How Do Amphibians Breathe?

Amphibians are excellent swimmers, spending long periods submerged below the water surface. It is natural to assume that they can breathe underwater, but this is inaccurate in most cases.

Amphibians breathe using their lungs, and many absorb oxygen through their skin. Oxygen enters the skin through blood vessels and circulates to the rest of the body. Amphibians use mucous to keep their skin moist. If their skin is not kept moist, then they will die.

If you want to learn more about how amphibians breathe, please read on.

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What Is An Amphibian

The term ‘amphibian’ is a class of animals. Within the natural world, animals are broken down into several taxonomic classifications, including domain, kingdom, phylum, class, order, family, genus, and species.

The two largest classifications are domain and kingdom. The domain encompasses all life on Earth. There are three domains; bacteria, archaea (single-celled organisms without a nucleus), and eukarya (organisms with a ‘true’ nucleus).

The kingdoms determine how organisms reproduce and how they acquire nutrients. The six kingdoms are Archaebacteria (single-celled organisms), Eubacteria (true bacteria), Protista (organisms with a nucleus enclosed within a membrane), Fungi (yeast, moulds and mushrooms), Plantae (all plants and vegetation), and Animalia (multi-celled animal organisms).

At each rank lower on the taxonomical scale, animals will be filtered into smaller groups. Species can belong to several different taxonomic groups.

Amphibians belong to Eukarya, kingdom Animalia, phylum Chordata, and class Amphibia. Animals within the class Amphibia share the following characteristics:

  • Ability to survive on land and in water
  • The body is easily divided into a head and a trunk.
  • Animals in this class are ectothermic (using the environment to control body temperature)
  • Smooth skin, glands to provide moisture, no scales
  • Three-chambered heart
  • Sexes are distinguishable; reproduction is mostly external
  • Breeding occurs in water
  • Respiration occurs via the lungs and skin
  • Two pairs of limbs

Amphibious species include frogs, toads, newts, and salamanders. The order Anura covers all modern frog and toad species. Urodela is the order to which newts and salamanders belong.

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Differences Between Juvenile and Adult

While most mammalian young look like smaller versions of their adult parents, the offspring of amphibians are different from their adult counterparts.

Most amphibians lay jelly-like eggs in water sources. Toads lay strings of eggs attached by membranous tissue. Frogs lay large clutches of eggs. Amphibian eggs are called spawn, the most common being frogspawn.

Egg development happens in aquatic environments, except for a small number of frogs that lay eggs on land.

Upon hatching, most amphibians are in a larval form. During their early development, they go through a period of growth and metamorphosis. For example, when frogspawn hatch, the young are called tadpoles. They look like a dark pea with a tail. During the first few weeks after hatching, tadpoles slowly develop their limbs and body shape while their internal organs develop to support an adult diet. During this time, the tail gradually recedes.

Juveniles spend all their time underwater and cannot survive long on land. By contrast, adult amphibians can survive both in water and on land. During metamorphosis, they develop their lung structure to breathe air, but they can also synthesize oxygen via their skin.

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Amphibious Respiration

Eggs require oxygen to survive and grow. They acquire oxygen via respiratory gas exchange. This occurs via the movement of oxygen across the membrane surrounding the eggs. After hatching, larval amphibians acquire their oxygen via exchanges through their permeable skin. The larvae also have primitive gills used for oxygen exchange in some species.

Tadpoles are also able to use their tails for respiration. The blood vessels found in tadpole tails have a large surface area so that oxygen can pass straight into the blood.

As the larval stage progresses, the lungs will develop. At this point, tadpoles that have grown their limbs will begin making short trips onto land to breathe air via their lungs. Unlike mammals and birds, amphibian lungs are primitive, saclike structures.

Once an amphibious animal reaches adulthood, its larval gills are no longer necessary, and the lungs assume the primary respiratory function. In a small number of species, the adult form is similar to the juvenile stage of life. Axolotls are a perfect example. They have a head and long body with a tail and underdeveloped limbs. They also have frilled gills and do not breathe air at the water surface.

Capillary respiration

Each species has a different respiratory capillary surface area. This describes the surface area within the body where respiration takes place. For example, newts have approximately 75% of their capillary respiratory surface area on their skin. In contrast, certain tree frog species have most of their capillary respiratory surface area in their lungs.

Cutaneous respiration

Some amphibious species can use both cutaneous (skin) respiration and lung respiration, although they will use one much more than the other. Species that live in temperate climates experiencing cold seasons will rely on cutaneous respiration during the winter. Many species will burrow underground, which makes lung respiration almost impossible.

During cold weather, the metabolic processes slow down, meaning less oxygen is required. This means amphibians can rely solely on cutaneous respiration via the skin for extended periods.

Lung respiration

Lung respiration is achieved by buccal pumping. The floor of the mouth is depressed, which draws air into the mouth cavity via the nostrils. When the nostrils are closed, the floor of the mouth is raised. This creates a positive pressure within the mouth cavity and pushes air into the lungs.

Exhaling occurs via a different process. The muscles of the body contract, producing an elastic recoil of the lungs. This drives air out of the lungs but can also be assisted by water pressure acting on the outside of the animal’s body.

This is one of the reasons you should not handle a frog or toad unless you have to. By picking up the animal and holding it in your hand, you create pressure against the body, expelling air from the lungs. This can interfere with the animal’s natural breathing rhythm and would be understandably stressful for the animal.

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