Cutaneous respiration, or cutaneous gas exchange (sometimes called skin breathing), is a form of respiration in which gas exchange occurs across the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

or outer

integument In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, Exoskeleton, shell, germ or Peel (fruit), rind. Etymology The term is derived from ''integumentum'', which is Latin for "a coverin ...

of an organism rather than gills or

lungs The lungs are the primary organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the backbone on either side of the heart. Their function in the respiratory syste ...

. Cutaneous respiration may be the sole method of gas exchange, or may accompany other forms, such as

ventilation Ventilation may refer to: * Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation ** Mechanical ventilation, in medicine, using artificial methods to assist breathing *** Respirator, a ma ...

. Cutaneous respiration occurs in a wide variety of organisms, including

insects Insects (from Latin ') are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed ...

amphibians Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

, sea snakes, turtles, and to a lesser extent in

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

Physical constraints

Gas exchange in cutaneous respiration is controlled by three factors: *

Ventilation Ventilation may refer to: * Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation ** Mechanical ventilation, in medicine, using artificial methods to assist breathing *** Respirator, a ma ...

: the rate of delivery of respiratory medium (water or air) to the respiratory surface *

Diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

: the passage of gases through the skin *

Convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...

: the carrying of dissolved gases towards or away from the lungs

Taxonomic diversity in chordates

Fish

Cutaneous respiration occurs in a variety of marine, intertidal, and freshwater fish. For

aquatic respiration Aquatic respiration is the Biological process, process whereby an aquatic animal, aquatic organism exchanges Respiration (physiology), respiratory gases with water, obtaining oxygen from oxygen dissolved in water and excretion, excreting carbon ...

, fish respire primarily via gills but cutaneous respiration may account for 5 to 40 percent of the total respiration, depending on species and temperature. Cutaneous respiration is more important in species that breathe air, such as mudskippers and reedfish, and in such species may account for almost 50 percent of total respiration.

Amphibians

The skin of

amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

s is a major site of respiration in all species for which measurements are available. Cutaneous respiration is the sole respiratory mode of lungless salamanders (family Plethodontidae) which lack lungs entirely yet constitute the largest family of salamanders. Cutaneous respiration in frogs and other amphibians may be the primary respiratory mode during colder temperatures. Some amphibians utilizing cutaneous respiration have extensive folds of skin to increase the rate of respiration. Examples include the hellbender salamander and the Lake Titicaca water frog. Cutaneous respiration in hellbenders accounts for more than 90 percent of oxygen uptake and carbon dioxide excretion.

Reptiles

Being covered in

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number ...

largely precludes cutaneous respiration in reptiles, but gas exchange may occur between scales or areas with reduced scales. Some turtles rely on cutaneous respiration from enteral respiration around the

cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

during underwater hibernation. In some sea snakes, cutaneous respiration can account for up to 30 percent of total oxygen uptake and is important when diving, during which blood is shunted away from the lungs and towards capillaries in the skin, in some cases causing the skin to turn pink.

Mammals

Mammals are endotherms, ("warm-blooded") and have higher metabolic demands than ectothermic ("cold-blooded") vertebrates, and the skin is thicker and more impermeable than other vertebrates, which preclude the skin as a major source of gas exchange. However, small amounts of respiration may occur, and in bats, the highly vascularized wings may account for up to 12 percent of carbon dioxide excretion. In humans and most other mammals, cutaneous respiration accounts for only 1 to 2 percent. A lot more respiration occurs through the skin in newborn marsupials. In the Julia Creek dunnart the newborns are extremely small, and 95% of their gas exchange happens via their skin.Skin structure in newborn marsupials with focus on cutaneous gas exchange
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References

{{reflist Respiration Skin