Maintaining homeostasis by prophecy

Homeostasis is the idea of an ideal internal milieu for the cells that the body strives to maintain. The idea was initially proposed by Walter B. Cannon and remains a central tenet of physiology. One of the most basic regulatory mechanisms used to achieve this is negative feedback, wherein a change in some important parameter triggers a compensatory response that serves to bring it back toward the optimal level. This entails that for any true homeostatic parameter there should be an ideal set point. However, there are many such systems that will reset the regulation of their parameter either in response to outside stress, or in disease. Many, if not most researchers have had no problem with expanding the remit of homeostatic regulation to include resetting and learnt neurohormonal mechanisms that might anticipate an environmental challenge. But others felt the need to come up with new words to encapsulate these parts of physiological regulation.

One attempt to conceptualise this is the idea of allostasis, or achieving stability through change. Either change in the set point of a parameter, or change in behaviour, and that this could even be done in anticipation of a change in environment. This is different from the classical view of homeostasis where the organism reacts to a change in a critical parameter and strives to return it to normal. However, allostasis is still poorly defined and researchers that use the term do not agree completely what it means. Some see it as an extension of normal homeostatic physiology, others see allostasis as a pathological process. When you see it as pathological it makes sense to talk about the extra energy expended to change and maintain a homeostatic set point at a new level, or the extra energy expended to perform a changed behaviour. To describe this the researchers who see allostasis as pathological use the term allostatic load, or allostatic stress.

Anyway, if we return to the perspective of the cells with a speculative example; A kidney cell cannot sense a change in outside temperature that will lead to increased metabolic rate, that will lead to increased protein intake, that will lead to increased urea production, that will require increased glomerular filtration in the kidney. So, it has developed a brain and a skin with temperature sensors that tells the brain that it is colder out isde. The brain can then tell cells that produce heat to produce more heat to maintain body temperature. The brain can potentially also tell the kidney that it is making the heating cells work harder and thus that glomerular filtration will need to increase in the near future. While, this example is mostly speculation it serves as an example of a mechanism that would be difficult to fit into a classical homeostatic mechanism. Thereby, it illustrates the usefulness of a new concept whereby a kidney cell could develop a prophetic (for other kidney cells) ability to foresee the need increased work in the future.