Thermoregulation in Human Physiology

Introduction to Thermoregulation

• Overview of thermoregulation in human physiology.
• Importance of maintaining body temperature around 98.6°F (37°C).

Homeothermic Characteristics

• Definition: Homeothermic refers to the ability to maintain a stable internal body temperature despite external fluctuations.
• Body temperature variations based on measurement location (core vs. shell).

Body Temperature Measurement

• Different measurement sites:
  • Oral Temperature: Under the tongue; influenced by food/drink.
  • Axillary Temperature: Under the armpit; stable but cooler than core.
  • Otic Temperature: In the ear; considered shell temperature.
  • Rectal Temperature: Core temperature; most accurate measure of body temperature.
• Core temperature (inside skull, thoracic cavity) usually higher than shell temperature.

Heat Production and Loss

• Balance of heat production, retention, and loss for temperature regulation.
• Metabolically Active Tissues: Brain, heart, liver produce more heat than less active tissues.
• Heat production mechanisms include:
  • Chemical thermogenesis (epinephrine, norepinephrine raise metabolic rate).
  • Shivering: Involuntary muscle contractions generating heat.
  • Thyroxine Influence: Increases metabolic rate over longer periods.

Mechanisms of Heat Loss

• Predominantly via Radiation: About 60% heat lost through infrared waves (thermal energy).
• Other methods:
  • Conduction: Direct transfer of heat through contact (e.g., sitting on a cold chair).
  • Convection: Loss of heat aided by moving air or water (e.g., fans to cool off).
  • Evaporation: Loss of heat as sweat evaporates; accounts for ~25% of heat loss.