Skin Thermoregulation: Vascular & Sudomotor Mechanisms

Vascular Control (Sympathetic Adrenergic)

• Heat: Active vasodilation (cholinergic co-transmission) + withdrawal of vasoconstrictor tone → ↑ skin blood flow (up to 6–8 L/min) → radiant/convective heat loss
• Cold: Intense vasoconstriction (α-adrenergic) → ↓ skin flow (<0.1 L/min) → countercurrent heat conservation

Sudomotor Control (Sympathetic Cholinergic)

• Heat: Acetylcholine → muscarinic receptors on eccrine glands → sweat secretion → evaporative cooling (major in humans)
• Non-thermoregulatory sweating: Emotional (palms, axillae), gustatory

Integration

Preoptic anterior hypothalamus (POAH) → thermoregulatory centers → sympathetic outflow. Cutaneous thermoreceptors provide afferent input.

Clinical Correlates

• Anhidrosis → heat stroke risk
• Autonomic failure (diabetes, Parkinson's, pure autonomic failure) → impaired vasodilation/sweating
• Raynaud's: exaggerated digital vasoconstriction