The Endocrine system controls a plethora of physiological aspects in humans and other higher organisms, including metabolism, reproduction, and reactions to stress. The various organs and glands within this system cooperate to ensure the effective functioning of the organism through various pathways. One such pathway is the Hypothalamic Pituitary Adrenal Axis.
The Hypothalamic Pituitary Adrenal Axis is a mechanism that prepares our bodies to take on a stressful situation. This system monitors various chemical levels inside our bodies and adjusts hormones accordingly while operating across multiple organs and glands. Below we investigate how this system works, the major organs, hormones, and glands involved, and issues relating to the dysfunction of this Axis.
Understanding The Hypothalamic Pituitary Adrenal AxisComplications Of The Hypothalamic Pituitary Adrenal AxisConclusions
Understanding The Hypothalamic Pituitary Adrenal Axis
Complications Of The Hypothalamic Pituitary Adrenal Axis
Conclusions
The Hypothalamic Pituitary Adrenal Axis (HPA) is an intricate part of humans' and other mammals' coping mechanisms during high stress. When presented with a stressful situation, theAxis acts together to release cortisol into the body, preparing it for high-intensity activities over a long time.
These stresses are fromphysical and emotional sources. The HPA is a fundamental part of the endocrine system. This process isnot time-dependent, so the Axisinvolves hormones, which take a longer time to work than nerves but persist for longer.
Theendocrine systemis a fascinating part of human anatomy, with the pituitary gland and the hypothalamus taking front and center stage.
There are severalmajor “role players” in the endocrine system, including:
Due to the sheer size of the endocrine system,various subdivisions and pathwayscontrol various reactions and processes. One of these pathways is the Hypothalamic Pituitary Adrenal Axis.
What Is The Hypothalamic Pituitary Adrenal Axis’s Function?
Theprimary functionof the HPA is tostimulate the adrenal glands to produce cortisol. Aside from this function, the HPAregulates other aspectsof the organism’s physiology to promote homeostasis during stress-inducing situations.
Maintaining homeostasisis critical to ensuring the optimal functioning of an organism.
To this extent, the Hypothalamic Pituitary Adrenal Axis plays a role. The HPA is fundamentallythe interactionsbetween thehypothalamus, pituitary gland, and adrenal glands, particularlyduring stress-inducing events.
Theend goalof this pathway (and these interactions) ofproducing cortisolis to prepare the body for a“fight or flight” situation. This preparation includes providing the body with sufficient energy for an extended duration.
TheHPA alters behavioral and physiological componentsof the organism (e.g., human) to ensure that the organism hasall the tools requiredto survivethe stressful situation it is currently facing.
The Hypothalamic Pituitary Adrenal Axis: Location, Composition, And Operation
Theessential componentsof this Axis include:
The hypothalamus is adiminutive but critical region of the brain, located towards the base, where the optic nerves crossover at the optic chiasm.
The hypothalamusreleases Corticotropin-releasing hormone(CRH), an essential hormone for dealing with emotional and physical stress.
Furthermore, the hypothalamus directly controls/influences appetite, blood pressure, sleep, temperature, and water balance in the body.
The Pituitary gland is adjacent to the hypothalamus and is responsible for much of theendocrine system, although only the size of a pea on the brain’s underside. This gland is split into two parts, theanterior (adenohypophysis)and theposterior (neurohypophysis).
Theanterior pituitary glandaccounts for roughly 80% of the total size. Some of thehormones producedhere include:
These hormonestarget specific organsand elicit the desired responses in the body.
Once the hypothalamus secretes Corticotropin-releasing hormone, the pituitary gland beginssecretingadrenocorticotropic hormone(ACTH), which moves towards the adrenal gland on top of the kidneys.
Once the pituitary gland releases ACTH, the adrenal glandsbegin producing corticosteroidhormones andepinephrine. Once released into the bloodstream, these hormonesmaintain blood pressure, affect theheart rate, and regulatemetabolism.
The adrenal glands arepositioned one per kidneyand divided into two sections. Theinner adrenal medullaand theouter adrenal cortex. They operate under the influence and control of the pituitary gland and hypothalamus, among others.
Theadrenal cortexis further divided intothree regions: the zona glomerulosa, zona fasciculata, and zona reticularis.
Each of these zonessecretes specific hormones, but our focus is on one in particular:
It is also responsible for suppressing inflammation, increasing blood sugar, and decreasing bone formation. This glucocorticoid is critical during stressful situations as it assists your body in “managing” its resources.
Although the Hypothalamus, Pituitary gland, and adrenal glands are the major role players in the Axis, they would be ineffective without theconnecting tissues and systems. Thenervous,lymphatic, andcirculatory systemsare critical to the proper functioning of the HPA.
How Does The Hypothalamic Pituitary Adrenal Axis Work?
The HPA comes into effectduring stress-inducing incidents.
When youfirstexperience stress, your body releasesepinephrine (adrenaline)andnorepinephrine(noradrenaline). These stress hormones increase the heart rate and metabolism. They also cause you to perspire more, among other physiological changes.
Thesympathetic nervous systemcontrolsthe secretion of these hormones and works in conjunction with the adrenal glands. These stress hormones are related to theadrenal medulla.
After roughly10 secondsof these increased norepinephrine hormones, the Hypothalamic Pituitary Adrenal Axis “activates.”
Thehypothalamusregisters the increased stress hormones and beginssecreting Corticotropin-releasing hormone(CRH) (andArginine Vasopressin(AV)).
Once secreted, thepituitary glandrecognizes the CRH and AV via dedicated receptors (CRH-R1 and V1B receptors). Theanterior pituitary glandbegins producing andreleasing Adrenocorticotropic hormone(ACTH) (the increase in CRH also systematically enhances the sympathetic nervous system’s functioning).
After diffusing into the blood, theACTH moves to the adrenal glands. The ACTH targets theadrenal cortexat the adrenal glands, the area responsible for producingsteroid hormones(glucocorticoids).
The adrenal cortex “picks-up” the ACTH through the type 2 melanocortin receptors (MC2-R) and beginssynthesizing cortisol.
Cortisol is themost significant corticosteroidin the human body, and it works on several organs and systems toprepare the bodyfor stressful situations.
Once released,cortisol stimulatestheliverto release its glucose store, regulatesblood pressure, andassists the bodyin using carbohydrates, proteins, lipids, and other dissolved nutrients through various processes, including lipolysis, proteolysis, enhancing vasoconstriction, suppressing reproduction, and alter certain behaviors related to stress.
This suppression and heightening of certain processespromote homeostasiswithin the body.
This increased blood glucose, and better control of the body’s resources, provide the body withsufficient energyto cope with the stressor.
What Is The Benefit Of The Hypothalamic Pituitary Adrenal Axis?
During stress-inducing events, our bodies produce various hormones that prepare us for action. Thesehormones push our bodiesout of a state of homeostasis.
The Hypothalamic Pituitary Adrenal Axis(HPA) helps to regulate and mitigatethe effects of thesehormonesin our bodies, reducing the amount of deviation from the point of equilibrium.
Thehypothalamus and pituitary gland “sense” the cortisol(and other hormones) levels in the body and increase the amount of CRH and ACTH in the blood. This regulatory functionmaintains the organismduring a state of stress, ensuring that functions benefiting survival are prioritized.
The hypothalamus and pituitary glands' constant monitoring of hormone levels is called a“negative feedback loop.”
This loop serves a vital dual function. TheHPA maintains the cortisol levelsduring the “crisis.” It furthertells the body to “switch off”the stress response.
The HPA allows theorganism to function at optimalin the “heat of the moment,” with the best chance of survival, while other “less important” bodily functions are reduced.
Stress is atypical partof any animal’s life, and havinga dedicated system to deal with stressmeans that we are built to handle most types of stress.
Thenegative-feedback loopassociated with the HPAprotects the bodyduring extended periods of exposure to cortisol and other stress hormones.
There are certainnormal consequencesto activation of the HPA, including:
Theintensity and durationof the glucocorticoid’s presence in the bodyimpact the normaland effective operation of the HPA.
Although human bodies are designed to cope with stressful situations through mechanisms like the Hypothalamic Pituitary Adrenal Axis (HPA), it is not always withoutcomplications, limitations, and drawbacks.
Some of thecomplications related to the HPA include:
Most of the negative effects are due tochronic exposure to the HPA (and cortisol). A considerable drawback with the HPA is that youdon’t have to be in a life or death situationfor it to activate.
If you’re in adifferent type of stressful situation(pressure from work or the family) or if you’re experiencinganxiety, theHPA may be stimulatedinto action.
Prolonged exposureto elevated cortisol levels results in the body’sbaseline cortisol level increasing. This increase means that your body isconstantly under a state of fatigue, and when a situation arises for “fight or flight,” yourbody is less well adaptedand prepared to deal with it.
An example of this isChronic Fatigue Syndrome.
Aside from reduced effectiveness in using cortisol, thecortisol levels may take longerto come down after a stressful incident.
Substance abuse(like alcohol) is also linked toaffecting effective HPAfunctioning.
The Effects Of Chronic Exposure To The Hypothalamic Pituitary Adrenal Axis
Chronic exposureto the HPA results in:
Somecommonly identified disordersrelated to prolonged cortisol exposure include:
Developmental Issues Of The Hypothalamic Pituitary Adrenal Axis
Aside from chronic exposure to the HPA,abnormalities of the HPA might establish during fetal development, which persists into adulthood, including:
Symptoms Of Dysfunction In The Hypothalamic Pituitary Adrenal Axis
Whether through chronic exposure, intensive exposure, or some other dysfunction, the Hypothalamic Pituitary Adrenal Axis(HPA) may become dysfunctional.
Some of the symptomsof a dysfunctional HPA include:
Treatment Of Hypothalamic Pituitary Adrenal Axis Issues
The best way to ensure optimal functioning of the HPA isthrough prevention. Ahealthy lifestylereduces stress and includes ahealthy diet, reducing (or stopping)caffeine and alcoholintake, properexercising and sleepregime, andrelaxationtechniques.
Psychotherapy, counseling, andbiomonitoring tools(like heart rate monitors, blood sugar indicators, etc.) are other methods many people use in controlling HPA dysfunctions.
However, prevention is not always possible, and in situations where there is already the onset of disease,medication is often necessaryto control the symptoms/treat the disease.
Thetable belowexaminessome diseasesrelated to HPAdysfunctions and their treatment methods.
HPA DiseaseTreatmentMedicationAnxiety and depressionMedication (antidepressants) and lifestyle changesProzac, Zoloft, Paxil, Lexapro, and CelexaChronic Fatigue SyndromeTherapy (CBT), antidepressants, and lifestyle management. Treatment is tailored and treats symptoms.Amitriptyline, over-the-counter headache tablets.Cushing’s diseaseMedicationketoconazole, mitotane (Lysodren), and metyrapone (Metopirone)PTSDCognitive-behavioral therapy (CBT) and medicationparoxetine and sertraline
Although in some situations, medications are essential for treating HPA-related conditions,aholistic approach is best(i.e.,removing orreducing the root causeof the problem, not only treating the symptoms.
The Hypothalamic Pituitary Adrenal Axis (HPA) is an essential part of the endocrine system, tasked with controlling the “fight or flight” response many mammals (humans included) experience. By increasing and decreasing the hormonal cocktail inside the organism, this Axis readies the organism for a high-stress situation. However, chronic exposure to cortisol, the primary glucocorticoid linked to this HPA, has some drawbacks, including mood disorders, anxiety, and stress-related pathogens and diseases.
References
https://www.karger.com/Article/Abstract/216184
https://www.frontiersin.org/articles/10.3389/fnbeh.2020.601939/full
https://www.simplypsychology.org/hypothalamic%E2%80%93pituitary%E2%80%93adrenal-axis.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3580872/
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