Stress- Part 1

The fight-or-flight response is the body's immediate reaction to a threatening situation. This could happen if you are in a fight, feel threatened, or even if you have to give a speech.  Walter Cannon (1927) came up with a theory of the 'fight-or-flight' response. The key idea is that an animal or person reacts to an immediate threat by releasing energy and preparing for action- either self-defence or running away. No matter which option is taken, the body will benefit from energy and oxygen to the muscles, improved vision, reduced tendency to bleed, etc. Because this is the response to an immediate threat, certain longer-term processes can be switched off, for example digestion, as immediate survival is much more important.

The environment of evolutionary adaptiveness (EEA) means the environment in which human ancestors are thought to have lived for most of the evolution of our species. It is thought that humans evolved in the African savannah, and lived in small tribes of hunter-gatherers for approximately two million years. It is only in the last 10.000 years that we have developed agriculture and lived in settled villages and towns. This helps to explain why the stress response can be unhelpful in the modern world.

This response evolved in our evolutionary past to aid survival. It helps to explain why our heart rate rises and we release energy in response to threats. The response is an over-generalisation. Animals such as cats respond differently in a fight, and some animals such as snakes use a 'play dead' strategy in response to a threat. The response only covers immediate threats, and doesn't explain prolonged stress.

Two stress responses:

The sympathetic adrenal- medullary (SAM) system

This process involves the autonomic nervous system, the branch of the PNS which controls the automatic processes of our organs. This has two branches- sympathetic branch, which takes control when the body is stressed or active, and the parasympathetic branch, which takes control when the body is at rest. When the body is stressed, nerves from the sympathetic branch of the ANS stimulate the centre of the adrenal glands to release adrenalin- the hormone which is most closely associated with symptoms of the fight-or-flight response, such as raised heart rate.

The HPA axis

The second process which causes the fight-or-flight response is the action of the endocrine system, the body's network of glands which release hormones. This system is regulated by an area of the midbrain called the hypothalamus. In stress, the hypothalamus instructs the pituitary gland to release a hormone called ATCH, which in turn instructs the adrenal cortex to release stress hormones such as cortisol. These hormones help to release the energy needed to fight stress, and trigger the changes in the body which cause the fight-or-flight response. This set of processes is called the hypothalamic-pituitary-adrenal (HPA) axis.

The way a person reacts to the stress hormone cortisol may also depend on sex. Taylor et al. (2000) found that the hormone oxytocin can reduce cortisol. Oxytocin is affected by sex hormones: it is boosted by oestrogen, whereas testosterone makes it less effective.