The Physiology of Stress

Hello.

My name is Lydia Tomba and I'm a research fellow

at the department of psychology at the University of Cambridge.

This lecture will be about stress.

In the first module,

we will talk about the physiology of stress and its relation to health.

So the concept of stress describes a state of an

organism when homeostasis is threatened or perceived as threatened.

So what does homeostasis mean? Homeostasis is a state of balance.

So when our body function, in its normal way, how it's supposed to function

when we are exposed to a stressor, our body needs to take

extra measures to deal with that stressor and

then returned back to its normal functioning.

This kind of stress response has also

been described as the general adaptation syndrome.

This general adaptation syndrome was first described by Hans Celia,

and it kind of tries to broadly describe the pattern

of responses our body goes through when facing a stressor.

And these responses are summarised into three stages alarm,

resistance and exhaustion.

So the first stage alarm occurs when we first perceive something as stressful,

and then our body initiates a stress response.

Um, I will talk about the physiological steps of a stress response in more detail.

In a bit,

the second stage is called resistance.

So if the perceived stress continues,

our body stays activated at a higher metabolic level

in an effort to offset the persistent stress.

The body, however, cannot maintain this level indefinitely,

and eventually the resources will deplete.

And that leads to the third stage, which is exhaustion.

So prolonged exposure to a stressor

results in the depletion of the body's resources.

Um, which caused the bodily functions to deteriorate and eventually, um,

can lead to a variety of health issues,

which I will talk about at the end of this module.

So what is a stress response?

On a physiological level,

Stress is known to trigger two different adaptive systems within our

body that both originate from a brain region called the hypothalamus.

The first system is a really fast reacting system,

and it starts pretty much immediately after we perceive a stressor.

It's called the sympathetic adrenal medullary System, or S A M system.

The second system is much slower.

It actually peaks around 20 to 40 minutes after the onset of the stressor,

and it is called the hypothalamus pituitary adrenal axis.

or h p A axis.

So the stress reactions in the S A M system stimulate

the release of adrenaline and nor adrenaline from the adrenal medulla,

which leads to the activation of the sympathetic nervous system.

These reactions, for example, are increased in heart rate increased in sweating,

um, and blood pressure.

Adrenaline also leads to an increased glucose level in our blood,

and that provides our body with increased energy

to face the challenges that it is facing.

Um, activation of the second bodily system.

The H P A axis, as I said, peaks a bit later in this whole stress response,

and it leads to a release of glucocorticoids from the adrenal cortex.

This is achieved by secretion of the cortical drop in

releasing hormone from the para ventricular nucleus of the hypothalamus.

This in turn results in a release of the, um of glucocorticoids

and the primary glucocorticoids in humans is cortisol.

This, when released into the bloodstream amongst other things,

also elevates blood glucose levels, uh, in various parts of the bodies.

Um,

another very important function of cortisol is that

it actually serves as a negative feedback loop.

So

in addition to being part of the stress response.

It also is a negative feedback,

meaning a signal to stop the stress response once it is released.

And overall, all these changes, um,

of the stress response serve to provide more energy, um,

for our body to deal with a certain challenge.

So, for example, that would mean either run, for example, from a threat or fight it.

And this is why the stress response has

also been labelled the fight or flight response.

So what happens in the body when there is a repeated exposure to stressors,

also called chronic stress?

Um, so, as I said, this stress response has a certain function.

It is here to protect our body from certain challenges and to help us face them.

However,

the kind of excess energy that we received during a stress response

means that the excess energy needs to be taken from somewhere,

right.

So this means that systems within our body that are

not necessarily relevant for helping us deal with challenges,

for example, digestion

and certain parts of our immune function.

They are kind of running on low mode during a

stress response because they are not essential during this.

So this obviously means that if we

are exceedingly or repeatedly exposed to stressors

in certain bodily functions have to run on low mode all the time.

That means that our bodies are more prone to develop health problems.

One very established finding is that chronic stress suppresses immune function

in particular, um, glucocorticoids stress hormones.

So cortisol are regarded widely as being immuno suppressive.

Um,

and they're actually also used in clinic in clinics as anti inflammatory agents.

So, for example, when you would have an auto immune disease,

so that means your immune system would respond

to strongly to certain things within our environment.

Uh, you might be given cortisone, which is a synthetic form of cortisol by a doctor,

which will suppress your immune system.

Another very consistent finding.

Um, there is that high levels of cortisol from long term stress will increase blood,

cholesterol, blood sugar and blood pressure.

And these are common risk factors for heart disease.

Another, um,

important kind of factor of stress is that it can

help promote build up of plaque deposits in your arteries,

again

promoting the development of certain heart diseases.

And in addition, when people have a lot of stress they tend to engage in behaviours,

um,

that are kind of sort of helping them to deal

with the stressor but are not necessarily healthy For example,

smoking or overeating.

Or they choose.

They might choose to do other unhealthy behaviours, um, to deal with stressors.

And that, in turn, can further impair your health.

So this is the end of the first module.

And to sum up, we talked about the physiological stress response.

The main sort of players in the stress response are adrenaline and cortisol,

both coming from two different bodily systems.

One is called the ECM System, which is fast reacting, and the other the H P A axis,

which is slower and also serves as a negative feedback.

We have heard that acute stress, so the immediate stress response is something

that is actually quite healthy, and it helps us deal with stressors.

However, if we experience the stress response chronically,

it actually makes us or it promotes disease and

certain problems such as immuno suppression or heart disease.