Warm-blooded
Encyclopedia
The term warm-blooded is a colloquial term to describe animal
species
which have a relatively higher blood temperature, and maintain thermal homeostasis
primarily through internal metabolic
processes. These are characteristics of mammal
s and bird
s.
Both the terms "warm-blooded" and "cold-blooded
" have fallen out of favour with scientists because of the vagueness of the terms and an increased understanding of the field. Body temperature
types are not discrete categories. Each term may be replaced with one or more variants, see the next section for examples. Body temperature maintenance (thermoregulation
) incorporates a wide range of different techniques that result in a body temperature continuum.
.
s and bird
s, fit all three of these categories. However, over the past 30 years, studies in the field of animal thermophysiology have revealed many species belonging to these two groups that do not fit all these criteria. For example, many bat
s and small birds are poikilothermic and bradymetabolic
when they sleep for the night, or day, as the case may be. For these creatures, the term heterothermy was coined.
Further studies on animals that were traditionally assumed to be cold-blooded
have shown that most creatures incorporate different variations of the three terms defined above, along with their counterparts (ectothermy, poikilothermy and bradymetabolism
), thus creating a broad spectrum of body temperature types. Even some fish
have warm-blooded characteristics. Swordfish
and some shark
s have circulatory
mechanisms that keep their brain
s and eye
s above ambient temperatures, and thus increase their ability to detect and react to prey
. Tunas and some sharks have similar mechanisms in their muscles, improving their stamina when swimming at high speed.
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
which have a relatively higher blood temperature, and maintain thermal homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
primarily through internal metabolic
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
processes. These are characteristics of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s and bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s.
Both the terms "warm-blooded" and "cold-blooded
Cold-blooded
Cold-blooded may refer to:* ectothermy, controlling body temperature through external means, such as by basking in the sun* poikilothermy, the ability of an organism to function over a wide internal temperature range...
" have fallen out of favour with scientists because of the vagueness of the terms and an increased understanding of the field. Body temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
types are not discrete categories. Each term may be replaced with one or more variants, see the next section for examples. Body temperature maintenance (thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
) incorporates a wide range of different techniques that result in a body temperature continuum.
Characteristics of warm-bloodedness
Warm-bloodedness generally refers to three separate aspects of thermoregulationThermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
.
- EndothermyEndothermAn endotherm is an organism that produces heat through internal means, such as muscle shivering or increasing its metabolism...
is the ability of some creatures to control their body temperatures through internal means such as muscle shivering or increasing their metabolismMetabolismMetabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
(Greek: endon = "within", thermē = "heat"). Some writers restrict the meaning of endothermy to mechanisms that directly raise the animal's metabolic rate in order to produce heat. The opposite of endothermy is ectothermy. - HomeothermyHomeothermHomeothermy is thermoregulation that maintains a stable internal body temperature regardless of external influence. This temperature is often, though not necessarily, higher than the immediate environment...
is thermoregulation that maintains a stable internal body temperature regardless of external influence. This temperature is often, though not necessarily, higher than the immediate environment (Greek: homoios = "similar", thermē = "heat"). The opposite is poikilothermy. - Tachymetabolism is the kind of thermoregulation used by creatures that maintain a high "resting" metabolism (Greek: tachys/tachus = "fast, swift", metabolēn = "throw beyond"). Tachymetabolic creatures are, essentially, "on" all the time. Though their resting metabolism is still many times slower than their active metabolism, the difference is often not as large as that seen in bradymetabolicBradymetabolismBradymetabolism refers to organisms with a high active metabolism and a considerably slower resting metabolism. Bradymetabolic animals can often undergo dramatic changes in metabolic speed, according to food availability and temperature...
creatures. Tachymetabolic creatures have greater difficulty dealing with a scarcity of food.
Reasons for term falling into disuse
A large proportion of the creatures traditionally called "warm-blooded", such as mammalMammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s and bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, fit all three of these categories. However, over the past 30 years, studies in the field of animal thermophysiology have revealed many species belonging to these two groups that do not fit all these criteria. For example, many bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...
s and small birds are poikilothermic and bradymetabolic
Bradymetabolism
Bradymetabolism refers to organisms with a high active metabolism and a considerably slower resting metabolism. Bradymetabolic animals can often undergo dramatic changes in metabolic speed, according to food availability and temperature...
when they sleep for the night, or day, as the case may be. For these creatures, the term heterothermy was coined.
Further studies on animals that were traditionally assumed to be cold-blooded
Cold-blooded
Cold-blooded may refer to:* ectothermy, controlling body temperature through external means, such as by basking in the sun* poikilothermy, the ability of an organism to function over a wide internal temperature range...
have shown that most creatures incorporate different variations of the three terms defined above, along with their counterparts (ectothermy, poikilothermy and bradymetabolism
Bradymetabolism
Bradymetabolism refers to organisms with a high active metabolism and a considerably slower resting metabolism. Bradymetabolic animals can often undergo dramatic changes in metabolic speed, according to food availability and temperature...
), thus creating a broad spectrum of body temperature types. Even some fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
have warm-blooded characteristics. Swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...
and some shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s have circulatory
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
mechanisms that keep their brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
s and eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
s above ambient temperatures, and thus increase their ability to detect and react to prey
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
. Tunas and some sharks have similar mechanisms in their muscles, improving their stamina when swimming at high speed.