Body Temperature

The average human body temperature is approximately 37°C (98.6°F), typically ranging from 36.1–37.2°C (97–99°F). Body temperature remains relatively stable regardless of external conditions due to the balance between heat production and heat loss. Slight daily fluctuations occur, with the lowest temperatures in early morning and highest in late afternoon or evening.

Metabolically active tissues generate most body heat, 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. These organs maintain continuous metabolic activity that sustains core temperature.

Blood serves as the primary medium for heat exchange between the core and shell. When the shell is warmer than surroundings, heat is released as blood flows into skin capillaries. Conversely, when heat must be preserved, blood mostly bypasses the skin. This dynamic adjustment maintains thermal equilibrium with the external environment.

The core, containing organs in the skull, thoracic cavity, and abdominal cavity, maintains the highest temperature. The skin or shell remains the coolest region. This temperature gradient reflects the core's metabolic activity and the shell's direct exposure to the external environment, creating a natural thermal hierarchy.

Elevated core temperatures accelerate enzymatic activity, with each 1°C rise enhancing chemical reaction rates by approximately 10%. However, temperatures significantly above normal can denature proteins and depress neuronal activity, impairing critical physiological functions and potentially causing homeostatic imbalances in body temperature.

The preoptic area of the hypothalamus acts as the body's thermostat, receiving input from thermoreceptors in the skin and hypothalamus that monitor blood temperature. Based on this sensory information, it modulates the frequency of action potentials, triggering responses in other hypothalamic regions to either lower or raise body temperature as needed.

Low core temperature can result in cardiac malfunction and impaired physiological processes. Fluctuations in core temperature are hazardous because the body's regulatory systems depend on precise thermal conditions. Maintaining stable core temperature is essential for proper neuronal function and cardiovascular performance.