Thermoregulation Physiology: How the Body Maintains Core Temperature

Name: Thermoregulation Physiology: How the Body Maintains Core Temperature
Creator: Cold Tower
Published: 2026-02-27

Category: thermodynamics Updated: 2026-02-27

The preoptic area of the hypothalamus maintains core temperature at 36.5–37.5°C. Skin thermoreceptors (TRPM8 for cold) respond within 100ms. Cold defense mechanisms activate in order: vasoconstriction, shivering, brown fat thermogenesis.

Key Data Points
Measure	Value	Unit	Notes
Normal core temperature range	36.5–37.5	°C	Rectal or tympanic measurement; oral is 0.3–0.5°C lower
Hypothermic threshold	<35	°C core	Clinical hypothermia definition; thermoregulation progressively impaired below this
Thermoreceptor response time	<100	milliseconds	TRPM8 and TRPA1 channels; signal reaches hypothalamus within 200ms
TRPM8 channel activation temperature	8–25	°C	Cold and cool detection; menthol activates same receptor
TRPA1 channel activation temperature	<17	°C	Noxious cold detection; also responds to irritants
Thermoneutral zone (ambient)	20–27	°C	No active thermoregulation needed; minimal metabolic cost for temperature maintenance
Skin blood flow range	0.2–8	L/min	At cold vs. heat; demonstrates vast range of thermoregulatory vascular control

Thermoregulation is the physiological process by which the body maintains a stable internal temperature despite external cold or heat. In humans, the system is highly precise: core temperature is maintained within ±0.5°C of the setpoint even during extreme cold exposure.

The Hypothalamic Thermostat

The preoptic area (POA) of the anterior hypothalamus is the master thermoregulatory center. It:

Integrates thermal signals from skin, spinal cord, and internal organs
Compares integrated temperature to the setpoint (~37°C)
Activates appropriate effectors (vasoconstriction, shivering, sweating)

Two neuron populations in the POA govern the cold response:

Neuron Type	Temperature Response	Effect When Activated
Warm-sensitive (WSN)	Fire rapidly when warm	Inhibit cold-defense (vasoconstriction, shivering)
Cold-sensitive (CSN)	Fire rapidly when cold	Activate cold-defense mechanisms

When core or skin temperature drops, WSN firing rate decreases → disinhibition of shivering and vasoconstriction centers in the posterior hypothalamus and brainstem.

Peripheral Thermoreceptors

Skin contains two molecular classes of cold receptors:

Receptor	Channel	Temp Range	Function
Cool/cold	TRPM8	8–25°C	Innocuous cold; “cool” sensation
Noxious cold	TRPA1	<17°C	Painful cold; irritant response
Warm	TRPV3, TRPV4	32–43°C	Heat sensing; not relevant here

Cold information travels via small-diameter Aδ fibers (sharp cold sensation) and C fibers (slow, burning cold) to the spinal cord, then to the hypothalamus and somatosensory cortex.

Cold Defense Response Hierarchy

The body activates cold defenses in a hierarchical, energy-efficient sequence:

Behavioral response (immediate): seek warmth, add clothing, posture changes
Cutaneous vasoconstriction (seconds): reduces heat loss from skin
Increased metabolic rate (non-shivering): BAT, slight muscle tone increase
Shivering (minutes): gross muscle thermogenesis, 2–5× metabolic rate
Hormonal response (minutes–hours): thyroid hormone, NE, cortisol mobilize fuel

Heat Balance Equation

Core temperature depends on the balance between heat production and heat loss:

Heat production: Basal metabolic rate (~80 W at rest) + exercise + shivering Heat loss pathways:

Pathway	Percentage (cold ambient)	Physical Basis
Radiation	40–60%	Infrared emission from skin
Conduction	15–30%	Direct contact with cold surfaces; ×25 in cold water (water = high conductivity)
Convection	10–25%	Air/water movement over skin
Evaporation	<10%	Sweat and respiration

Cold water accelerates heat loss by 25–30× compared to cold air because water’s thermal conductivity is 25× higher than air. This explains why cold water immersion is so much more physiologically challenging than equivalent air temperature.

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Sources

← All cold exposure pages · Dashboard