Storyboard

Thermoregulation maintains core temperature (T_core) at 36.537.5°C despite enormous variations in metabolic heat production (60 W basal 1500 W peak exercise) and environmental conditions. The hypothalamus functions as a thermostat: it detects T_core through central and peripheral thermoreceptors, and generates efferent responses (cutaneous vasomotricity, sweating, shivering) according to the T_core - T_set error.

The thermal balance of the body (first principle) shows that four dissipation mechanisms compete: convection (proportional to T air-skin and h_c, which varies with the wind), radiation (proportional to T according to Stefan-Boltzmann), evaporation (the most powerful in extreme heat or exercise: up to 1.35 kW with maximum sweating) and conduction (lower contribution except immersion in water).

Vascular heat flow to the skin is the main control mechanism: cutaneous vasodilation increases peripheral blood flow up to 78 L/min (vs. 0.20.5 L/min in cold), reducing R_vascular by 50×. Skin temperature rises, amplifying Q_conv and Q_rad. Vasoconstriction has the opposite effect: in cold, R_vascular increases, the core is thermally isolated from the environment and T_skin can fall to 20°C while maintaining T_core at 37°C.

The two-compartment model (core-skin) allows predicting the temporal dynamics of T_core and T_skin in the face of environmental or activity changes: the time constants _c = m_c·c_c·R_cs (core, ~3060 min) and _s = m_s·c_s·(1/h_c) (skin, ~515 min) determine how quickly the system responds. In the induction of therapeutic hypothermia (target 3336°C post-PCR), the skin is externally cooled; T_core follows with 3060 min delay.

Fever is an increase in T_set (not T_core above the set point): pyrexins (IL-1, IL-6, TNF, PGE) raise T_set in the hypothalamus the body perceives 'cold' even if it is at 37°C shivering, vasoconstriction T_core rises to the new T_set (3840°C). Hyperthermia (heat stroke) is different: T_set is normal but T_core rises due to excessive environmental heat or failure of dissipation mechanisms, without an adequate sweating response.

>Model

ID:('ky', 45)

Description

ID:(0, 45)