Why zebras don't get ulcers: The acclaimed guide to stress, stress-related diseases, and coping-now revised and updated
By: Sapolsky, R. M. (2004).
New York: Henry Holt.
As the master gland, the brain can experience or think of something stressful and activate components of the stress-response hormonally.
Some of the hypothalamus-pituitary-peripheral gland links are activated during stress, some inhibited.
Two hormones vital to the stress-response released by the sympathetic nervous system:
- Epinephrine
- Norepinephrine
Acts within seconds
Another important class of hormones in the response to stress are called glucocorticoids.
These are steroid hormones secreted by the adrenal gland.
Back the epinephrine activity up over the course of minutes to hours.
Because the adrenal gland is basically witless, glucocorticoid release must ultimately be under the control of the hormones of the brain.
When something stressful happens or you think a stressful thought, the hypothalamus secretes an array of releasing hormones into the hypothalamic-pituitary circulatory system that gets the ball rolling.
The principal such releaser is CRH (coticotropin releasing hormone).
A variety of minor players synergize with CRH
Withing fifteen seconds, CRH triggers the pituitary to release ACTH (corticotrpin) in the bloodstream.
ACTH reaches the adrenal gland and (in a few minutes) triggers glucocorticoid release.
Together, glucocorticoids and the secretions of the sympathetic nervous system (epinephrine and norepinephrine) account for a large percentage of what happens in your body during stress.
In times of stress, your pancreas is stimulated to release a hormone called glucagon.
Glucocorticoids, glucagon, and the systematic nervous system raise circulating levels of the sugar glucose.
These hormones are essential for mobilizing energy during stress.
Other hormones are activated as well.
The pituitary secretes prolactin, which plays a role in suppressing reproduction during stress.
Both the pituitary and the brain secrete endorphins and enkephalins, which help blunt pain perception.
The pituitary secretes vasopressin (antidiuretic hormone), which plays a role in the cardiovascular stress response.
Various hormonal systems are inhibited during stress
The secretion of various reproductive hormones such as estrogen, progesterone, and testosterone are inhibited.
Hormones related to growth are also inhibited.
As are the secretin of insulin.
A few complications
Fight or flight response is a way of conceptualizing the stress-response as preparing the body for that sudden burst of energy demands.
This might be different in females.
In most species, females are typically less aggressive than males, and having dependent young often precludes the option of flight.
Some suggest that the female stress-response is about tend and befriend, taking care of her young and seeking social
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