Living beings, both animals and plants, are open systems that obtain nutrients and gases from the environment and excrete waste substances in our environment on a continuous basis. What for us are feces, for other microorganisms and invertebrates are succulent substances that become part of their tissues (organic matter), thus allowing the continuation of the carbon cycle within the trophic chains of ecosystems.
Being an open system is necessary for survival: energy is not created or destroyed, it is only transformed (according to the law of conservation of energy) and, therefore, we must obtain it from the environment continuously. In any case, this also has several negative points, such as that we constantly dissipate heat in the environment, we depend on our environment for all our biological tasks and we can get sick and die as a direct consequence of what happens in our environment.
To put some order in the changing chaos that is the environment, our bodies present a series of biological and / or physiological regulation mechanisms to maintain a stable internal condition, compensating for the changes that may occur in the environment. Let’s see how they are.
What is a regulatory mechanism?
In biology, a mechanism is a system with parts that interact causally, giving rise to processes that have one or more effects on the environment, be it internal, external or both . A mechanism may be the process that leads to the sweat of the human being in a hot moment (physiology), but natural selection or genetic drift are also considered mechanisms, although in this case of an evolutionary nature.
In the world of regulatory mechanisms, nothing is black or white, since biological entities are extremely complex beings (multicomponential), whose systems are in continuous interaction and feedback . Beyond its diversity, three great levels can be distinguished in the underlying mechanisms of a living being:
- Genetic mechanisms: lowest in the hierarchy. The functioning of genes and their expression is essential, but they correspond to the basal substrate of any system.
- Mechanisms of cellular functioning: the next mechanism is that which concerns the cell, and therefore the organs and tissues of the body.
- Nervous and endocrine mechanisms: they are the most advanced regulatory mechanisms on the evolutionary scale.
All living beings have genetic mechanisms, because by definition, a cell must have a genome to self-replicate on future occasions (even if it is only one chromosome, as in bacteria). On the other hand, every living entity must present at least one cellular regulation mechanism, since the basic unit of life is the cell, although it makes up the entire organism (as is the case with bacteria and archaea).
As you can imagine, the pinnacle of physiological regulation mechanisms (glands and neurons, which are part of the endocrine and nervous systems, respectively) is restricted to the most evolutionarily complex animals , such as vertebrates, although other living beings also have its own nervous and endocrine scales.
At this point, it should be noted that regulatory circuits can present two feedback systems (feedbacks): positive and negative. We explain what they consist of in a brief way in the following lines.
1. Negative feedback
On this occasion, the regulation mechanism seeks to keep a parameter X under control in a very specific spectrum, always close to the value X0 , which is the maximum optimum in a specific environment. The values of the X parameter are collected from the environment or internal environment through information channels (such as thermoreceptors and other nervous groups) and the information is brought to the center of the mechanism, which will generate responses based on the environment in the best possible way.
2. Positive feedback
In this case, things change. The objective of the positive feedback regulation mechanisms is to reach the maximum point of effectiveness of the parameter X, deviated from the value X0, once certain conditions have been reached .
Although we move around quite complex concepts, the difference between negative and positive feedback is very easy to understand: in the first case, the system responds in a direction opposite to the signal, that is, it tends to “stabilize” the output. of the system so that it remains in constant condition. On the other hand, in positive feedback the effects or outputs of a system cause cumulative effects at the input. In the latter case, it is a system that, by definition, presents an unstable equilibrium point.
Examples of regulatory mechanisms
We have moved between quite ethereal concepts, so it will be useful to exemplify a little what a regulatory mechanism is from a physiological point of view. Let’s say, for example, that we want to understand how sweating occurs in humans. Go for it.
First of all, it should be noted that sweating is a regulatory mechanism modulated by the sympathetic nervous system, which is responsible for many involuntary functions in humans . Our hypothalamus contains neurons in the anterior and preoptic area specialized in recording changes in internal temperature and in the activity of the cerebral cortex. Therefore, when the information arrives that there is an excess of heat (be it internal or external), the hypothalamus sends the signal through cholinergic fibers to the eccrine glands distributed throughout the skin so that they excrete sweat.
Sweat comes out through the pores that connect the eccrine glands with the skin. Since fluids need heat to evaporate (after all, heat is energy), they “catch” this excess temperature from the body’s surface, which causes our general system to cool down. Through the evaporation of sweat, 27% of body heat is dissipated, so it is not surprising that this mechanism is activated by any physical and / or environmental variation .
In this case, we are at a theoretical level before a negative feedback regulation mechanism. The organism’s interest is to maintain body temperature (parameter X) in a suitable range as close as possible to the ideal, which is between 36 and 37 degrees. In this system, the functional complex responds inversely to external stimuli.
If we get philosophical, we can also conceive of natural selection itself or genetic drift as regulatory mechanisms from an evolutionary point of view. Natural selection exerts pressure on the open system that is a population, selecting the genes that are most beneficial in the long term and disregarding the least adaptive ones.
For example, an animal of a bird species that is born (by a de novo mutation) with a larger beak than the rest, could have a greater facility to hunt insects among the bark of trees. As this living being has an advantage over the rest, it will be able to feed more, it will grow more and, therefore, it will be stronger when it comes to competing with the rest of the males to reproduce. If the “big beak” trait is heritable, it is to be expected that the offspring of that animal will be more viable than the rest.
Thus, over the generations, the “big peak” trait would increase in the population, since simply those that present it live longer and have more opportunities to reproduce. Natural selection acts as a clear evolutionary regulation mechanism in this case, since the proportion of genes in a population varies according to the impositions of the environment.
As you may have seen, regulatory mechanisms in the world of biology go far beyond thermoregulation or energy consumption. From the expression of genes to the evolution of species, everything can be summarized in a positive or negative feedback that seeks to reach a maximum point of effectiveness , at one point or another. In the end, the goal is to achieve the maximum internal balance in every possible way, always taking into account environmental constraints.
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