The HPA axis is the name given to the neuroendocrine system made up of the hypothalamus, pituitary gland and the adrenals. These three organs communicate with and regulate each other through the secretion of hormones to control the bodies adaptation to stress, digestion, the immune system, metabolism and mood. The hypothalamus can be thought of as the control center of the hormone system that exists in the brain, and releases CRH (Corticotropin releasing hormone) which communicates with the pituitary gland to cause it to releases ACTH (adrenocortiotropic hormone) that cause the adrenals to release cortisol all response to stress. The role of cortisol is preparing the body for activity by increasing energy available through raising blood sugar and increasing adrenaline (epinephrine/norepinephrine) release from the adrenals. As cortisol builds up in the body it inhibits the release of CRH from the Hypothalamus and ACTH from the Pituitary gland, which limits the further production of cortisol in what’s called negative feedback. It’s the bodies way of preventing excess cortisol from being produced and is one of the main checks and balances on the HPA axis. The process of CRH release from the hypothalamus which cascades into cortisol production from the adrenals is caused by: stress, physical activity, illness, the circadian rhythm. In healthy individuals the circadian rhythm causes a spike of cortisol within an hour or waking up, then declines rising again in the late afternoon and eventually declining at night in preparation for rest. This is how the body maintains appropriate cortisol levels for each period of the day, however in those with circadian rhythm dysfunction cortisol levels are either a flat line throughout the day or the spikes and declines happen at inappropriate times. For example, cortisol will be low in the morning and high at night, which manifests as waking up feeling fatigued and feeling wired at night. The HPA axis has a key role in regulating the heart, metabolic system, digestion, sexual hormones and the immune system. In essence the HPA axis is how a perception of the environment through the senses and interpretation by the brain lead to physiological changes that allow us to adapt to the needs of the environment. Why is this important to understand when we talk about mental wellness and the effects of chronic stress on the body? The HPA axis responds to chronic stress by constantly releasing cortisol, even at times when there is no true threat present and high cortisol levels directly suppress the immune system, and lead to dysfunction of memory, mood and lead to the imbalances that lead to a state susceptible to disease. It is very important to note that CORTISOL IS NOT BAD, it is a necessary survival function that allows us to adapt to the environment and can be extremely useful for generating the energy that allows us to increase focus and take action when needed. However, unchecked high levels of cortisol eventual lead to the HPA axis dysfunction When high levels of cortisol are continually present the organs of the body begin becoming tolerant of this hormone and reacting less to tit’s signals, requiring more cortisol to achieve effects. If you continue this process to the end of dysfunction eventually the whole system is unable to produce enough cortisol or control level changes and conditions such as chronic fatigue syndrome, insomnia (from dysregulation of HPA axis) and overall burnout aka “adrenal fatigue”. This is level 3 of the stress response where there is simply exhaustion. In level 1 the system functions normally, a stressor is perceived the HPA axis is activated, physiology changes to adapt to the stress and the stress goes away and cortisol naturally lowers back to a normal state. In level 2 of the stress response there is an overstimulation of stress, so cortisol levels remain high and the body is in a constant state of fight or flight. This is chronic anxiety, restlessness, and just feeling always on edge. When it reaches level 3 stressors have little effect, and there is just apathy and exhaustion. Many antidepressants are thought to function by their effects on helping balance the HPA axis or reduce the damaging effects of stress and increasing resistance, as well as numerous herbs such as those in the adaptogens class. A classic example is the herb Ashwagandha, which has been shown to have a beneficial benefit on balancing the HPA axis, and balancing cortisol responses to stress. There are a variety of other Hypothalamus-Pituitary-Organ systems such as the HPT (Hypothalamus-Pituitary-Thyroid) axis which balance thyroid functioning and the HPG axis (Hypothalamus-Pituitary-Gonadal) which balance sexual functioning. The hypothalamus-pituitary systems are the way the nervous system and hormonal systems interface to produce the adaptability to the human to changes in the internal and external environments.
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