HOMEOSTASIS: EXAMPLES, MECHANISMS, FUNCTIONS - BIOLOGY - 2025

The homeostasis is defined as the set of phenomena of autoregulation leading to the maintenance of "record" in the chemical composition and physicochemical properties of the internal environment of an organism.

The word homeostasis derives from the Greek "oμoιo", which is read "homos" and which means "similar" or "similar" and from the suffix "στασισ", which is read "stasis", which means "fixed", "permanent" or "stable."

Erythrocyte and hemoglobin homeostasis. commons.wikimedia.org

The term does not refer to an internal balance or equilibrium, but rather to the maintenance of a constant condition, since a state of balance or equilibrium in a living being means death. This constancy is actively maintained by the body, despite the changes that may arise in the external environment.

Background

Claude Bernard (1813-1878) at the end of the 1870s was the first to refer to the constancy of the “milieu intérieur” (from French internal mean), which represents what is now known as extracellular fluid, in which the cells of an organism are submerged and thanks to which they are kept alive.

The study of the constancy of the internal environment defined by Bernard is what we know today as physiology. The word "physiology" comes from the Greek words "physis" (ϕυυsis) and "logo" (λoyo), which mean "nature, way of being, essence or natural condition" and "what is said about something", respectively.

Many years later, around 1933, the American physiologist Walter Cannon was the one who coined the term homeostasis to describe those mechanisms that each living being has to maintain constant the conditions of its extracellular fluid.

Examples of some physiologically relevant homeostatic functions can be maintenance of blood pressure, body temperature, blood glucose concentration, electrolyte levels in blood plasma, etc., which are maintained in a restricted range despite the great differences between the body and the environment.

Homeostasis concept

Homeostasis is the ability of every multicellular living being to maintain certain parameters or constant conditions in its internal environment, no matter how different the environment that surrounds it is and how fluctuating the environmental conditions are.

This so-called "internal environment" corresponds to the extracellular fluid, contained in the interstitial space (between cell and cell of a tissue) and to the intravascular fluid or blood fluid in animals.

Homeostasis is one of the most important concepts in medicine and physiology (of animals and plants) since all living organisms need their bodies to function within a very narrow range of conditions, namely: pH, temperature, concentration of ions, amount of water, concentration of nutrients, among others.

Some authors consider that “all vital mechanisms, no matter how varied, have the sole objective of preserving the constant conditions of life in the internal environment”, which is why homeostasis defines practically all the internal functions of a being alive.

The preservation or maintenance of internal conditions is possible thanks to a control system that works by negative or positive feedback (to a lesser extent).

This system allows that, when important changes occur in any of the aforementioned parameters, these changes are quickly "neutralized", bringing the body back to its normal condition.

Thus, homeostasis consists of the body's response systems to cope with environmental conditions and the changes to which an organism is permanently subjected.

Homeostatic mechanisms

Homeostasis is achieved thanks to the extensive integration between many of the body systems of an organism.

Cannon (1929) classifies homeostatic mechanisms depending on what is regulated, that is, on "ammunition" or "supplies" obtained from the external environment or from intrinsic "processes".

Blood glucose homeostasis (Source: Christinelmiller via Wikimedia Commons)

Homeostasis by regulation of "ammunition" or "supplies"

The mechanisms of homeostasis by regulation of supplies are characterized by:

- Storage in terms of adjustments between moments of abundance or famine and need.

- Overflow or discharge out of the body when there are "intolerable excesses"

Storage can be of two types, one temporary and the other through segregation. Temporary storage, known as "flood or overflow storage", occurs by "flooding" of interstitial tissues with materials that have been ingested in abundance.

Storage by "segregation", on the other hand, which has to do with the inclusion of the ingested material inside the cells or relatively "permanent" structures.

Therefore, supply regulation homeostasis implies the storage of supplies when there is abundance, in order to increase the reserves to face times of shortage, or the elimination of excesses, when these are toxic.

Homeostasis by process regulation

Although most of the homeostatic regulation depends on the use of external materials or "supplies", there are others that depend much more evidently on the alteration of continuous intrinsic processes, The main examples of this type of regulation are the maintenance of neutrality and the maintenance of temperature in homeothermic animals (capable of regulating their body temperature internally).

Postulates of homeostatic regulation

Cannon, in 1925, proposed six tentative postulates to describe the physiological factors responsible for the maintenance of the internal "constancy" in the body of a living being:

1- In an open system such as the body of an animal, which is composed of unstable materials and which are permanently subjected to variable conditions, "constancy" or homeostasis is direct evidence that there are systems working or ready to function to maintain said constancy.

2- If an organism or a body system maintains homeostasis, it is only because any tendency towards "change" is automatically "neutralized" by an increase in the effectiveness of one or more factors that resist change.

3- Any factor that operates to maintain homeostasis by action in one direction cannot act simultaneously in the opposite direction.

4- Homeostatic agents that are antagonists in one region of the body, can cooperate or work together in another region.

5- The regulatory system that determines a homeostatic state can be made up of a large number of factors that are “activated” at the same time or one after the other (successively).

6- When a factor is known that can change the homeostatic state in one direction, it is reasonable to seek an automatic control for that factor or for factors that have the opposite effect.

Functions of homeostasis

The main function of homeostasis or homeostatic mechanisms is to maintain an internal “balance” in the body of living organisms, especially with regard to parameters such as temperature (homeothermic animals), the concentration of ions and water, the intake of nutrients, etc.

Maintaining "constant" internal conditions within a fairly narrow range and often considerably different from the conditions of the external environment or environment, is essential for the functioning of body systems and, therefore, for life in itself, which is why homeostasis is essential for all multicellular living beings.

Psychological homeostasis

Psychological homeostasis is a term that refers to the psychological or behavioral mechanisms that human beings have to balance the “feelings” of need and satisfaction, in order to maintain what each individual recognizes or perceives as a “normal condition”.

Although the mechanisms of control or regulation of psychological homeostasis differ considerably from those that characterize physiological homeostasis, both processes are closely related.

Psychological homeostatic mechanisms have to do, many times with self-preservation, development and reproduction, adaptation, etc., to name a few.

Examples of homeostasis in the human body

Some of the examples of homeostasis are the maintenance of internal body temperature in humans, the maintenance of glucose levels, the regulation of blood pressure, or the operation of a thermostat.

- Homeostasis in humans

1- Internal body temperature

The internal body temperature of humans is a great example of homeostasis. When an individual is healthy, their body temperature remains at 37º. The body can control the temperature by making or releasing heat.

2- Maintenance of glucose levels

Glucose is a type of sugar found in the bloodstream, but the body must maintain adequate levels of glucose to ensure that a person remains healthy.

When glucose levels get too high, the pancreas releases a hormone known as insulin. If these levels fall too low, the liver converts the glycogen in the blood into glucose again, raising the levels.

3- Functions of the lymphatic system

When bacteria or viruses that can make you sick enter your body, the lymphatic system fights back to help maintain homeostasis, working to fight infection and making sure you stay healthy.

4- Regulation of blood pressure

Maintaining healthy blood pressure is an example of homeostasis. The heart can detect changes in blood pressure, causing it to send signals to the brain, which then sends signals that tell the heart how to respond.

If the blood pressure is too high, naturally the heart must slow down; whereas if it is too low, the heart will have to race.

5- Balance of acids and bases

The human body contains chemicals known as acids and bases, and a proper balance of these is necessary for the body to function optimally. The lungs and kidneys are two of the organ systems that regulate acids and bases within the body.

6- Water level

More than half of the percentage of human body weight is water, and maintaining the correct balance of water is an example of homeostasis. Cells that contain too much water swell and can even burst.

Cells with too little water can end up shrinking. Your body maintains an adequate water balance so that none of these situations occur.

7- Calcium control

The regulation of calcium levels by the human body is an example of homeostasis. When levels drop, the parathyroid releases hormones. If calcium levels become too high, the thyroid helps fix calcium in the bones and lowers blood calcium levels.

8- Physical exercise

Exercise causes the body to maintain homeostasis by sending lactate to the muscles for energy.

Over time, this also signals the brain that it is time to stop exercising, so the muscles can get the oxygen they need.

9- Nervous system and respiration

The nervous system helps maintain homeostasis in breathing patterns. Because breathing is involuntary, the nervous system ensures that the body receives the necessary oxygen when breathing.

10- urinary system

When toxins enter your blood, they disrupt your body's homeostasis. The human body, however, responds by getting rid of these toxins through the use of the urinary system.

An individual simply urinates toxins and other nasty things from the blood, restoring homeostasis to the human body.

11- Rising of the skin

When you suffer that feeling of "goose bumps" it is due to a process of homeostasis that serves to reduce the amount of heat radiated by the skin. It was a very typical process in the skin of our primitive ancestors, but it has been maintained despite the loss of hair in most of the body.

12- Shaking or shivering

When we shiver due to the cold it is because the brain sends signals for the muscles to tell us that the temperature level is below that recommended for our health. That is, the trembling of the muscle is a way to counteract the cold.

13- Vasodilation and vasoconstriction

Vasodilation is the widening of the blood capillaries to cool the blood and fight excess heat. Vasoconstriction is the opposite, being the narrowing of the capillaries so that, in cold environments, blood heat can be conserved.

- Technological homeostatic mechanisms and others

11- Thermostat

Thermostats that work by turning heaters or air conditioners on and off in response to the output of a temperature sensor.

12- Speed ​​regulator

Vehicle cruising that adjusts a car's throttle in response to changes in speed.

13- Autopilot

An autopilot that operates the directional controls of an aircraft or vessel in response to deviation from the course or from a preset compass heading.

14- Controls in industries

The process control systems in a chemical plant or an oil refinery that maintain fluid levels, pressures, temperature, chemical composition, etc. controlling heaters, pumps and valves.

15- Steam engine regulator

The centrifugal governor of a steam engine that lowers the throttle valve in response to increasing engine speed, or opens the valve if the speed drops below the predetermined speed.

16- Business homeostasis

It refers to the ability of a company to maintain its equilibrium state, counteracting internal and external turbulence by absorbing contextual variety.

- Homeostasis in animals and the environment

For warm-blooded animals such as mammals and birds, homeostasis is a combination of internal processes involving hormones, the endocrine system, and metabolism.

On the other hand, for cold-blooded animals like snakes, which do not have such internal systems, they must rely on their external environment to maintain homeostasis.

17- Hormones

In some populations of small mammals such as mice and rabbits, when their numbers increase for some reason, overcrowding creates increasing stress that damages the thyroid gland (which makes essential hormones) and much of the population simply dies from endocrine damage or hormonal.

18- Thermoregulation

In the environment, when atmospheric levels of carbon dioxide increase, plants are able to grow better and thus remove more carbon dioxide from the atmosphere.

Also, wasps and hornets are found in most environments from tropical rain forests, deserts, subtropical and temperate climates. They are able to survive in so many different conditions because they are able to thermoregulate themselves and their nests.

19- Recycling of water in the jungle

Through a system of homeostasis, tropical forests maintain their ability to recycle water. For example, the Amazon basin is surrounded to the north by the savannas and plains of Venezuela and to the south by the savannas of Brazil.

If moisture from the Atlantic Ocean flowed directly back, the Amazon ecosystem would be only a small fraction of its current size.

In fact, the giant trees of the Amazon rainforest rapidly pump moisture into the sky, so that it falls back onto the jungle as rain, thus preventing significant amounts of water from draining away into the ocean.

20- Corals and carbon dioxide

Coral polyps use carbon dioxide to form their shells. This helps decrease the amount of carbon dioxide in the ocean and is one way the Earth fights pollution and works to restore homeostasis.

With fewer corals, the ocean absorbs less carbon dioxide, leaving more in the atmosphere.

References

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