A resting adult is seated in a room at 21°C wearing light clothing. Under these thermoneutral conditions, which mechanism accounts for the GREATEST proportion of total body heat loss?

• A Evaporation from skin and respiratory tract
• B Conduction to surrounding objects
• C Radiation from the body surface ✓
• D Convection by air currents

Explanation

At ambient temperatures below skin temperature (around 21°B in light clothing), radiation accounts for approximately 40% of total heat loss, making it the largest single mechanism. Evaporation contributes about 25% under resting thermoneutral conditions. Conduction and convection together account for most of the remainder. As ambient temperature rises toward skin temperature, evaporation becomes the dominant pathway.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.