THE BODY’S RESPONSE TO STRESS
The Pituitary Adrenal System
1) Hypothalamus is instructed by higher parts of brain to release cotricotrophin relasing factor (CRF)
2) CRF goes to Pituitary gland
3) Pituitary gland releases adrenocorticotrophic hormone (ACTH)
4) ACTH goes to Adrenal Cortex
5) Adrenal Cortex releases corticosteroids
The Sympathomedullary Pathway
Sympathetic: Hypothalamus activates sympathetic branch of the autonomic nervous system (ANS), stimulating the adrenal medulla and causing a release of adrenaline and noradrenaline in the bloodstream. We see a pattern known as sympathetic arousal:
· Heart rate and blood pressure increase
· Fats and carbohydrates mobilized
· Activity in digestive tract slows down
Parasympathetic: The opposite occurs as the body calms and relaxes.
1. Years and years ago these responses would protect us from predators or physical dangers
2. To successfully respond to these, we’d need the energy to fight or run away – the ‘fight or flight’ response – Cannon 1914
3. In modern society, stressors are more likely to be psychological and more long-term, so the physical stress response isn’t really needed and long term can be harmful
4. Positive stress that can be exhilarating is called eustress – e.g. jumping out of a plane with a parachute
General Adaptation Syndrome
noticed that rats could become ill even when given harmless injections, suggesting that the stress of the injection was causing illness. He proposed this 3 stage physiological response:
· The Alarm Stage – stressor is located, triggering the body’s stress response system to prepare for ‘fight or flight’
· The Resistance Stage – the stressor is coped with due to the body’s response, our bodies adapt after time. However, physiologically our arousal levels are higher than normal
· The Exhaustion Stage – the body can no longer cope with the long-term exposure to the stressor, alarm signs may return and depleted hormone levels cause stress-related illnesses (e.g. ulcers, anxiety, depression). Seyle called these ‘diseases of adaption’
These stages are supported by lots of scientific research, however the GAS theory only describes one response to stress, and neglects that the body’s reaction does vary (e.g. amount of adrenaline released can depend on how stressor is perceived).
Taylor et al. (2000) believe that the evolutionary tendency for females to resist ‘fight or flight’ to stay and protect offspring would lead to development of biological mechanisms to prevent ‘fight or flight’. They would shift attention to the young and befriend other females as a defensive network. This is called the ‘tend and befriend’ response.
Stress-related illness and the immune system
Stress responses that inhibit the immune system are called immunosuppression.
This is where stress directly causes an illness of the malfunction of the immune system. For example, coronary heart disease has been shown to the have a link with the S.A.M response. It is caused by increased heart rate and narrowed arteries (which are…