A warm-blooded is a living specie that will keep a stable body temperature, in certain specific limits, independently to the exterior temperature. It can be also referred as thermic homeostasis. Human beings are warm-blooded for example.
Humans beings are also endotherms, so they can produce internally heat (opposed to ectotherm). An important variation of temperature will be lethal for members of this group. And in order to maintain their internal body temperature at the right one, they will need to bring a lot of energy so a lot of oxygen and be feed regularly and in quite important quantities.
Warm-blooded organisms are opposed to poikilotherms, that are those having internal temperature changing with ambient temperature. For example, lizards are part of this category.
As for ectotherms, are organisms that cannot produce internal heat. They depend on exterior sources of heat to increase their temperature. It’s the case of reptiles, insects and fishes. Ectotherms can be warm-blooded or poikilotherms.
Some animals don’t fit in a category because they have a partial heating regulation. For example, tuna or some sharks can regulate some of their organs ‘temperature to be more efficient predators when they hunt in cold waters.
It can be asked, why our body are at 37 °C as human beings are warm-blooded?
It’s the perfect temperature for metabolic reactions of body. It’s the perfect temperature for biochemical reactions to occur at the right intensity and with enough speed without damaging cells.
This capacity of the body to always be at an approximately temperature of 37 °C is linked to the biological phenomenon called thermoregulation. Thermoregulation is the group of phenomena allowing to maintain a stable temperature of an organism. This phenomenon gathers mechanisms of production (thermogenesis) and dissipation (thermal decomposition) of heat.
When thermal regulation is not reached, organism will be affected and enter in hypothermia (when central temperature is inferior to normal temperature), or in hyperthermia (when central temperature is superior to normal temperature).
The organ the most involved in the regulation of body temperature is the brain and more specifically hypothalamus. This organ is going to play a role of thermostat. For example, when it is warm, it sends a message to the brain to dilate blood vessels and induce sweating. This phenomenon allows to release some body heat and regulate temperature. When it is cold, the hypothalamus sends a message to muscles, so they contract and produce heat that are expressed as shivers.
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