The Methods Of Homeostatic Regulation
Living beings are continuously exposed to a multitude of stimuli. Therefore, it is necessary to have homeostatic regulation mechanisms capable of maintaining internal stability.
Homeostasis and internal environment
In the middle of the 19th century, the French physiologist Claude Bernard realized the constancy of the internal environment in which the cells of organisms were arranged, in the face of the changing properties of the exterior.
Almost a century later, the American physiologist WB Cannon established that this equilibrium was the result of a set of physiological mechanisms capable of maintaining a series of concentrations or internal values necessary for survival.
Canon proposed the term homeostasis to refer to the ‘stable’ character of the internal environment, as opposed to external fluctuation. Paradoxically, the complexity of these physiological processes lies in a constant self-regulatory dynamics.
Mechanisms of homeostatic regulation
The cells of living beings only maintain their viability within specific ranges of temperatures, pH, ionic concentrations and nutrients according to the species. However, organisms depend on a changing external environment to obtain the matter and energy necessary for internal balance.
The mechanisms of homeostatic regulation can be classified into:
- Negative feedback : it occurs when the value of a variable is higher or lower than that required for the functioning of a certain process or physiological mechanism. In response, a regulatory mechanism is activated to inhibit the synthesis of said variable or reduce its potency.
The regulation of blood glucose levels or the maintenance of body temperature are some of the biological processes regulated in this way.
- Positive feedback : less frequent than the previous mechanism, it contributes to the increase of a process or function.
It occurs in the initial stages of the action potential, when a small depolarization of the plasma cell membrane generates the opening of sodium channels that, upon entering the intracellular space, induce the opening of more sodium channels. In this way, a greater cellular depolarization is achieved. There would also be a positive regulation in the early stages of ovulation.
- Antefeeding : a mechanism that allows an organism to anticipate highly probable events. It can be both negative and positive in nature and they mainly stand out in metabolic chains and neuronal communication and coordination processes.
The increase in heart rate in the moments before an imminent physical effort or even the functioning of the cerebellum itself, which, anticipating the state of the neuromuscular system once movement begins, can execute the necessary nervous orders.
Homeostasis and allostasis
Once the homeostatic theory with which Bernard and Cannon justified the stability and functioning of the internal environment had been exposed, in 1988 the neuroscientist Sterling proposed an opposite view, or, as later discovered, complementary to homeostatic regulation: allostasis.
Allostasis is a regulatory mechanism that, unlike homeostatic equilibrium, proposes that organisms to cope with disturbances from the external environment alter the constancy of the internal environment. An example occurs with blood pressure, which fluctuates between higher or lower values depending on a specific external state and, if kept constant, would cause the death of the individual.
This idea eventually led McEwen to propose allostasis as the process that actively maintains homeostasis. That is, it maintained the stability of the internal environment through change.
