A physiologist's view of homeostasis

Abstract

Homeostasis is a core concept necessary for understanding the many regulatory mechanisms in physiology. Claude Bernard originally proposed the concept of the constancy of the "milieu interieur," but his discussion was rather abstract. Walter Cannon introduced the term "homeostasis" and expanded Bernard's notion of "constancy" of the internal environment in an explicit and concrete way. In the 1960s, homeostatic regulatory mechanisms in physiology began to be described as discrete processes following the application of engineering control system analysis to physiological systems. Unfortunately, many undergraduate texts continue to highlight abstract aspects of the concept rather than emphasizing a general model that can be specifically and comprehensively applied to all homeostatic mechanisms. As a result, students and instructors alike often fail to develop a clear, concise model with which to think about such systems. In this article, we present a standard model for homeostatic mechanisms to be used at the undergraduate level. We discuss common sources of confusion ("sticky points") that arise from inconsistencies in vocabulary and illustrations found in popular undergraduate texts. Finally, we propose a simplified model and vocabulary set for helping undergraduate students build effective mental models of homeostatic regulation in physiological systems.

Population data provide evidence against the presence of a set point for hemoglobin levels or tissue oxygen delivery

“…Our work does aid physiological research as it explains the difficulties finding the physiological substrates of set points (Modell et al. ). It enables clearer explanations as to why hemoglobin levels tend to differ between sexes and races.…”

Allostatic Self-efficacy: A Metacognitive Theory of Dyshomeostasis-Induced Fatigue and Depression

“…As a corollary, the selectionist pressures which act upon the brain during evolution cannot be uncoupled from those acting upon the body's milieu intérieur (Claude Bernard); i.e., control of bodily homeostasis must constitute a primary purpose of brain function (Cannon, 1929). This control has long been known to involve reflex-like actions (comprising motor, endocrine, immunological, and autonomic processes) that are driven by feedback and the resulting “prediction error”—the discrepancy between an expected bodily state (a homeostatic setpoint 2 ) and its actual level as signaled by sensory inputs from the body (Modell et al, 2015); see Figure 4 . Feedback- or error-based reactive control has been studied for many vitally important variables (such as blood acidity, body temperature, blood levels of glucose and calcium, plasma osmolality) (Woods and Wilson, 2013), and the anatomy and physiology of neuronal circuits involved have been mapped out in detail by physiologists over many decades.…”

The effect of exercise on non‐exercise physical activity and sedentary behavior in adults

“…Homeostatic models are characterized by a set point, one or more sensors, and a control center that integrates the signals from the sensor(s), and generates responses targeted at effector organ(s) to maintain the regulated variable within physiologic limits. 58 Before the constrained EE model can be fully accepted, it will be important to identify these components of the homeostatic control system.If TDEE is constrained, what is the ceiling for TDEE in different populations? Does this ceiling change with weight loss or with aging?…”