Stress as a bodily response (physiological model)

Click here to listen to BBC's Health Check which considers individual differences in the stress response.

Let’s get something straight right from the start.  The body’s reaction to stress is old fashioned.  In the modern World, in the vast majority of stress situations the body’s response to stress causes more harm than good.  However, in the olden days, before even Mrs Ashton, Mrs Wilson and I were born (though perhaps not Mr Dodd), like tens or hundreds of thousands of years ago, our present day response to stress would have been a lifesaver. 

Faced with danger such as a sabre tooth tiger or a warring tribe down the road then a sudden mobilisation of energy in the body was useful.  Consider the typical response to stress:

• Increased heart rate
• Increased blood pressure
• Relaxation of the lung’s bronchi (air channels widen)
• Release of glucose into the blood
• Dilation of pupils (letting more light into the eye)
• Slowing of digestion (allowing blood to flow to muscles, heart etc).

This is referred to as the 3fs response (fright: flight or fight) and serves a simple purpose.  It is pumping oxygen and glucose around the body providing energy to the areas where it’s most needed.  If the danger persists we can fight or we can turn and run.  If danger passes then very quickly the body can return to normal and primitive man can return to taking Dino for a walk!

BUT

Although our minds and behaviour have evolved since then (I speak for the majority of us here), our bodies and our biology have hardly evolved at all.  Today a typical stressor is likely to be examinations, bills, relationships, work etc.  However, our body does not distinguish between stressors, it reacts to them all in exactly the same way, i.e. the way it would have done thousands of years ago faced with life threatening stressors.  (This is why Selye called it the GENERAL adaptation response).  Exams therefore cause us to mobilise energy reserves, heart rate increase etc, as I’m sure you’ve noticed.  Unfortunately the response that was supposed to last seconds or minutes now lasts for the time of the exam stress, possibly weeks or months.  It now wears the body down and becomes a life threatener rather than a lifesaver.

The nervous system

I could bore you for hours here (as I’m sure some of you have noticed), but instead I’ll stick to the essentials. 

The Autonomic Nervous System (ANS).

This controls the functions that we have no conscious control over such as digestion, temperature and heart rate.  It can be split into two parts:

It’s obvious from this that the sympathetic nervous system is responsible for the stress response!  The Parasympathetic is left to return the body to normal when the threat has passed; it recharges the batteries for the next alert if you like.

The Hypothalamic-Pituitary–Adrenal Axis

Sounds complicated, lots of scientific words AND all joined up together.  It’s more straightforward than it seems.  I’ll assume that you’ve heard of the pituitary and adrenal glands, though the hypothalamus may be new to you. 

The important bits.

An area in the brain called the hypothalamus controls the body’s response to stress.  This is situated right next to the pituitary gland (sometimes referred to as the master gland because it controls the others) and both are located in the middle of the brain just behind the upper part of your nose!

In the stress response the Pituitary gland does two things. 

1. It sends nerve messages to the adrenal medulla (part of the adrenal gland)
2. It sends a chemical ACTH to the adrenal cortex (another part of the adrenal gland).

       Adrenal Medulla           Adrenal cortex

Note: a common measure of stress is skin conductance or Galvanic Skin Response (GSR).  This basically measure how moist your fingertips are.  The release of energy associated with stress causes sweating and increases the electrical conductivity of the skin.

That’s all there is to it.  The complicated bit done!!!

Research evidence

People without adrenal glands die when stressed unless they receive injections of cortisol (a steroid).  They have to be given training in avoiding or minimising stress!

Brady’s executive monkeys also supports the theory since the ‘executives’ died as a result of ulcers caused by long term disruption of digestion.  (See the key study later).

Remember that Brady’s study is flawed methodologically (in its methods) as well as being ethically very dubious.

Evaluation of the Physiological Model

This is clearly a very biological approach to stress.  It only considers events inside the body and sees stress as a purely physical response.  It does not consider differences between people, for example why one person’s stress is another person’s pleasure. 

Mason (1975) measured the levels of adrenaline produced by stressors in different people.  The same stressors produce different levels of adrenaline in different people depending on how they interpret the stress.  The physiological model does not consider people’s interpretations or perceptions of stress.

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