Stress : Part 1 - The Culprits

Stress basically refers to the changes in the body which prepares itself to react to certain cirumstances. It is also referred to as the "fight or flight response". It is termed so, because the reaction of the body prepares you to either fight the stimulus (that caused the stress), or flee from it before it can cause any harm. (This theory is from an example of a person under attack by an animal - like a bear)

Stimuli which cause stress are reffered to as stressors. Stressors can be external (traumatic or psychological) or they may be internal (infections or inflammations). Stress can be classified as Acute (short-term or fight-flight response) or Chronic (long-term) stress. After an acute stress response, the body changes reverse and returns to normal (relaxation response). Chronic stress is a response to on-going long-term stress situations which do not require a fight or flight response (for example, stressful work environment or stress due to marital problems).

In response to an acute stress, the body releases certain hormones and neurotransmitters. Basically, the response to any stress involves the hypothalamic-pituitary-adrenal axis (HPA axis).



A little briefing on what the above three mentioned are:

~ Hypothalamus - is a region in the brain which helps regulate body functions, providing a link between the nervous system and the endocrine system. It secretes releasing hormones (RH) in response to stimuli, which control the release of hormones by the pituitary gland.
~ Pituitary gland - a gland located at the base of the brain which releases hormones (that regualte a wide variety of body functions) in response to RH from hypothalamus.
~ Adrenal gland - gland situated above the kidney, and regulates stress by synthesis and release of catecholamines and corticosteroids.

So basically what happens is, when you are under stress your hypothalamus gets stimulated to secrete Corticotropin-Releasing Factor (CRF). The CRF acts on the pituitary gland and hence Adrenocorticotropic Hormone (ACTH) is realeased. The ACTH stimulates the adrenal glands to release Catecholamines and Corticosteroids (glucocorticoids - cortisol).

All the changes that occur in the body during stress are primarily due to release of catecholamines and cortisol. The major catecholamines are epinephrine, norepinephrine and dopamine. The catecholamine which plays the key role in stress related changes is epinephrine, also known as adrenaline (the stress hormone).

One of the effects of these hormones is on the amygdala - a region of the brain which manages emotions. In this case, it would cause fear. The hormones also signal the hippocampus (the region of the brain which is responsible for long-term memory), to store this experience for further reference. It helps to identify the same experience as one of fear/terror when you come across it again in the future. Also, the frontal brain (the front portion of the brain responsible for short-term memory, concentration, inhibition and rational thinking) is inhibited during a stress response. Hence, it can hinder the ability of a person to make rational/complex decisions and to concentrate (especially during exam stress).

Chronic stress on the other hand has very devastating and harmful effects on the brain and the rest of the body. During chronic stress, the body detects small levels of stress and keeps the nervous system slightly elevated causing release of stress hormones in extra amounts over a prolonged period of time. Studies have shown that chronic stress results in a shrinkage of the hippocampus with reduced blood supply, and hence causes a reduced acticity. Also, it is found that the amygdala increases in size and remains hyperactive, regardless of the stimuli.

The result of a shrunken hippocampus and an enlarged amygdala is not good. The huge amygdala causes anxiety and fear to even very small stimuli. The shrunken and inactive hippocampus makes it diffcult for you to process and recall the intial or the specific stimuli that caused your stress. Hence, the body will remain confused as to the specific cause of stress/fear/anxiety. The result will be that your body will stimulate the amygdala to cause generalized anxiety and fear.

In the next post, I will discuss specific changes in the body in response to stress.