28.19 : Body Temperature

Body temperature reflects the equilibrium between heat production and heat loss within the body. Most heat is generated by metabolically active tissues, particularly the liver, heart, brain, kidneys, and endocrine organs. At rest, skeletal muscles contribute 20–30% of total heat production, but during vigorous exercise, this can increase up to 30–40 times.

The average body temperature is approximately 37°C (98.6°F) and typically ranges from 36.1–37.2°C (97–99°F), remaining relatively stable regardless of external conditions. Body temperature exhibits slight daily fluctuations, with the lowest levels occurring in the early morning and the highest in the late afternoon or early evening. Increased temperatures accelerate enzymatic activity, with a 1°C rise enhancing chemical reaction rates by about 10%. However, temperatures above the normal range can lead to neuronal depression and protein denaturation.

Different body regions maintain varying temperatures at rest, with the core (organs in the skull, thoracic cavity, and abdominal cavity) being the warmest and the skin, or shell, the coolest. Core temperature is tightly regulated, with blood as the primary medium for heat exchange between the core and shell.

The preoptic area of the hypothalamus, located in its anterior region, acts as the body's thermostat. This area receives input from thermoreceptors in the skin and hypothalamus, monitoring blood temperature. Based on this input, it modulates the frequency of action potentials, triggering responses in other parts of the hypothalamus to either lower or raise body temperature as needed.