Posted by Elroy on June 21, 2005, at 18:13:48
In reply to Re: HPA Axis and Anti-Cortisol Therapy - MORE INFO » Elroy, posted by Elroy on June 21, 2005, at 18:06:56
http://www.nih.gov/news/pr/sep2002/nichd-09.htm
Very Good explanation....
QUOTE:
The HPA axis is a feedback loop by which signals from the brain trigger the release of hormones needed to respond to stress. Because of its function, the HPA axis is also sometimes called the “stress circuit.”
Briefly, in response to a stress, the brain region known as the hypothalamus releases corticotropin-releasing hormone (CRH). In turn, CRH acts on the pituitary gland, just beneath the brain, triggering the release of another hormone, adrenocorticotropin (ACTH) into the bloodstream. Next, ACTH signals the adrenal glands, which sit atop the kidneys, to release a number of hormonal compounds.
These compounds include epinephrine (formerly known as adrenaline), Norepinephrine (formerly known as noradrenaline) and cortisol. All three hormones enable the body to respond to a threat. Epinephrine increases blood pressure and heart rate, diverts blood to the muscles, and speeds reaction time. Cortisol, also known as glucocorticoid, releases sugar (in the form of glucose) from the body reserves so that this essential fuel can be used to power the muscles and the brain.
Normally, cortisol also exerts a feedback effect to shut down the stress response after the threat has passed, acting upon the hypothalamus and causing it to stop producing CRH.
This stress circuit affects systems throughout the body. The hormones of the HPA axis exert their effect on the autonomic nervous system, which controls such vital functions as heart rate, blood pressure, and digestion.
The HPA axis also communicates with several regions of the brain, including the limbic system, which controls motivation and mood, with the amygdala, which generates fear in response to danger, and with the hippocampus, which plays an important part in memory formation as well as in mood and motivation. In addition, the HPA axis is also connected with brain regions that control body temperature, suppress appetite, and control pain.
Similarly, the HPA axis also interacts with various other glandular systems, among them those producing reproductive hormones, growth hormones, and thyroid hormones. Once activated, the stress response switches off the hormonal systems regulating growth, reproduction, metabolism, and immunity. Short term, the response is helpful, allowing us to divert biochemical resources to dealing with the threat... Stress suppresses the reproductive system at various levels, says Dr. Chrousos. First, CRH prevents the release of gonadotropin releasing hormone (GnRH), the “master” hormone that signals a cascade of hormones that direct reproduction and sexual behavior. Similarly, cortisol and related glucocorticoid hormones not only inhibit the release of GnRH, but also the release of luteinizing hormone, which prompts ovulation and sperm release. Glucocorticoids also inhibit the testes and ovaries directly, hindering production of the male and female sex hormones testosterone, estrogen, and progesterone....
One of the major disorders characteristic of an overactive HPA axis is melancholic depression. Chrousos’ research has shown that people with depression have a blunted ability to “counterregulate,” or adapt to the negative feedback of increases in cortisol. The body turns on the “fight or flight” response, but is prevented from turning it off again. This produces constant anxiety and overreaction to stimulation, followed by the paradoxical response called “learned helplessness,” in which victims apparently lose all motivation.
Hallmarks of this form of depression are anxiety, loss of appetite, loss of sex drive, rapid heart beat, high blood pressure, and high cholesterol and triglyceride levels. People with this condition tend to produce higher-than-normal levels of CRH. The high levels of CRH are probably due to a combination of environmental and hereditary causes, depending on the person affected.... Other conditions are also associated with high levels of CRH and cortisol. These include anorexia nervosa, malnutrition, obsessive-compulsive disorder, anxiety disorder, alcoholism, alcohol and narcotic withdrawal, poorly controlled diabetes, childhood sexual abuse, and hyperthyroidism.
The excessive amount of the stress hormone cortisol produced in patients with any of these conditions is responsible for many of the observed symptoms. Most of these patients share psychological symptoms including sleep disturbances, loss of libido, and loss of appetite as well as physical problems such as an increased risk for accumulating abdominal fat and hardening of the arteries and other forms of cardiovascular disease. These patients may also experience suppression of thyroid hormones, and of the immune system. Because they are at higher risk for these health problems, such patients are likely to have their life spans shortened by 15 to 20 years if they remain untreated...
END QUOTEElroy
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