Physiological and Pathological Significance of Temperature
In humans and all warm-blooded animals, body temperature is one of the key plastic constants. The essence of this concept is that the organism is permitted to deviate from the optimal temperature level, but strictly for a limited period.
The physiological significance of this parameter is immense: it sets the optimal level of vital activity, which, in turn, is fundamentally determined by tissue metabolism.
Depending on current parameters, three main states are distinguished:
- Normothermia — the optimal temperature at which all metabolic processes occur most efficiently.
- Hypothermia — a drop in body temperature below the physiological norm.
- Hyperthermia — an elevation in temperature values.
From a pathophysiological perspective, prolonged exposure to either hypothermia or hyperthermia leads to significant disruption of normal vital processes.
Homeothermy: Constancy Regardless of the Environment
Homeothermy (from Greek homoios — similar) is the ability of higher animals and humans to maintain body temperature within strict optimal limits, regardless of how cold or hot the external environment is. Organisms with this type of regulation are also called warm-blooded.
An adult successfully adapts to changes in external temperature by balancing two opposing processes:
- Changes in heat production (heat generation in tissues).
- Changes in heat loss (heat dissipation into the environment).
A crucial feature of homeothermy in humans is its gradual maturation during ontogeny. Regulatory mechanisms form only several months after birth. This is precisely why a newborn infant is completely incapable of independently maintaining thermal balance and, without external warming, may perish from cooling.
Poikilothermy and Heterothermy
An evolutionarily more ancient type is poikilothermy (from Greek poikilos — varied). This is the complete inability to maintain a constant body temperature: it depends directly on external conditions. Such animals (cold-blooded) include amphibians and reptiles.
When the environment cools, their temperature drops, and purposeful behavioral activity in the external environment ceases — the animals literally freeze. To survive prolonged cold spells, they enter states of hypobiosis and anabiosis, characterized by a sharp drop in metabolic intensity. As soon as the environment warms up, functions and behavior are fully restored.
The intermediate link is heterothermy (from Greek heteros — variable). This is facultative (inconstant) homeo- and poikilothermy.
- Bats: during active flight, they exhibit homeothermy, whereas during rest (hanging vertically), they transition to a poikilothermic state.
- Hibernators (bears, ground squirrels): become poikilothermic during long hibernation.
Bioligical significance of heterothermy is the total conservation of energy reserves at rest. The primary condition for survival is that the temperature drop must not lead to the freezing of water within the organism. To protect against critical frosts, these animals actively use shelters (burrows, dens, caves).
Evolutionary Aspect of Thermoregulation
The emergence of full homeothermy was a colossal step in the evolution of the animal kingdom. The transition to stable temperature maintenance is inextricably linked with the formation of complex, goal-directed behavior.
The connection here is direct: a stably high body temperature allows for a high metabolic rate. In turn, rapid metabolism ensures fast motor reactions. This exact cascade of changes proved critically important for successful foraging behavior and survival in changing planetary conditions.