What is skin respiration?

The Cutaneous respiration Is a form of respiration in which gas exchange occurs through the skin and not through the lungs or gills.

This process occurs mainly in insects, amphibians, fish, sea snakes, turtles and some mammals (Jabde, 2005).

Toad. An example of an animal with skin breathing.

The skin of animals that use skin breathing is quite special. To allow for a gaseous exchange, it must be wet so that both oxygen and carbon dioxide can pass freely through it.

The skin breathing process is performed only through the skin. For this reason, most vertebrates that use this type of breathing, the skin is highly vascularized in order to facilitate the gas exchange process.

This exchange is highly important in amphibians and soft-shelled turtles, which use mucus glands to preserve skin moisture (Marshall, 1980).

Some amphibians have many folds on their skin that help them increase their breathing rate. Toads are known for drinking water and breathing through the skin. They have three forms of breathing: cutaneous, pulmonary and through the lining of the mouth. This last type of breathing is the most used when they are in rest state.

Cutaneous breathing is a type of breathing that does not need the lungs to be performed. For this reason, there are species that lack lungs and can still survive thanks to the gas exchange performed through the skin.

There are species that can exert both skin and lung breathing, however, it is estimated that in amphibians the skin is responsible for taking 90% of the oxygen needed to live.

Skin respiration in different classes of animals

Amphibians

The skin of all species of Amphibians Is the organ most used to carry out the breathing process. Some species depend only on skin respiration to survive.

This is the case of the family's salamander Plethodontidae . This family of amphibians is completely devoid of lungs, however, it forms the largest group of salamanders in the world. (Zahn, 2012)

While amphibians are completely immersed in water, skin breathing takes place through their skin. This is a porous membrane by means of which the air extends between the blood vessels and everything that surrounds them.

Although cutaneous respiration is predominant in amphibians, it only helps the survival of toads during colder seasons.

Skin respiration requires constant moisture on the surface of the skin. When the toads are out of the water, the mucous glands in the skin continue to moisten it, which allows a process to absorb oxygen from the air.

There are some special cases in amphibian respiration. For example, tadpoles, which breathe through gills, and desert toads, which tend to have dry skin, so that skin respiration is not feasible (Bosch, 2016).

Reptiles

The scales that cover the body of the Reptiles Prevents, in most cases, a process of skin respiration.

However, there is the possibility of gaseous exchange between scales or areas where the density of scales is less.

During periods of underwater hibernation, some turtles rely on skin respiration around the sewer to survive.

Similarly, there are species of marine snakes that take approximately 30% of the oxygen they need through the skin. This becomes critical when you need to dive underwater.

For marine snakes it is possible to perform this process by decreasing the intensity with which the blood feeds the lungs and increase the blood supply in the capillaries of the skin. For this reason, the skin of snakes can sometimes give a pink appearance. (Feder & Burggren, 1985)

Mammals

Mammals are known to be species Endothermic Or"hot blood". They generally have a higher metabolic demand than exothermic or"cold-blooded"vertebrates.

Similarly, the skin of mammals is thicker and impermeable than other vertebrate species, which greatly prevents the skin from being the organ used to perform the gas exchange process.

However, skin respiration in mammals exists, but occurs in a lower percentage. One example is bats, which take oxygen through the highly vascularized membranes located in their wings. Bats can take about 12% of the oxygen they need through their wings.

Humans are among the species of mammals that have less percentage of oxygen taken from the air through the skin. A human being can take on average between 1% and 2% of oxygen in the air, so that it could not guarantee its subsistence (Ernstene & Volk, 1932).

Insects

In insects, gaseous exchange through the skin tends to be generous but does not represent the primary source of oxygen uptake.

Most insects take oxygen and shed carbon dioxide through a tissue known as cuticle , Which is located in the outermost part of the invertebrate epidermis.

There are some families of insects that do not have a defined respiratory system, so they are completely dependent on cutaneous respiration to transport the Hemolymph (Similar to blood in insects) from the surface of the body to the internal tissues.

Most terrestrial insects use a trachea system to perform gas exchange. However, in aquatic and endoparasitic insects, skin respiration is vital, as its tracheal system can not deliver the oxygen required alone (Chapman, 1998).

Fishes

Skin respiration occurs in different species of marine and freshwater fish. For aquatic respiration, fish mainly require the use of gills.

However, cutaneous respiration represents between 5% and 40% of the total oxygen uptake of water, although all this depends on the species and the temperature of the medium.

Skin respiration is more important in species that take oxygen from the air like jumping fish or coral fish. In these species, oxygen uptake through the skin accounts for 50% of total respiration.

References

1. Bosch, D.L. (7 of 2, 2016). All you need is Biology. Retrieved from How To Breathe Without Lungs, Lissamphibian Style: allyouneedisbiology.wordpress.com.
2. Chapman, R.F. (1998). Cutaneus Respiration. In R. F. Chapman, The Insects: Structure and Function (page 452). New York: Cambridge University Press.
3. Ornstein, A.C., & Volk, M.C. (1932). The Effect of Venous Congestion on the Rate of Carbon Dioxide Elimination and Oxygen Absorption. The Journal of Clinical Investigation, 387-390.
4. Feder, M. E., & Burggren, W. W. (1985). Cutaneous Gas Exchange In Vertebrates: Design, Patterns, Control And Implications. Biological Reviews, 1-45.
5. Jabde, P. V. (2005). Respriation. In P. V. Jabde, Text Book Of General Physiology (page 112). New Dehli: Discovery Publishing House.
6. Marshall, P. T. (1980). Restriction, Gas Exchange and Transport. In P. T. Marshall, Physiology of Mammals and Other Vertebrates (pp. 88-89). New York: Cambridge University Press.
7. Zahn, N. (24 of 8 of 2012). Retrieved from Salameandering Into Cutaneous Respiration: iheartungulates.com.