Endotherms use metabolic heat production to maintain constant high body temperatures. Body temperatures of ectotherms are more dependent on environmental heat sources. Both ectotherms and endotherms use behavior to control their body temperature. Heat exchange between an animal and its environment occurs via radiation, convection, conduction, and evaporation, all of which depend on body surface temperature. Some ectotherms use metabolic heat production episodically to raise body temperature.
learning outcomes
You should be able to:
Explain responses to environmental temperature by an ectotherm, an endotherm, and a heterotherm.
Describe the paths of heat exchange between an animal and its environment.
Explain the principle of countercurrent heat exchange.
Why is the body temperature of an ectotherm that is exposed to variations in environmental temperature more constant in nature than in the laboratory?
In nature, the ectotherm can use behavioral adaptations such as basking and seeking shade to prevent significant changes in its body temperature. In the laboratory, it does not have the opportunity to bring those adaptations into play.
For each path of heat exchange, what determines whether heat is gained or lost by the animal?
The animal gains heat from radiation, convection, or conduction if the environment is warmer than the surface temperature of the animal, and the animal loses heat if the environment is cooler than the surface temperature of the animal. Evaporation can only result in a loss of heat from the animal, and the magnitude of the loss depends on the amount of water that is evaporated on a heat exchange surface such as skin or respiratory passages.
Compared to most fishes, explain the circulatory system adaptations that enable “hot” fishes to raise the temperature of their swimming muscles.
In fish, the blood leaving the heart goes to the gills, where it comes into temperature equilibrium with the surrounding water. In most fish, that blood flows down the center of the fish through a large vessel leading to lots of smaller vessels that perfuse the tissues of the fish, thus cooling those tissues. In “hot” fish, the major blood flow from the gills is through peripheral vessels that give rise to smaller segmental vessels going into the muscle tissue. The vessels carrying blood in (arteries) run parallel and close to the vessels carrying blood out (veins). The veins carry heat produced in the muscle, but because of this countercurrent flow of blood in the arteries and veins, the heat from the venous blood warms the arterial blood flowing into the muscle, thus decreasing the loss of heat from the muscle tissue. Countercurrent heat exchange in “hot” fish acts to keep the heat generated by the powerful swimming muscles in the muscle tissue.
Endotherms respond to changes in environmental temperature by changing their rates of metabolic heat production. They also have other adaptations for controlling their rates of heat exchange with their environments. How do they regulate these various avenues of heat exchange to achieve a constant internal body temperature?