We’ve all experienced that moment of being suddenly thrown into a state of dread. Or panic. Or even just had the daylights scared out of us. It’s that universal feeling of racing heart, sweat suddenly pouring from your pores, and your limbs feeling like they’ve turned to jelly. (Unless you’re a psychopath, but that’s a whole separate article).
This is your body’s reaction to a “threat” — preparing you to fight or run. For most, it’s an unpleasant feeling, but an infrequent and usually short-lived one. Once the “threat” has passed, your heart rate and breathing return to normal and your sweat glands chill the hell out.
How The HPA Axis Helps You Fight (Or Run From) Tigers
This reaction is the work of a part of your body called the hypothalamic-pituitary-adrenal axis, or HPA axis. The primary function of the HPA axis is to regulate your body’s stress response. The word “axis” refers to the interplay between the hypothalamus, the pituitary gland, and the adrenal glands (HPA. Get it?).
The three parts of the “axis” are all connected and working together. The first two, the hypothalamus and the pituitary gland, are in your brain, right above your brainstem. The adrenal glands sit on top of your kidneys.
That elevated heart rate thing happens almost instantly. That’s your sympathetic nervous system secreting epinephrine and norepinephrine, each contributing to an increased heart rate and perspiration. The norepinephrine is also responsible for waking up your HPA axis — which takes about 10 seconds — sparking your hypothalamus, pituitary gland, and adrenal glands to action. The hypothalamus releases corticotropin-releasing hormone (CRH), which tells your sympathetic nervous system to keep that heart rate up.
The CRH from the hypothalamus communicates to the pituitary gland to secrete adrenocorticotropic hormone (ACTH) into the bloodstream. The ACTH then travels from the pituitary gland (right above the brainstem, remember?) down to the adrenal glands.
And the adrenal glands secret that much-maligned hormone we all love to hate: cortisol.
The HPA Axis And Cortisol — The “Stress Hormone”
Following the initial activation of the HPA axis, cortisol is released for several hours. Once a specific concentration of it has built up in the blood, the cortisol sends a message back to the hypothalamus to chill the fuck out. “We’re good,” your cortisol-filled blood tells your brain. “No actual tigers to fight here — you can stop releasing cortisol now.” And the body returns to its baseline state, or “systemic homeostasis.”
You can think of your HPA axis as your body coiling like a spring, preparing to use the potential energy it’s saving up. Cortisol is a hormone that puts you on alert, wakes you up, literally. Though it’s known for being the “stress hormone,” cortisol is largely responsible for the maintenance of your daily sleep-wake cycle — your circadian rhythm.
Cortisol increases your blood pressure, pushing your heart to pump more blood to your muscles in case you have to run. It increases glucose levels in your blood, providing additional energy to your cells to help you deal with the stressor. Cortisol is a necessary and useful part of being a human being.
Until it isn’t.
What Happens With Repeated, Ongoing Activation Of The HPA Axis?
Cortisol may be responsible for necessary functions like sleep and helping us react to stressful situations, but it also causes other, less desirable things to happen in our body. It decreases reproductive activity. Ever heard of stress causing infertility or even causing a person to miss their period? Yup. That’s cortisol. It’s the body concluding that external stressors are too great to also deal with the additional stressor of supporting a pregnancy or caring for offspring. Wild, right? And also, that sucks. Because … infertility is stressful. It’s a vicious cycle.
Repeated HPA axis activation can also lead to a suppressed immune system. Same issue here — if your body needs to worry about an immediate threat like a tiger trying to eat you, your body can’t be bothered with trivial things like preparing itself for a potential future infection.
And, though scientists aren’t sure of the mechanism, there is a correlation between ongoing high levels of cortisol and type 2 diabetes, obesity, and cardiovascular disease. The thought is that the triggering of increased glucose in the blood by the HPA axis likely has something to do with these outcomes.
Stressed the fuck out and suddenly your memory has gone to shit? HPA axis/too much cortisol. Again, what’s the point of remembering stuff if you’re not capable of outrunning that tiger? Remembering where you put your glasses is irrelevant if you’re tiger dinner. Depressed? Yup, your HPA axis — and the cortisol it keeps pumping out — is probably contributing to that, too.
And now scientists believe that early childhood trauma — i.e., repeated activation of the HPA axis in childhood — can lead to a more reactive HPA axis in adulthood. If you experienced a lot of childhood trauma, your heart rate may have just increased with a feeling of “Oh shit, that explains some things.”
Why Does This Matter To Know?
For those of us who are unraveling childhood trauma or dealing with current, ongoing stressors, it may be tempting to conclude that our overreactive HPA axis is a kind of prison sentence. If our bodies are suffering through this ongoing onslaught of cortisol instantly and involuntarily, what does it help to know how it works? It’s not like we can help it. Yeesh.
But consider this: When we think about reducing the stress in our lives, our goals are often reactionary. How can I respond differently to XYZ trigger? How can I react more calmly to this known repeated stressor? How can I calm myself down after XYZ trigger has led to a panic attack?
We’re reactive. But given that the HPA axis only needs about 10 seconds to get into full cortisol-pumping mode, and once it’s taken off, there’s not a whole lot you can do to stop it, reacting is only going to help so much. So be proactive. Set boundaries with people and situations that cause your HPA axis to go haywire, aka, stress you out. Unfriend, limit contact, cut out toxic people, and stop agreeing to show up for things that stress you out just because you’re trying to please others.
You’re allowed to protect your own peace.
Meanwhile, scientists are continuously working on therapies to help people who have an overreactive HPA axis. Some of us take antidepressants that increase serotonin levels, which studies show helps our body manage cortisol levels. Some studies are showing that EMDR therapy may decrease the reactivity of the HPA axis and the resulting flood of cortisol.
You do not have to live in a constant state of HPA axis reactivity. It’s okay to set boundaries. It’s okay to seek help. You deserve peace.