Stress!

...as a bodily response

is

The subjective experience

of a lack of fit

between a person

and their environment.

Physiological

• Increased pupil size; allows more light in for better vision,

• Bronchial tubes in lungs dilate for great oxygen intake,

• Increase in heart rate; allows for greater blood flow to skeletal muscles,

• Sweat glands stimulated,

• Glycogen stored in the liver is converted to glucose for energy,

• Adrenal medulla is stimulated to release adrenaline.

Effect of Stress

Psychological

• Anxiety,

• Depression.

TYPES

OF

STRESS

Acute

• sudden stressors- such as a personal attack.

Chronic

• ongoing stressors- such as a stressful job.

Acute Stress

-the sympathomedullary pathway

Acute stressors arouse the autonomic nervous system (ANS).

This system is necessary because some bodily functions (e.g. your heartbeat) would not work as well if you had to think about them.

The ANS is divided into the sympathetic nervous system (SNS), this arouses an animal to be ready for a flight/fight situation, and the parasympathetic nervous system (PNS), which returns the animal back to a state of relaxation.

When an animal is exposed to an acute stressor, the SNS is activated, this prepares the animal for a flight/fight response. The sympathetic adrenal medullary system (SAM) has the key part of making a flight/fight response.

The SNS and SAM system together make up the sympathomedullary pathway.

The SNS

Neurons from the SNS travel to nearly every organ and gland within the body.

This prepares the body for a rapid action for when the animal is under threat.

Such responses include a rise in heart rate, blood pressure, increased pupil size and metabolic changes (like the mobilisation of fat and glycogen in the bloodstream).

Noradrenaline (aka norepinephrine) is the neurotransmitter released by the SNS to activate these internal body organs.

The

SAM

System

At the same time that the SNS is activated the SAM system alerts the animal through the release of adrenaline (aka epinephrine) into the bloodstream.

The adrenaline in the bloodstream is transported throughout the body to prepare the animal for flight/fight.

The SAM system is regulated by the SNS and also the adrenal medulla.

The

Adrenal

Medulla

Each adrenal gland has two distinct sections, the adrenal medulla-in the centre of the gland, and the adrenal cortex-around the outside.

Neurons of the SNS travel to the medulla, so that when it is activated it releases adrenaline into the bloodstream.

Once in the blood, the adrenaline has widespread effects on the body physiological systems.

These include:

• boosting the supply of oxygen and glucose to the brain and muscles.

• suppressing non-emergency processes-like digestion

Chronic Stress

-the pituitary-adrenal system

The pituitary-adrenal system is also known as the hypothalamic-pituitary-adrenal axis/HPA.

This has been seen as the body's 'stress system', controlling levels of cortisol and other important stress-related hormones.

Although both physical and emotional stressors activate the HPA, compared to the SAM system, activation of the HPA is much less easy to achieve.

This occurs in response to chronic stress situations.

The

Role

of

the

Hypoth

alamus

When stressors are perceived by the higher centres of the brain, an impulse passes to a small cone-shaped part of the brain- the hypothalamus.

The hypothalamus is the control system of the body's hormonal systems-these include those involved in the stress response.

Activation of a particular region of the hypothalamus, the paraventricular nucleus (PVN) leads to the production of corticotrophin releasing factor (CRF).

This is released in to the bloodstream in response to the stressor.

The

Pituitary

Gland

On the arrival at the anterior lobe of the pituitary gland, CRF causes the pituitary release and produce adrenocorticotrophic hormone (ACTH).

From the pituitary, ACTH is transported in the bloodstream to its target site in the adrenal glands, located at the top of the kidneys.

The

Adrenal

Cortex

Cortisol, released by the adrenal cortex, is responsible for several stress-related effects in the body.

Some of these are positive (e.g. a quick burst of energy and a lower sensitivity to pain)....

...whereas others are negative (e.g. impaired cognitive performance, higher blood pressure and lowered immune response).

Prolonged release of ACTH causes the adrenal cortex to increase in size in order to cope with increased cortisol production.

Long-term ACTH defiency causes it to shrink.

Feedback

The feedback process takes around 20 minutes to be completed, with cortisol levels typically rising quickly 20 minutes after the initial perception of an acute stressor.

This system is also very efficient at regulating itself.

Both the hypothalamus and pituitary gland have special receptors that monitor circulating cortisol levels.

If these rise above normal levels, they initiate a reduction in CRF and ACTH levels, with then brings cortisol levels back to normal.

Stress