Cutaneous respiration, or cutaneous gas exchange, is a form of respiration in which gas exchange occurs across the skin or outer integument of an organism rather than gills or lungs.
Cutaneous respiration means breathing through the skin.
Amphibians, you may recall, are vertebrate animals (those having a backbone) that complete a portion of their life cycle in water and another portion on land. There are also some completely aquatic, or water-living, amphibians. Because of their dependence on water, many amphibians have retained the traits of their ancestors, including reduced or even absent lungs. Many rely on breathing through the skin, cutaneous respiration, for some or their entire oxygen intake, and especially for carbon dioxide output.
The trait of cutaneous respiration is present in all three groups of amphibians:
• Caudata (salamanders and newts),
• Anura (frogs and toads), and
• Caecilians (uniquely legless amphibians).
How Does Cutaneous Respiration Work?
• Cutaneous respiration occurs by way of countercurrent exchange, where blood circulating through the skin flows in the opposite direction of the absorbing oxygen or surrounding water. Think of countercurrent exchange as two pipes pressed parallel together, with water flowing through at the same speed. Water in one tube is hot, and flows in one direction, and water in the other tube is cold, flowing in the opposite (counter) direction. If the tubes are made of conductive material, like metal, and contact one another, heat will pass across one tube to the other.
• This is similar to crosscurrent exchange, which bird lungs use to pick up oxygen. Blood capillaries branch across an air capillary at right angles, almost as if they were wrapped around one another. In contrast, our own lungs also pass carbon dioxide and oxygen between blood capillaries and in the tiny spaces in our lungs, but these transfers are across a gradient.
A frog is an amphibian, but adult frogs do not have gills. They absorb oxygen from the water through their skins, using special blood vessels. If the oxygen level in water is too low, frogs will move around to increase the water flow across the skin. Some frogs have creased skins that can increase their surface area.
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