Physiology of Stress

March 21, 2006 at 9:09 PM

Introduction to the Physiology of Stress

The 'Fight or Flight' response, the hormones and the part of adrenaline in the stress response

What is the Fight of Flight response?

The major difference between organic and inorganic systems is the self-perseverance instinct. The world is an ever changing environment, demanding abilities of reacting, defending oneself, changing the inner or outer surrounding for one single aim: survival. Hence, when an animal is confronted with a perceived dangerous - it reacts. The animal will use as many resources as needed, as much energy as possible - to deal with the threat.

In the animal kingdom the rules of survival are simple - only the stronger survives. When faced with danger, the two main options are fighting (when you perceive the enemy to be weaker than you, or when defending your cubs or herd), and running away (when you encounter a huge hungry lion, for example). In face of danger, the body changes its inner-balance and priorities into a high physiological arousal, to enable these two functions (Hayes, 1994).

Outwardly, these interesting phrases have nothing to do with the business of psychotherapy and stress management. How on earth a homo-erectus fighting a mammoth is related to a modern businessman engaging in the stock market? Well, sadly enough - we are still, first and foremost, animals. The short period (something between 25,000-40,000 years) in which we exist is only an insignificant fragment in evolutionary terms - we are, in fact, 99% genetically identical with chimpanzees (Girbbin and Cherfas, 1982).

The fight or flight response (named by Cannon and Selye in the 1930s) is a pattern of physiological responses that prepare the organism (that's us) to emergency. When the external balance is disputed, our body changes its internal balance accordingly. The fact that modern problems do not require such means is exactly the setting of stress-related problems (Atkinson et al, 1996; Lev, 1987).

The manifestations of the F or F are mainly through two channels: the sympathetic branch of the ANS and the Endocrine system - both are closely interconnected (Atkinson et al, 1996; Carlson, 1994). The ANS effect many bodily functions instantly and directly, while hormones have slower yet wider effect on the body (Gross, 1998). Both hormones and neurones communicate with cells and create the delicate dynamic balance between the body and its surrounding, through paired systems and feedback mechanisms (Jacobs, 1973; Morgan, 1991

I will briefly describe some of the events occurring in our body, preparing it for either an F or F response:

Increased heart rate, blood pressure and respiration. Pumping more blood to the muscles, supplying more oxygen to the muscles and heart-lung system.

Increased sugar rates in the blood. Allowing rapid energy use, and accelerating metabolism for emergency actions.

Thickening of the blood - to increase oxygen supply (red cells), enabling better defence from infections (white cells) and to stop bleeding quickly (platelets).

Sharpening of senses. The pupils dilate; hearing is better etc., allowing rapid responses.

Prioritising - increased blood supply to peripheral muscles and heart, to motor and basic-functions regions in the brain; decreased blood supply to digestive system and irrelevant brain regions (such as speech areas), this also causes secretion of body waists, leaving the body lighter.

Secretion of Adrenaline and other stress hormones - to further increase the response, and to strengthen relevant systems.

Secretion of endorphins - natural painkillers, providing an instant defence against pain.

Atkinson et al, 1996; Hanson, 1986; Kandel, 1991

There are further systems involved in the F or F response, and even more consequences to it. It is clear that the F or F response is crucial to dealing with some short-term dangers but it is incapable of dealing with long-term stress. The grave consequences of long-term stress on our body and mind, is a direct result of this inadequacy.

What are hormones?

Derived from the Greek word for excitation horomao, a hormone is a chemical organic substance. It is produced by a system of ductless glands (the Endocrine system) in small doses, and secreted into the bloodstream thus being targeted to specific parts of the body. The hormones function as communication substances - they regulate and integrate various bodily functions. Hormones are directed to have a specific effect on the target areas. Unlike the nervous system, the glands are distant from the 'target area'; thus the hormones are indirect, slower and their influence is longer-lived than neural messages (Atkinson et al, 1996; Kandel, 1991; Lev, 1987; Thain and Hickman, 1995).


There is a good reason why the first discovered hormone (1894) was Adrenaline (Epinephrine in the US). Produced and secreted by the adrenal gland (that all its hormones are known as 'stress hormones'), adrenaline is secreted as a direct reaction to stressful situations, and its powerful effects are similar to those of the sympathetic branch of the ANS (such as increasing heartbeats, blood pressure, sugar-levels, muscle activity etc.).

Besides its hormonal functions, adrenaline is also an excitatory neurotransmitter in the CNS (indirectly controlling its own production). It is involved both in neural and hormonal processes and its effects as a neurotransmitter are further reinforced by its hormonal function (a positive feedback loop).

It is therefore by far the most important single hormone in regarding to stress - taking a major role in the stress reaction (and staying longer in the body than Autonomic Nervous System - [ANS] processes). (Atkinson et al, 1996; Kandel, 1991; Lev, 1987; Rossi and Cheek, 1988; Thain and Hickman, 1995)


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