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Core body temperature refers to internal temperature, distinguished from skin temperature. Different measurement sites are proxies with their own limitations, not interchangeable readings of a perfectly uniform interior. ^[ref]

Homeostasis is the maintenance of usable internal conditions despite disturbances. It concerns selected regulated physiological variables, rather than keeping every part of an organism unchanged: core body temperature may remain near its usual range while skin temperature, sweating and blood pressure change. Regulation makes a relatively dependable environment for biological cells out of a changing external world. ^[ref]

A useful causal description separates a physiological sensor, a physiological integrator and a physiological effector. The return from the physiological effector's action to the sensed regulated physiological variable closes a feedback control loop. In negative feedback, that return opposes the disturbance. The insulin and glucagon articles already trace the blood glucose example; synaptic integration explains how several inputs can jointly influence a neuron. These are implementations and ingredients, not a requirement that every regulatory loop use one anatomical control center. ^[ref]

Homeostasis is useful precisely because internal activity can change: a nearly steady temperature can conceal a large increase in heat transfer. Conversely, observing a flat trace alone does not identify a regulatory mechanism. The environment might simply be constant, or the measuring instrument too insensitive; a perturbation and an independent response readout provide stronger evidence. The skin-temperature perturbation experiment below makes that distinction tangible.

The historical motivation was the puzzle of stability in changing living material. In his 1932 The Wisdom of the Body, Walter Bradford Cannon emphasized that an organism exchanges material with its surroundings and continually replaces its own structure, yet maintains relatively steady internal conditions. This authored excerpt presents homeostasis as active compensation for external and internal disturbances, rather than a static body. ^[ref]

A physiological set point is a reference around which regulation is organized, analogous to a reference signal. An observed average is not automatically a separately encoded target. A range of acceptable values and different response thresholds can be more informative than a single exact number. Negative feedback describes a causal sign; neither perfect constancy nor complete restoration follows from that sign alone.

For core body temperature, circadian rhythms and fever can change the defended level. Thus a response toward the current physiological set point need not restore yesterday's temperature. A drifting target and imperfect tracking of a fixed target are different explanations for a changing readout. ^[ref]

A regulated physiological variable is a specified internal quantity whose departures elicit actions tending to restore an appropriate range. Examples include core body temperature, blood glucose concentration, blood pressure, and the pH and osmolality of extracellular fluid. Specify the compartment and readout: skin temperature and core body temperature are different quantities, and an insulin concentration is a regulatory message rather than the blood glucose it helps control.

Thermoregulation regulates body temperature. Skin signals can anticipate a change of core body temperature, so a response need not wait for an internal error. ^[ref]

These responses have costs and environmental limits. Shivering consumes metabolic resources; cooling through sweating removes water that must eventually be replaced. High humidity restricts evaporation, so secreted sweat and successful cooling are not interchangeable. Maintaining core body temperature also depends on maintaining circulation: depleted blood volume can compromise skin blood flow and heat transfer. Seeking shade or reducing work changes the disturbance itself, whereas a larger regulatory command merely attempts to counter it. ^[ref]