Adrenal hormones constrict blood flow to the forebrain and stress hormones
repress the prefrontal cortex activity diverting energy and consciousness to the
hindbrain and survival faculties. Besides stress being enervating, prolonged
hypothalamic-pituitary-adrenocortical activation also makes us dumber. (See
General Adaptation Syndrome)
“The longer you stay in protection, the more you compromise your growth.” 147,
Bruce Lipton, The Biology of Belief.
General aDaPtation sYnDrome
The hypothalamus, though only about the size of a pea, is the director of
chemistry in the body. After having received input from the body it then transmits
instructions to the pituitary to release its various hormones. The hypothalamus
responds to stress by initiating the stress-hormone cascade starting with the
corticotrophin releasing hormone (CRH) followed by adrenocorticotropic
hormone (ACTH) release, and finally glucocorticoid production. A variety of
stressors, both physical and psychological, cause the neurosecretory cells within
the paraventricular nucleus of the hypothalamus to secrete corticotropin-releasing
hormone (CRH) and arginine vasopressin (AVP) into the microportal circulatory
system of the pituitary stalk. Cells in the hypothalamus which secrete CRH
have synapses which make contact with blood vessels in the hypothalamus that
transport CRH to the anterior pituitary where it stimulates the release of ACTH.
ACTH stimulates the hypothalamus (HPA axis) to immediately activate the
adrenal glands. From the adrenal glands the hormones epinephrine (adrenaline)
norepinephrine (noradrenalin) are secreted which vasodilate arterioles of the
skeletal muscles to prepare them for action, but cause vasoconstriction elsewhere.
This produces quicker heart rate, higher blood pressure, more frequent breathing.
Cortisol and cortisone suppress the immune system in an effort to conserve energy
for fight-or-flight. These glucocorticoids promote conversion of protein and lipids
to carbohydrates replenishing energy reserves in the body. Cortisol feeds back to
the hypothalamus to control release of CRH. There is a circadian (daily) rhythm
in ACTH secretion and cortisol levels which is higher in the morning and cortisol
is secreted in several ‘pulses’ during the day.
During stress the thyroid gland is stimulated by the thyroid-stimulating hormone
(TSH) to secrete thyroxine to increase metabolism. Gonadotrophins are secreted
which stimulate the reproductive glands to produce less hormones. The quantity
of each kind of hormones the pituitary will secrete depends on the power of the
stressor. The more life threatening the brain perceives the stressor to be, the more
the pituitary is stimulated. The pituitary responsiveness in hypothyroidism causes
adrenal dysfunction directly and results in hypersecretion of ACTH mediated by
increases in synthesis of CRH and Vasopressin in the hypothalamus.
The majority of people respond to stressors with activation of the sympathetic
system. When our HPA axis is chronically fired up, the stress hormones inhibit
and cell division and growth in the hippocampus and prefrontal cortex. Thus
our brain areas for rational thinking and memory atrophy and shrink leading to