Thermoregulation in the Human Body
Core Concept
Thermoregulation is the body's process of maintaining a stable core temperature around 37°C (98.6°F), which is essential for normal cellular function and survival. 1, 2
How the Body Maintains Temperature
The body uses a coordinated set of automatic (autonomic) responses to balance heat production and heat loss 3:
Heat Detection System
- Peripheral sensors in the skin detect external temperature changes 1
- Central sensors in the brain and spinal cord monitor core body temperature 1
- These sensors communicate through specialized temperature-sensing channels (transient receptor potential channels) 1
Heat Loss Mechanisms (When Too Hot)
Vasodilation: Blood vessels near the skin surface expand, allowing more warm blood to flow to the skin where heat can escape 1, 4
Sweating: The body produces sweat that evaporates from the skin surface, cooling the body through evaporative heat loss 1, 3
Behavioral changes: Seeking shade, removing clothing, or reducing activity level 1
Heat Production Mechanisms (When Too Cold)
Vasoconstriction: Blood vessels near the skin surface narrow, reducing blood flow to the skin to conserve core heat 1, 3
Shivering: Involuntary muscle contractions generate heat, increasing body temperature at a rate up to 3.6°C per hour 5, 1
Non-shivering thermogenesis: Brown adipose tissue (brown fat) generates heat without shivering, particularly important in infants and increasingly recognized in adults 1
Piloerection: "Goosebumps" from hair standing up (more effective in furry animals than humans) 1
The Blood as a Heat Exchanger
The circulatory system acts as the body's primary heat distribution network 4:
- Blood carries heat from the metabolically active core (organs, muscles) to the skin surface 4
- Specialized blood vessels called arteriovenous anastomoses (AVAs) in hairless skin areas (palms, soles, face) can accommodate very high blood flow rates for efficient heat exchange 4
- This forced convection system enables rapid temperature adjustments based on environmental conditions 4
Clinical Significance
The thermoregulatory system can be overwhelmed by extreme environmental conditions or excessive physical exertion, leading to dangerous hypothermia (<35°C) or hyperthermia (>40.5°C) 6, 3:
- Hypothermia causes shivering, confusion, cardiac problems, and can progress to coma 3
- Hyperthermia causes sweating, weakness, confusion, and can progress to life-threatening heat stroke 3
- Children with adequate hydration have similar thermoregulatory capacity as adults, contrary to older beliefs 5, 7
Key Modifiable Risk Factors
When thermoregulation fails during physical activity, it typically reflects preventable issues 7: