Homeostasis and Thermal Regulation in Animals

Feedback Mechanisms in Biological Systems

1. Negative Feedback (Retroalimentación Negativa): It is one of the most common mechanisms to exert chemical regulation, where the final product of a chemical reaction inhibits the reaction that gave it origin.

2. Positive Feedback (Retroalimentación Positiva): The allosteric effect of the interaction of the metabolite with the primary reaction does not always have to be an inhibitor. A configuration change could also increase the reaction; i.e., the accumulation of the final product could accelerate the reaction from which it comes.

Homeothermic Animals

These animals have a very constant and usually high internal body temperature. The primary source of heat in them originates inside the cells of the body through the oxidation of glucose and other molecules that yield energy. The metabolism of homeotherms is much more intense than that of poikilotherms because they devote a large proportion of their energy to the production of heat.

Mechanisms of Regulation When Body Temperature Rises

As the body temperature of a mammal rises above the value set in the hypothalamus, the blood vessels near the surface of the skin dilate and the blood supply to the skin increases. If the air is cooler than the body surface, heat is transferred directly to the air.

Mechanisms of Regulation at Low Body Temperatures

When the temperature of circulating blood begins to fall below the value set in the hypothalamus, the blood vessels near the surface of the skin constrict, limiting cutaneous heat loss, while simultaneously intensifying metabolic processes.

Physiological Effects of Cold

When the temperature of a living being decreases, these reactions occur:

• The intensity of physiological processes decreases.
• The consumption of oxygen decreases.
• The movements become slower.
• The animal enters a state of dormancy or torpor.

Acclimation to High and Low Temperatures

There are extreme temperatures to which animals can acclimate up to a certain point, below which they do not tolerate the decrease in temperature.

Effects of Heat and Lethal Temperatures

Each species of animal has associated with itself a true index of thermal tolerance. Birds, reptiles, mammals, and insects have a lethal limit of 45°C. Aquatic animals have low thermal tolerance in comparison with land animals, and many die between 30°C and 35°C. Some arctic animals living at temperatures near freezing die if the temperature rises by 10°C.