The HPA-Axis: What You Need to Know
The adrenal glands are a part of the HPA-Axis (Hypothalamic-Pituitary-Adrenal Axis).
How does the HPA-Axis really work?
If you're reading this, chances are you've read an article on adrenal fatigue. Maybe you think you have adrenal fatigue because you don't feel your best. You're constantly feeling fatigued, tired, and drained. However, the idea of "adrenal fatigue" is not 100% accurate. This leads us to the question, "what is really going on?"
The HPA Axis is made up of three parts - the hypothalamus, pituitary gland, and adrenal cortex. The hypothalamus is found in your brain. It's considered the master regulator of your body. It regulates things like temperature, blood volume, blood temperature, appetite, libido and it even regulates hormones in your body by communicating with the pituitary gland.
The pituitary gland makes several pre-hormones such as TSH (thyroid-stimulating hormone). It also makes a hormone to tell the adrenals to create cortisol.
The hypothalamus receives and analyzes information from the body. One piece of information being hormones. It can either increase or decrease the number of hormones being produced by the pituitary. It also analyzes information from your immune system.
The hypothalamus produces CRH (corticotropin-releasing hormone) which it sends to the pituitary gland. When the pituitary gland receives CRH from the hypothalamus it makes ACTH (adrenocorticotropic hormone).
ACTH then binds onto receptors on the adrenal cortex, which causes the adrenal glands to produce cortisol.
What is Cortisol?
Cortisol is a hormone produced by the adrenal glands. It belongs to a class of hormones called glucocorticoids, which affect almost every organ and tissue in the body. Cortisol's most important job is to help the body respond to stress.
Among its other tasks, cortisol helps maintain blood pressure and cardiovascular function, helps slow the immune system’s inflammatory response, helps balance the effects of insulin in breaking down sugar for energy, and helps regulate the metabolism of proteins, carbohydrates, and fats.
We all produce this hormone at baseline levels. It follows a circadian rhythm. This means cortisol levels are the highest right when we wake up and the lowest right after we fall asleep.
Under stress (emotional, mental, physical, anytime we perceive a challenge to the body), you will produce more cortisol. This release of cortisol will override the natural baseline levels of cortisol we're already producing. (That's a lot of cortisol).
When stress is received, flight or fight response is activated as part of the sympathetic nervous system. And because it's the nervous system, these reactions can happen within seconds. Whatever you need to deal with an immediate threat. Cortisol comes in as the next layer. It takes a little bit longer than the fight or flight response (minutes to hours, or even days and months). It responds to stress in a few ways:
Increases gluconeogenesis
Mobilizes fatty acids from adipose
Breaks down stored proteins
Enhances SNS response
Puts breaks on inflammation/immune system response
These all sound great, right? Well, not when the stress becomes chronic.
What are the negative effects of increased cortisol levels over time?
Alters perception and emotion in the Central Nervous System (CNS)
Suppresses reproductive function (you see this in female athletes when they lose their period from putting their body under extreme physical stress over time)
Suppresses growth hormone (GH) release
Suppresses thyroid-stimulating hormone (TSH)
Increases insulin resistance
Inhibits bone remodeling
The adrenal glands are end organs. They simply do what they're told to do.
The concept of adrenal fatigue is that your adrenal glands aren't making cortisol. Why could this be? They could be worn out, tired, fatigued. However, this is EXTREMELY RARE. Here are some other reasons:
There may be certain hormones, neurotransmitters or immune system molecules telling your hypothalamus not to produce CRH (inhibiting the production of CRH).
If the hypothalamus is not making CRH, the pituitary gland is not getting the input impulse to make ACTH. This means the adrenal glands don't receive it therefore it won't be signaled to make cortisol. Another reason is that the ACTH receptors on the adrenal glands may be blocked due to high inflammation, bacterial infections, etc. This is because the immune system molecules might be binding to the ACTH receptors instead
