What is the HPA Axis?
Updated: Jan 3
The Hypothalamic Pituitary Adrenal Axis, commonly known as the HPA Axis, is a cluster of endocrine organs in the body that work together to facilitate the release of….you guessed it….cortisol! You probably know the adrenals as the gland involved in the mechanism of stress, and if overworked can get ‘fatigued,’ out of balance, and further distract our “Symphony of Hormones” and overall body function.
There is no denying that the HPA-Axis is a trendy axis in the body to talk about due to its sheer impact it takes on in our fast paced, stressed out, modern world. The silver lining is there are many things we can do to prevent and heal imbalances to the HPA- Axis, which equips us with empowering knowledge to support our body, so that we can be the highest powered version of ourselves.
In this article, we will discuss what exactly the HPA- Axis is, so that when you hear all the ‘to-do’s’ on how to support it, you will know what in the world you are supporting, and the actual impact you have.
First, let’s break down the 3 parts of the HPA- Axis:
1. The Hypothalamus
The hypothalamus is a small organ in the brain, about the size of an almond, which conducts the functions of the endocrine and nervous systems (neuroendocrine function) through the Pituitary gland. Essentially, it is the Boss of the Pituitary! The Hypothalamus' major role is to ensure the body maintains homeostasis, and does so by first receiving internal and external stimuli from the body, such as light (to control circadian rhythm), low or high circulating thyroid hormone (to control the function of thyroid), and in the case of the HPA-Axis...stress (!!!), ultimately to protect us from harm.
When the Hypothalamus receives such stimuli, it then secretes a specific “releasing hormone” to the Pituitary gland to tell it to “release,” or secrete a further specified hormone to act on various areas of the body, and ultimately fix the stimuli that was originally sensed. The hypothalamus is one of the main conductors of our hormone symphony, and truly strives to protect our body’s by keeping it in balance...but despite this beautifully designed mechanism...imbalances can occur (or else we wouldn’t be talking about it, right?).
In regards to the HPA- Axis, the Hypothalamus is receiving stimuli in the form of stress. This can be internal stress (e.g infection, poor sleep, negative thoughts, fear, etc.) and/ or external stressors (e.g excessive exercise, inflammatory foods, traumatic life event, etc).
The key thing to know is the hypothalamus treats all stress the same! It’s got too much of an important role in the body to worry about what kind of stress is happening. Stress is stress is stress! Stress in any form (can’t stress this enough) will activate the HPA Axis pathway of cortisol production.
2. The Pituitary
Next in line in the HPA- Axis is the Pituitary, a Pea shaped gland situated right below the hypothalamus in the Brain, which it basically takes direction from all day long. While it constantly takes command, it is a critically important gland in the body, known as the “Master Endocrine Gland” due to its vast functional impact on the thyroid, adrenal, ovary and testes- some important stuff!
Based on a specific “releasing hormone” from the Hypothalamus, the Pituitary then releases another specific hormone into the bloodstream to travel to a specific organ in the body.
In the case of the HPA Axis, the Pituitary is receiving corticotropin- releasing hormone (CRH) from the Hypothalamus. Cortico= of the cortex (ie. outer layer of an organ/ gland), and tropin= to target another endocrine gland, so basically the Hypothalamus is saying, “We need to activate an organ/ gland to release cortisol due to the stress I'm sensing. Let’s get going or else this body is going to crumble.” So the Pituitary receives the CRH and then further specifies that signal and releases adrenocorticotropic releasing hormone (ACTH). Adrenocorticotropic= specific to the adrenal cortex. ACTH goes into the bloodstream, straight to the Adrenals!
3. The Adrenals
The infamous Adrenal Glands (plural for 2), are small triangular shaped glands located atop both kidneys, kind of like little hats. They are notorious for responding to stress with the hormone Cortisol, but also take part in releasing hormones to regulate the blood pressure (Aldosterone) and androgen/ sex hormone function (DHEA and Testosterone, which feed into female hormones of Progesterone and Estrogen.) It is important to note that an imbalance in one function of the Adrenals, like overproduction of Cortisol, can effect other functions of the Adrenals, like sex hormone function. Balance is important here, and we can consciously take part in that!
The Adrenals are the last in line within the HPA-Axis. They receive the ACTH from the Pituitary and immediately produce and release the glucocorticoid hormone, Cortisol. Glucocorticoids are simply steroid hormones, produced in the adrenal cortex, that have the ability to increase blood glucose. The fact that cortisol can increase our blood glucose levels is a survival mechanism to provide energy to the body to “run away from that tiger.” But, how often are we running away from tigers these days? ...that's a question for the Hypothalamus. "All day long, because I see all stress the same!" the Hypothalamus responds.
The HPA- Axis Pathway.
Now that we know the individual parts, let’s put it all together:
Step 1: Stress is perceived by the Hypothalamus, which sends CRH (corticotropin releasing hormone) to the Pituitary gland.
Step 2: The Pituitary receives CRH and quickly turns around and releases ACTH (adrenocorticotropic hormone) into circulation, to target the Adrenals.
Step 3: The Adrenal Glands receive ACTH and in turn produce Cortisol, to provide our body with the changes needed to respond to stress.
Step 4: One of the many processes the Hypothalamus surveys is the concentration of circulating Cortisol. The Hypothalamus senses when levels get too high, and then shuts down the pathway. This is known as a negative feedback loop, and yet another protective mechanism our body has.
In future blog articles, we will dive deeper into systemic actions of Cortisol, specific perceived stressors, adrenal gland adaptations (ie adrenal fatigue), and actionable nourishment you can apply to support optimal functioning. Until next time!