Longevity, Magazine

6. homeostatic resilience - Hallmarks of Health

Homeostatic Resilience Article image Hallmarksofhealth

Summers are getting hotter and hotter and weather conditions are becoming increasingly extreme. All living things try to cope with these strong fluctuations while keeping their own systems constant. Our body is no exception: at increased temperatures, our own body temperature ideally does not rise, but we sweat so that the excess heat leaves our organism again. However, cooling down by sweating also means work for the body and thus increased energy consumption. The heart rate increases and the energy needed for cooling down has to be supplied quickly - but is also lacking in other places at the same time. For this reason, we feel tired, get tired more quickly and can't do sports as efficiently.

There are some physiological functions that are always kept in balance for our body to function. This balance is called homeostasis. The body's ability to keep this balance constant even under extreme conditions - such as heat in this example - is then called homeostatic resilience.

The term resilience is more familiar from psychology and describes the stress resistance or resilience to deal with difficult situations. Physiological parameters that are kept in balance are, for example, blood pressure, arterial oxygen capacity, heart rate, body temperature, hormone levels, pH or body temperature. These values cannot be kept completely static, but fluctuate "homeodynamically" within a buffer capacity. The greater the buffer capacity, the higher the resilience of the system.

Balance equilibrium

Neuronal Mechanisms - Homeostatic Resilience in the Brain

As the central switching mechanism of the body, the brain with its neuronal circuits is also the first port of call for homeostatic regulation. In order to react to external influences and to adjust and balance the inner equilibrium, our body works a lot with hormones. The release of hormones is mostly controlled by commands from the brain. The main control over it lies in the hypothalamus and the spinal cord. Here begin two central axes of the nervous system that regulate the production and release of hormones.

The faster axis activates, starting from the spinal cord, the release of hormones in the adrenal medulla. It is part of the sympathetic nervous system and is called the sympathetic-adrenal medullary axis (HNA). Adrenaline and noradrenaline are produced in the adrenal medulla. The second axis(HPA) activates the release of glucocorticoids in the adrenal cortex. The control for this is located in the hypothalamus, which triggers the pituitary gland (hypophysis) to release adrenocorticotropic hormone (ACTH). This hormone then finally activates the release of glucocorticoids in the adrenal medulla. Due to these intermediate steps, the system is significantly slower.

" Here you can read more about the glucocorticoid hormone cortisol.

The release of stress hormones serves as a protective mechanism for the body. However, a stress reaction that is too long and/or too high can have a harmful effect on the body. "Peeing your pants in fear" is therefore not sensible from a medical point of view.

Metabolism - anabolism and catabolism

Besides neuronal mechanisms, metabolic cycles are also involved in the balance, which is co-controlled by hormones. As you may know, metabolism refers to metabolism and can be divided into anabolism and catabolism. Anabolism you know most likely from the term anabolic steroids. These promote muscle building and are popularly, but forbiddenly, used in bodybuilding sports. Anabolic processes build up the body's own substances and usually consume energy in the process. The counterpart to this is the catabolic metabolism. Here, endogenous substances are broken down while energy is released. A very simple example of these two opposing metabolisms is the storage of body fat (anabolic) and the breakdown of body fat (catabolic).

Fat as an underestimated commodity

In our society, fat - whether as a food component or as a bulge on the body - usually has a negative connotation. Wrongly so. Fat can do a lot. Among other things, it can supply and store a lot of energy. One gram of fat can store and supply more than twice as much energy as the same amount of carbohydrates. It is the most efficient source of energy. Therefore, the body stores most of the excess energy in fat, so to speak, to create reserves for worse times and not to waste energy - this is anabolism.

However, here too - as with everything - the dose makes the poison. Because too much body fat and too much fatty food massively increase the risk of cardiovascular disease and other illnesses. However, it is important to know that a high body fat percentage does not automatically indicate the person's lifestyle. Some diseases promote fat storage and those affected suffer both the physical and psychological consequences through stigma. The breakdown of body fat occurs when the body acutely has no other energy sources available. Then the energy of the body fat is used - this is called catabolism.

Back to homeostasis: A good balance between anabolism and catabolism and good resilience to major fluctuations tends to indicate good health and consequently increased longevity. A constant and excessive alternation between anabolic and catabolic processes would stress the body.

Fast Food Burger Unhealthy
Fast food has an unfavorable nutritional composition, which makes it conducive to a higher body fat percentage.

Immune System and Homeostatic Resilience

Repeated outbreaks of disease show us again and again: a good immune system is a mainstay of our health. When an infection hits our body, the innate and acquired immune systems have some tools at hand to deal with it. It is not good if the immune system overreacts to a harmless infection, starting too high a fever and inflammation, thereby damaging itself. Nor is it good if the immune system does not react at all and thus the infection can simply spread.

As you learned in the Hallmark of health article on circuitry, almost all functions of the body are interconnected and interdependent in certain ways. For example, elevated levels of cytokines (immune system messengers that activate inflammation and immune responses) cause activation of the HPA axis. As a reminder, glucocorticoids such as cortisol are released via the HPA axis.

At the same time, however, they also influence the receptors at which glucocorticoids act. The receptors can then no longer transmit the effect of the glucocorticoids so well and the actual reaction occurs only to a reduced extent. A kind of glucocorticoid resistance develops, since the glucocorticoids are secreted but no longer have any effect. One function of glucocorticoids is normally to downregulate cytokines and thus inhibit the immune system. However, when such a loop occurs, the cytokines can no longer be down-regulated and a vicious circle begins - homeostatic resilience is lowered.

Microbiome

It is now widely recognized that the gut and the microbiome are important cornerstones of health. After all, the intestinal barrier influences what of our food actually ends up in the bloodstream and thus becomes biologically active. The interaction is described in expert circles as the microbiome-gut-brain axis. If the flora in our intestines is out of balance, this has an effect on several other bodily functions, such as the immune system or the psyche.

Every person has an individual flora, which can also get out of balance at times. The microbiome can be damaged to a greater or lesser extent, especially by serious illnesses. A resilient microbiome means that even if fluctuations occur, the effects are not so great and the body has the ability to balance these fluctuations well and thus contribute to an overall healthy body. The foundation for this is laid in childhood. Those who have built up a stable and well-functioning microbiome as a child usually cope better with later deviations.

Lake ship homeostasis
Resilient homeostasis has a stabilizing effect on all systems of the human body.

Homeostatic resilience as captain in turbulent seas

In life, the entire body reacts to external and internal fluctuations with adjustments on different levels. You can imagine these cycles like a sailboat on the high seas. External circumstances such as high waves or strong winds can throw the boat off balance and require a good team on the boat to restore balance by taking appropriate action on the sails and shifting weight. However, the boat can also be upset by crew members, sails hoisted incorrectly, or material problems. In any case, readjustment is needed on many levels.

The better and calmer the boat itself is in the water and the better the crew members know the sailing ship and are attuned to each other, the sooner a good equilibrium can be restored from a turbulence. Well-rehearsed and inherently resilient individual components make the entire system safer against threats.

Literature:

López-Otín, Carlos, and Guido Kroemer. "Hallmarks of health." Cell 184.1 (2021): 33-63. https://pubmed.ncbi.nlm.nih.gov/33340459/

Images:

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