The Physiology of Stress

Question 1

What is stress?

Answer 1

An emotional response to situations of threat. Such threats may be physical such as a spider about to attack you, and some threats may be psychological, for example worrying about exams.

Question 2

How does your body respond to stress?

Answer 2

Your body produces a short-term (immediate) response and, should the stressor continue, a long term (ongoing) response.

Question 3

What is the short term response to stress?

Answer 3

The Sympathomedullary Pathway

Question 4

How does the Sympathomedullary pathway respond to stress?

Answer 4

A signal is sent down the sympathetic branch (SNS) of the Autonomic Nervous System (ANS) which then stimulates the Adrenal Medulla.

The signal is sent via the Central Nervous System to the two endocrine glands located just above the kidneys. The middle part of the adrenal gland (Adrenal Medulla) responds by releasing Adrenaline and smaller amounts of Noradrenaline into our bloodstreams.

Adrenaline and noradrenaline circulates through our bodies and affect the key target organs such as the heart and muscles.

After a few minutes the Parasympathetic branch of the ANS will start. This will reduce the “fight or flight” response and bring the body back to normal.

Question 5

What is the long term response to stress?

Answer 5

The Hypothalamic Pituitary-Adrenal System

Question 6

How does the Hypothalamic Pituitary-Adrenal System respond to stress?

Answer 6

The Hypothalamus is stimulated when the brain notices a stressor.

A signal is sent to the pituitary gland in the brain which releases a hormone called ACTH.

ACTH travels through the bloodstream down to the Adrenal Cortex (the outside of the adrenal gland) which stimulates it to release cortisol into the bloodstream.

The cortisol releases glucose from the liver to be used by the muscles as energy and suppresses the immune system to redirect energies to other areas of the body, for example brain and muscles. This process is called immunosuppression.

Question 7

What is the General Adaptation Syndrome (GAS)?

Answer 7

When animals are exposed to unpleasant stimuli, they display the universal response to all stressors.

Question 8

What did Seyle research and what did he do?

Answer 8

GAS - observed that in lab animals and human patients the fight or flight response was only the first of a series of reactions

He reported that the rats that he was experimenting on showed physiological changes that were directly linked to the injections that they received during the experiments, but that what was actually being injectors was less important than the fact they were getting an injection.

The rats were then exposed to various types of harmful stimuli, including extreme cold, surgical injury, excessive exercise, severing the spinal cord and nearly lethal doses of drugs.

The rats developed the same physiological symptoms each time, including (over time) the development of stomach ulcers

Question 9

What did Seyle conclude from his research?

Answer 9

Stress is “the non-specific response of the body to any demand”

Question 10

What are the three stages of GAS?

Answer 10

Alarm reaction
Resistance
Exhaustion

Question 11

What is the alarm reaction stage of GAS?

Answer 11

When we come across a stressor the fight/flight reaction is triggered. This is part of the sympathetic branch of the autonomic nervous system(ANS). This stage deals with acute stressors. It is at this stage that the sympathetic adrenal-medullary system (SAM) becomes activated. This is controlled by electric impulses through nerves, making the response fast.

Question 12

What is the resistance stage of the GAS?

Answer 12

If the stressor is not dealt with then the endocrine system helps us to maintain our response, through the Hypothalamic pituitary adrenocortical axis (HPA). This is a hormonal response and travels through the blood, making this a slower response.

The hypothalamus sends a message to the pituitary gland which releases ACTH. This is what causes the adrenal Cortex to release cortisol. This stimulates the liver to release glucose and also suppresses the immune system

Question 13

What is the exhaustion stage of the GAS?

Answer 13

This stage occurs when the body can no longer keep up with the stressor, and the body’s resources have become depleted. It is caused by severe long term or repeated stress, and it is in this stage that illness is most likely.

Once ACTH and cortisol are in the blood stream, the production of more is inhibited. The adrenal glands no longer function properly and they actually increase in size. Blood glucose levels tend to drop, which can result in death. Psychophysiological disorders may develop, e.g hypertension, asthma and peptic ulcers.

Question 14

Behaviours/Emotions in the Alarm Reaction stage?

Answer 14

Heartbeats faster

Pupils dilate

Question 15

Behaviours/emotions in the exhaustion stage?

Answer 15

Exhausted
Lack of sex drive
Lack of interest

Question 16

Finish the evaluation : biological research generally relies on male animals because females hormones fluctuate with ovulation and this complicates matters.

Answer 16

Conclusions drawn from earlier research may reflect a male bias. Taylor et al suggests that female behavioural responses to stress are a tend and befriend method, rather than fight or flight response.
Evolutionary research states that women had a more nurturing approach forming allies as a method of protecting her offspring. Studies using rats have suggested that there may be a physiological response in females that inhibits fight/flight - the release of oxytocin, as this hormone increases relaxation, reduces fearfulness and decreases the stress characteristics of the fight or flight response. This means that the standard description of the SAM and HPA systems are gender bias.

Question 17

Finish the evaluation: negative consequences of the fight or flight response

Answer 17

The fight or flight response does not determine your survival in this day and age. The fight or flight response was used for hunter/gatherers who would be fighting for their food. However, in modern civilisations food is in supermarkets for us, so we do not have to suffer in these situations anymore. Thus, the fight or flight response is an outdated response to stressors.

Question 18

Finish the evaluation: Stress related illness may not be due to depletion of resources as the GAS model suggests.

Answer 18

The GAS model proposes that resources become depleted so that the body can no longer fight infections. However, more recent research has shown that many resources such as sugars, neurotransmitters, hormones do not become depleted even under extreme stress. The current view is that the exhaustion phase associated with increased hormone activity such as cortisol, and it is this rather than depletion of the resources that leads to stress related illness. Thus, the GAS model is an inaccurate representation of the universal response to all stressors.

Question 19

Finish the evaluation : individual differences of the GAS

Answer 19

Seyle himself acknowledged that stress impacts each individual differently. What one person considers to be extremely stressful, another person experience as only mildly distressing. Therefore, the GAS cannot be considered a “universal” response to stress as it doesn’t consider individual differences.

Question 20

Finish the evaluation: The GAS could be manipulated by training - on experiencing stress on a regular basis our bodies adapt to cope with it.

Answer 20

This ability to manipulate our stress response is particularly useful for endurance sports and affects how athletes train for strenuous competitions. For example, a long distance runner may undergo endurance training to adapt to and cope with long periods of physical exertion (Kraemer and Ratamess)