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When scientists study the physiology of stress responses over time, they usually break down the stress responses into three phases, each involving different chemical messages working through different pathways. These three phases are the Acute Stage, the Intermediate Stage, and the Chronic Stage. We will look at the chemistry of each, and then discuss the implications of that chemistry on the well-being of the body.

The Acute Stage works with a chemistry that is very rapid to bring into operation, very strong in its responses, but very short-term in nature. Below you will find is a summary of the Acute Stage.

ACUTE (short-term)

Mediated primarily by neural pathways

Chemistry through the direct sympathetic nervous system

Acetylcholine and norepinephrine released

Because the communication pathways for the acute stress response are neural (through the brain neurons), the communication is very rapid, and very strong

But the neurotransmitters involved disintegrate and get re-absorbed very rapidly, and the stores of the chemicals used in communication can become exhausted under intense and constant stimulation. This stage of the stress response is designed to get you very geared up, to be able to respond very powerfully and very quickly, but not for very long.

If the stress response has to continue, the body will need to move into the intermediate phase, in which different chemical mechanisms become involved. This stage is summarized on the next page.


Intermediate (medium-term)

Mediated by neural endocrine pathways

Adrenal medullary stimulation begins

Adrenalin and noradrenalin released into systemic circulation

The second phase of stress response begins when a specific part of the brain - called the adrenal medulla - receives messages that a stress response is needed that will involve the whole body. The adrenal medulla sends out messages that result in the release of two important stress chemical throughout the body. These two chemicals are adrenalin and noradrenalin. When these two chemicals go into systemic circulation throughout a person's body, they cause the body changes that are associated with the "fight or flight" responses.

These responses, which provide the body with more energy, more focus, and a heightened sense of arousal, are designed to start about 20 to 30 seconds after the acute responses. This timing is not accidental. The intermediate phase is beginning right about the time that the acute phase is beginning to run out of energy. In this way, the body has a second response system, in case the event is not handled by the acute response.

Because of the chemistry involved, this second response phase can last much longer than the acute phase. Ideally, the intermediate phase of the stress response gives the person several minutes to utilize the increased energy, and handle the event in question. From the body's perspective, this means to fight, run, or seize the opportunity.

If the event is not handled in this time frame, then the body calls upon the last phase of the response, the chronic phase. The chronic phase is the most complicated part of the stress response. It involves the most chemical messages and chemical pathways, and affects the most parts of the body.

A summary of this response phase is presented below.

CHRONIC (long-term)

Mediated by endocrine pathways

Adrenal cortical responses

-Corticotropin Releasing Factor (CRF)
-Adrenocorticotropic Hormone (ACTH)
-Glucocorticoids (cortisol and corticosterone)
-Mineralocorticoids (aldosterone and deoxycorticosterone)

Somatotropic responses

-Growth Hormone

Thyroid responses

-Thyrotropin Releasing Factor (TRF)
-Thyroid Stimulating Hormone (TSH)

As you can see, there is not a single system of response at this phase. There are several. Each of these brings to bear different resources to help the body gear up for the challenge over time. The adrenal cortical responses pick up where the systemic release of adrenalin and noradrenalin leaves off. The sustained neural arousal in the stress response eventually leads to the secretion of corticotropin releasing factor (CRF) from a deep region of the brain. The CRF travels to the front part of the pituitary gland.

The pituitary responds by releasing adrenocorticotropic hormone (ACTH) into the blood stream. ACTH then causes the adrenal cortex to release two important groups of steroidal chemicals. The first group is made up of glucocorticoids. As its name implies, this is a group of chemicals that, among other things, has effects on the energy supply from glucose in the blood. The second group is made up of mineralocorticoids. These chemical affect the actions of minerals, such as calcium and sodium, in the bloodstream.

The result of the work of these chemicals is a longer term increase in available sources of energy, and changes in the body to be able to use these increased sources of energy, so that the body can handle increased demands over time. As a short-term strategy to meet a challenge, this is very effective. It allows the body to work at a much higher level.

Unfortunately, the body pays a price for this strategy if the response goes on for too long. Like a track racer running at a very high speed, the body begins to approach its physical limits, and the potential for exhaustion, breakdown and physical damage is increased.

If the response continues long enough, the body's changes begin to cause problems, as shown below.



-Increases serum glucose levels
-Increases water retention
-Increases free fatty acid release
-Increases blood pressure
-Suppresses immune responses
-Elevates level of amino acids in the blood
-Decreases capacity to maintain mood stability
-May prevent formation of new axonal connections in the brain
(Popoli et al., 2011); ( Gądek-Michalska et al, 2013)

These body changes are set in motion as part of a trade-off: the body sacrifices its long-term well being in order to use its energies to meet the challenges of the moment. Over time, this sacrifice sets the body up for a variety of stress related problems: high blood pressure, increased vascular plaque, increased illness, depression. Furthermore, recent studies seem to show that elevated levels of cortisol affect both serotonin mechanisms and the capacity of the brain to develop new axonal connections in the brain.

What these means in practical terms is that people under long-term stress can get "in a rut", where they can't use some of their most constructive and effective cognitive tools. The brain, in effect, can go into a mode of stasis, where new approaches to handling problems cannot physically occur - because the chemistry to form new ideas, solutions, and memories is prevented by the stress related chemicals in the brain.

When clients under stress report being stuck and feeling helpless, there is a chemical reason behind it. The body, under stress over time, may also bring into play two other mechanisms to help provide enough energy to meet the challenge of the moment.

The first is the use of Growth Hormone (GH), a chemical with many metabolic effects throughout the body. The primary role of GH is to help the body use fat as an energy resource. Growth Hormone also works to persuade the body to increase the uptake of amino acids by the cells. This affects how much glucose, or blood sugar, is taken up by the cells, and can increase blood sugar, and cause increased insulin release, causing problems similar to what happens with diabetes.

The harmful long-term effects of this chemical are shown below.



-Reduction in cellular glucose uptake, which may result in rise in blood sugar
-May produce insulin-resistance effects
-Influences retention of sodium, potassium, phosphate, and calcium in body
(McEwen, 2004)

The body has one final major component that is involved in stress response. This is the use of Thyroid Hormones to increase the general metabolic rate. The thyroid is a very small gland that has very important effects on a person's metabolism and energy level. When a stress response occurs for a long enough period of time, the thyroid will release its chemicals. The amount of chemicals released by the thyroid gland is very small, but the effects on the body can be very pronounced.

The long-term effects of the release of these chemicals is shown below.



-Increase in general metabolic rate
-Increase in heart rate
-Increase in heart contractibility
-Increase in peripheral vascular resistance

The body is designed to be willing to trade the future well-being of a person in order to maximize the chances of staying alive. In less modern times, when daily dangers were more likely to be truly life threatening, this was a sensible trade-off for survival. What has happened, though, is the body has had difficulties adapting fast enough to keep up with the changes in the challenges.

At the same time, life has gotten more complicated. While there are less likely to be constant challenges involving life threatening physical danger, there are often greater numbers of challenges. These challenges are still being perceived and evaluated with the same four levels of our evolutionary equipment: the four systems discussed in the first part of the training.

The tendency of the deepest parts of our perceptual and evaluatory systems to find life threatening events where none exist is a problem when so many - and so constant - challenges are present in our environment. It causes people to spend far too much time in the response phase of the five stage stress response, and too little time in the remission and recovery phases. This is the meeting point of all of the concepts that have been presented in this training so far. Let's review.

The body evaluates life's events with varying degrees of accuracy with different systems in different levels of the brain.

The body attempts to move through five stress stages designed to respond effectively, then quickly return the body to a more quiescent state, repair and reset itself to prepare for the next event.

Modern stresses are more continuous in nature, so the response phase continues, and the body has to bring in increasingly complicated response mechanisms, moving the person closer to a point of breakdown.

The news is not all bad, however. Because there are many factors involved in this current state of affairs, there are also many points of impact to help address the stress, and create the possibility of successful stress management.

This is where we will turn in the next section - taking what we have learned so far and applying that knowledge to a search for solutions.

Review Questions for Section V

At this point in the training, the trainee should be able to answer the following questions:

When scientists study the physiology of stress responses over time, they usually break down the stress responses into three phases. What are these three phases?

What chemicals become involved in the process of chronic stress and what are the destructive effects of these chemicals?

Which chemical involved in chronic stress is believed responsible for impairments in the formation of new brain connections?