A healthy adult at rest in a room at 22°C with low humidity loses heat primarily by which mechanism?

• A Evaporation of sweat
• B Radiation ✓
• C Conduction to surrounding air
• D Respiratory evaporative loss

Explanation

At rest in a thermoneutral environment around 22-25°C, approximately 60 percent of body heat loss occurs by radiation from the skin surface. Evaporation accounts for only about 22 percent at rest and becomes dominant only during exercise or in hot environments. Conduction accounts for a small fraction. Respiratory losses contribute roughly 2-9 percent at rest. Radiation dominates because the skin is warmer than surrounding surfaces and no active sweating is required.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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