress is constant due to the parasympathetic nervous system diverting from the digestive process and storing energy, and the sympathetic nervous system taking over and effectively drawing on stored nutrients. |
| Loose stools / diarrhoea / IBS | Muscle contractions that move food along the gut either slow down, due to parasympathetic system diverting its actions from digestion, or starts working overtime to try and compensate. |
Although the physical reactions to stress have evolved for survival purposes, their repeated occurrence in inappropriate situations such as todays sedentary lifestyle, results in compromised health and ultimately disease.
03/06/2009