Posted by Kath on June 13, 2000, at 15:38:22
In reply to Re: To Cam-Always a depressive? . » Kath, posted by Cam W. on June 12, 2000, at 11:03:22
Cam - Thanks SO MUCH! I love to understand things & I'll have to read this over a few times to get it clear, but this is so useful for me. I'm thinking of you all today & my prayers are with you. Thanks for answering my question.
Warm thoughts - Kath
Kath - The HPA (hypothalamus-pituitary-adrenal) axis is the body's stress response mechanism. It normally works in a cycle:
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> The body is stressed (psychologically or physically) and this causes the hypothalamus to produce and secrete CRH (corticotropin releasing hormone). The CRH is secreted into a localized blood supply system between the hypothalamus and pituitary (hypophyseal portal system) and, with help from vasopressin, stimulates the anterior pituitary to produce and secrete ACTH (adrenocorticotropin hormone) into the body's blood circulatory system. The ACTH travel to the adrenal glands (atop the kidneys) and stimulates the adrenal glands to produce and secrete cortisol into the bloodstream. The cortisol goes to various body organs initiating the body's "flight or fright" responses (eg decreased energy to the digestive system, increased energy to muscles and attention). The cortisol also travels to the hypothalamus and pituitary in a biofeedback mechanism, shutting off (or slowing) the flow of CRH and ACTH.
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> The above occurs under normal conditions. In depression, researchers have found that the biofeedback mechanism has broken down and CRH and ACTH are produced and secreted in an uncontrolled manner. The body tries to regulate this, but ends up manifesting as the symptoms we call depression.
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> Where neurotransmitters (like serotonin, norepinephrine, dopamine, GABA, the amino acids, etc.) come mainly into play is in the regulation of the responses of the hypothalamus and pituitary. Through complex interactions and wiring (which I still can't fully visualize - damn!) the raphe nuclei (serotonin), the locus ceruleus (norepinephrine), and the basal ganglia/limbic system (dopamine) all try to counter the effects of the excess cortisol release [due to increased ACTH causing (or because of) the feedback mechanism breakdown]. The neurotransmitter receptors located on various brain structures and on neurons that control or regulate other neurons are stimulated or inhibited in response to these changes. Over time these changes cause the concentrations of one or more of the neurotransmitters and/or concentrations of the various receptor sub-types to be changed (possibly resulting in the observation that serotonin levels are decreased in many people who have depression).
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> (I think this is mostly correct, hopefully someone will fix any blunders I have made.)
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> The HPA axis works, in short by:
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> Stress causing the hypothalamus to release CRH which causes the pituitary to release ACTH which causes the adrenals to release cortisol which goes to various organs initiating the "flight or fright" responses and also cortisol travels back to the hypothalamus and pituitary to shut off the output of CRH and ACTH, respectively.
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> Depression is a result of a break down in this shut off and can possibly be initiated by a malfunction at any point in the chain.
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> Hope this is clear - Cam
poster:Kath
thread:36729
URL: http://www.dr-bob.org/babble/20000610/msgs/37189.html