At any given time of day, there is a constant cascade of chemical reactions occuring within the human body. These reactions can be caused by numerous stimuli, including foods consumed, thought patterns or physical demands placed on the body. These reactions can be categorised into many different types of reaction, and two of such classifications include homeostatic responses, in which the body maintains balance of all biological parameters, and stress responses, where reactions of the body are in reaction to the introduction of an external stressor.

As with all biological systems, there are a large number of highly intricate mechanisms to detect, correct and balance substance and activity levels throughout the body. These systems are multi-faceted and constantly interact with other systems; in this sense, homeostatic and stress responses do not differ.

However, homeostatic responses deal with maintaining balance around the body, mainly through hormones. These are proteins that act as chemical messengers at their specific target tissue. Homeostasis is controlled primarily by the hypothalamus, a gland within the brain that is constantly sensing hormonal levels of the blood to ensure the levels are correct to maintain the correct rate of heat production, water balance and cellular activity. From this point, messages are sent a short distance to the pituitary gland, which acts as a director by manufacturing and then releasing its own hormones that target other endocrine glands such as the thyroid, liver, pancreas, adrenals or testes/ovaries. Other endocrine glands include the pineal gland, parathyroid gland and thymus gland.

Whilst the pituitary gland makes its own hormones, it is still only carrying out the instructions it receives from the hypothalamus. The ‘third layer’ and frontline gland in this system would be any one of the glands that act on cues from the pituitary; these are the glands that release hormones that moderate the function of the body and its cells. An example of a daily homeostatic response is balancing sex hormones.  

Beyond simply controlling libido and sexual function, hormones like oestrogen and testosterone cause powerful interactions in the striatal cortex of the brain, the area that determines mood, energy, personality – essentially, almost everything that makes us the person we are. In a man, the HPTA (hypothalamic pituitary testicular axis) is the key to maintaining balance of such an important system. The hypothalamus senses how much SHBG (sex-hormone binding globulin) and free serum testosterone there is in circulating blood and, should it drop to sub-optimal levels,

With such an intricate system constantly at play, there can be times where homeostasis is disrupted. Where this happens, the only excess/deficiency felt by the individual would be the frontline hormones (eg. testosterone) that directly acts on tissue; however, an individual will not feel a deficiency of LH or GnRH. Because both of these can be affected by dietary deficiencies, fatigue and stress (as well as gland dysfunction), a number of factors must be considered before an attempt to re-establish a beneficial state of homeostasis is attempted. Too often, doctors dabble with the frontline hormones without dealing with the core problems upstream, leaving the patient at the mercy of a damaging imbalance of powerful hormones. This one-dimensional folly can be seen in action in the field of testosterone replacement.

The hypothalamic-pituitary axis is involved in all hormonal production and balancing so, naturally, this includes hormonal fluctuations triggered during the stress response. Whilst stress responses are controlled through the same mechanisms, they do not work purely through the same ‘layered’ loop system for constant feedback. Whilst there is a stress-induced increase in hormone production through the hypothalamic-pituitary axis (which affects all other endocrine glands ‘downstream’), there is also a significant part played by the central nervous system. When the body reacts to stressors, the hypothalamus sends nervous impulses to the sympathetic centres in the spinal cord (the sympathetic nervous system, sometimes referred to as SNS, is the reactive part of the nervous system.

Following a stressful reaction, the parasympathetic nervous system, or PNS, ‘calms’ the body to counter the changes). These sympathetic centres stimulate the splanchnic nerves and the adrenal medulla, which increases production of epinephrine (eg. adrenaline) and norepinephrine. These chemicals are anti-inflammatory and help the body deal with stress through a number of methods; increase in heart rate and blood pressure, vasodilation of blood vessels around the body, increased sweating, slowing of digestion, dilation of airways and increase in glycogenolysis. This cascade of changes is often labelled the Fight or Flight response, as the combination of changes prepares the body to engage in combat or flea.

Whilst this is a very complex system that facilitates an effective state to deal with a stressor, this is not the sum of the Stress Response. Simultaneously, the hypothalamus stimulates the pituitary gland to release hormones that can help in a stressful situation. This includes hGH (Human Growth Hormone), which stimulates the liver to increase the level of fatty acids and glucose in the blood, and ACTH (adrenocorticotropic hormone), which increases production of many hormones, especially aldosterone and cortisol, which is itself often labelled the body’s ‘stress hormone’. TSH (thyroid stimulating hormone) is also released, which increases cellular activity and catabolism to help produce more energy to deal with the immediate requirements.

It is these immediate/short-term changes that, whilst required to deal with life-or-death situations, can inadvertently instigate a shift in the activities of the body. This is where homeostasis is disturbed through the Stress response. A homeostatic response is now required in order to return to ‘normality’ (although a stressed individual may not be able to remove themselves from the stressor, ensuring this remains impossible). Herein lies a major difference between homeostatic responses and stress responses; the stress response is turned ‘on’ or ‘off’ in correlation to perception of stress/danger. Homeostatic response is a constant default that, provided all its parts are given the raw materials they require to do their job, corrects imbalances rather than causes them.

Homeostatic responses work by detecting the optimal level of a substance then establishing this balance, maintaining it long-term. There will always be levels at which there is too much or too little of a substance, and the job of the hypothalamus is to ensure that the level remains between that and so only needs to act when the readings are outside of these parameters. This ensures long-term health.

Stress responses, however, work in the opposite way. Generally, they will affect a chemical that has been previously stabilised by the hypothalamus, increasing/decreasing it to levels otherwise considered unbeneficial. This extreme changes are to allow the body to deal with extreme changes and stress response is generally a short-term mechanism and is designed as such; repeated exposure to stress causes major imbalance. Otherwise, stress response ensures short-term survival.

However, over the course of a typical 24 hours, the stress response and the homeostatic response will work with one another to best change the physiological conditions of the body to best match the environmental conditions around it. Different situations demand different characteristics from the body, and that is where these two different systems work together so well in alternating their dominance.

Although they control hormonal fluctuations in different ways, the basic difference is that homestatic responses aim to neutralise and normalise, where stress shifts hormone/chemical levels to abnormal limits to counter the otherwise damaging effects of a stressor, such as organ damage. They are a good example of apparently opposing yet complementary systems.

Although their relative effects are often opposite to one another, I consider them to be very linked in function, so much so that I would class them as similar. Both systems have abilities of detection, multi-layered methods of expression and, most importantly, the constant aim of providing the right chemical balance to the right tissues all of the time, regardless of the situation.

Evolution has dictated that these systems, in unison, represent the best combination of short-term and long-term health management to deal with our natural environment; these two systems share are similar in that the chemical and hormonal fluctuations that they instigate are intrinsic to our daily lives, but also co-dependant should we wish to emerge from real life with both our lives and health intact.