The HPA Axis: Stress and Your Adrenals

We’ve established that the pituitary gland sends a signal to the adrenals to produce cortisol when there’s a perceived threat in the environment, right? Well, think of the pituitary as second in command. The master commander of the entire central stress response system is the hypothalamus.

It’s the hypothalamus that actually surveys the environment for any possible threats (real or imagined), and alerts the pituitary gland if a threat is perceived. The pituitary then signals to the adrenals to pump out cortisol (and if you’ve watched my Hormones 101 video, you know that hormones are considered “chemical messengers”). So the cortisol response serves as a messenger to the rest of the cells in the body to behave in a certain way, like we’ve already discussed.

When the hypothalamus becomes too vigilant and is constantly alerting the pituitary and adrenals to do their thing, the adrenals simply start ignoring the commands of the hypothalamus. This is an issue.

Perpetual activation of the HPA axis leads to overactivity, followed over time by underactivity. Which makes sense- once you’ve burned through your adrenal reserve, your once-hyperactive HPA becomes sluggish and fatigued. This leads to symptoms like exhaustion, increased likelihood of getting sick because the immune system is weakened, decreased sex drive, low blood pressure, and general malaise.

In a nutshell, this is how cortisol imbalance can swing from overall high cortisol levels (when the HPA is in overdrive) to very low cortisol levels- when the HPA and adrenal reserves are spent. This also explains how you might have symptoms of both high and low cortisol.