Body Temperature Regulation: The Hypothalamus & Homeostasis in Action

Homeostasis maintains a stable internal environment (~37°C / 98.6°F). The hypothalamus acts as the body's thermostat.

Thermoregulatory Mechanisms

When Cold (Heat Conservation & Production)

• Vasoconstriction: reduces skin blood flow, conserving core heat.
• Piloerection (goosebumps): traps insulating air layer (vestigial in humans).
• Shivering thermogenesis: rapid muscle contractions generate heat.
• Non-shivering thermogenesis: brown adipose tissue (BAT) activation, especially in infants.
• Behavioral: seeking warmth, curling up.

When Hot (Heat Loss)

• Vasodilation: increases skin blood flow for radiative/convective loss.
• Sweating: evaporative cooling (primary mechanism in heat).
• Behavioral: seeking shade, removing clothing.

Fever vs. Hyperthermia

• Fever: hypothalamic set-point raised by pyrogens (infection/inflammation); regulated.
• Hyperthermia: uncontrolled temperature rise (heat stroke, malignant hyperthermia); set-point normal.

Disorders (hypothalamic damage, thyroid disease, autonomic neuropathy) impair thermoregulation, risking hypo-/hyperthermia.