Skin Thermoregulation: Layers, Mechanisms, and Responses

The skin (≈2 m², largest organ) maintains core temperature (37°C) via structural and physiologic mechanisms:

Layers & Structural Roles

• Epidermis: Keratinized barrier; limits water loss, insulates.
• Dermis: Vascular plexus (thermoregulatory shunting), sweat glands, nerve endings, hair follicles.
• Hypodermis: Adipose tissue — insulation, energy reserve.

Active Mechanisms

• Vasodilation: Heat → cutaneous vessels dilate → radiant/convective heat loss.
• Vasoconstriction: Cold → vessels constrict → conserve core heat.
• Sweating: Eccrine glands secrete → evaporative cooling (major in heat).
• Piloerection: Arrector pili muscles contract → hair stands → traps air (vestigial in humans).
• Shivering: Hypothalamic drive → skeletal muscle oscillations → heat production.
• Non-shivering Thermogenesis: Brown adipose tissue (BAT) activation via sympathetic nerves.

Neural Control

Hypothalamus (preoptic area) integrates core/skin thermoreceptor input → efferent signals via sympathetic (vasomotor, sudomotor, pilomotor) and somatic (shivering) pathways.

Clinical Relevance

• Burns → loss of thermoregulation, fluid loss.
• Spinal cord injury → poikilothermia below lesion.
• Anhidrosis (autonomic neuropathy, drugs) → heat intolerance.