Amphibians are vertebrates that belong to the Amphibia class of ectothermic animals.
Amphibians thrive in aquatic, terrestrial, and other habitats and begin their life in the form of larvae. The amphibia class is further divided into three orders, which are the Anura, Urodela, and Apoda.
The Anura class contains tailless, four-legged carnivores like frogs and toads. These animals are found in a large number all across the world. The Uroedela class contains various salamander and newt species that are known for their long bodies and short limbs projecting out from these long bodies. Salamanders and newts are commonly found in the Northern hemisphere of the world and even though they look like they are related to reptiles, they are certainly not one of the many reptiles found across the world. The final class of the Amphibia order is the Apoda order, which contains caecilians. Caecilians are amphibians that look like earthworms as they lack limbs and are blind and are housed in the tropical forests.
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How do amphibians breathe on land?
On land, amphibians breathe through their lungs and skin as they take air into the lungs through their nostrils.
In most cases of amphibians, especially in cold-blooded animals like adult frogs, the respiration is done through the lungs and the skin. Frogs and toads keep their skin moist by secreting mucous through their mucus glands, which helps them in absorbing oxygen through the skin. The oxygen absorbed by these animals will enter their respiratory system and enter the blood vessels at the surface of the skin that will help in circulating oxygen to the body. In most terrestrial amphibian species like the lungless salamanders, the oxygen is absorbed through the skin as they do not have lungs. Aquatic amphibians like tadpoles have fish-like gills that play an active role in the underwater breathing process.
The process of breathing through the skin in adults is known as cutaneous respiration or buccal pumping, and in some cases, the adults retain the gills that they develop in their larval stage. Compared to mammals, birds, and reptiles, amphibians have primitive lungs, which result in a slow oxygen diffusion. Not to forget, 75% of the amphibian skin is covered by capillaries. These capillaries help in carrying the oxygen through the blood vessels and into the cells and help in dumping carbon dioxide.
Cutaneous respiration is also helpful in many amphibians like many species of salamanders, along with frogs and toads as their moist skin is kept moist by absorbing water through the surface area of the skin. The frog's permeable skin keeps the animal from suffocating.
The method of buccal pumping is a common occurrence in the toad and frog species as adult frogs breathe air in through nostrils and push the breath through the lungs as they contract their throat since they lack a diaphragm.
How do amphibians breathe underwater?
Amphibians breathe under the water through their gills and their skin.
When in a larval stage, all aquatic and terrestrial amphibians breathe underwater, for example, frogs, toads, and salamanders. As these animals go through metamorphosis and develop from larvae to full-grown animals, some might lose the gills, which leads to them not being able to breathe underwater. Out of the lungs, skin, and gills, only the skin and gills', which act as the respiratory parts, can be seen.
Many amphibian species need to come to the surface for their oxygen intake when they are exhausting their bodies. In the case of a resting state, the oxygen demand for animals like tadpoles, frogs, and salamanders can be easily met underwater. Frogs and toads have various methods that have evolved as they developed a respiratory cover on the lining of their mouth where the gas exchange takes place. There are a handful of amphibian classes that cannot breathe underwater but can hold their breath for hours.
What type of respiratory system do amphibians have?
Amphibians, especially terrestrial and aquatic frog species have their own method of pumping oxygen into their bodies.
In the larval stage as tadpoles, frogs breathe through their gills. As these tadpoles grow, the resulting adult will either retain the gill, lose the gills to develop lungs or use their gills and lungs to breathe. Some amphibians have none of these and use cutaneous respiration throughout their life.
Unlike reptiles and salamanders, frogs have three respiratory surfaces in the body, which are the skin, the lungs, and the lining of the mouth. When frogs are more aquatic than terrestrial they take in oxygen through the skin and exhume carbon dioxide. The skin of the adult frogs is made up of thin membrane tissues that are permeable to water and have blood vessels in them.
When frogs are on land, they secrete mucus through their glands, which helps in keeping this amphibian moist, the gland in return will help the frogs in absorbing oxygen from the air. Just like in the case of humans, frogs too can breathe with their lungs as they take in air through the nostrils, which goes down into the lungs. Since frogs do not have a diaphragm or ribs, they draw air through the mouth as they lower the mouth floor which causes an expansion in the throat. The nostrils are opened to allow air to follow into the mouth. The nostril is then closed and the air in the mouth goes down the throat as the mouth floor contracts. Frogs, to eliminate the amount of carbon dioxide in the air, will move their mouth down, which draws the air from the lungs into the mouth. The nostrils are opened at the final step as the mouth floor pushes the air out of the nostrils.
Frogs are also known to have a respiratory surface that is present on the lining of the mouth where the exchange of gas takes place. In the resting form, this gas exchange is the dominant breathing form as it fills the surface area of the lungs well enough for proper blood flow in the adult.
Do amphibians have lungs?
Amphibian species are often divided into aquatic and surface dwellers, and as a direct result of this lifestyle, may or may not develop lungs depending on the species they belong to.
As vertebrates, amphibians need to control the temperature of their bodies but have to rely on their surroundings for that. Since amphibians are the earliest descendants of fishes, the beginning of their life is in water, using their gills for breathing. As they develop, most amphibians like frogs, maintain the ability to live in water as they intake oxygen through their skins, which they have done as tadpoles and larvae. Some species can turn into land dwellers and will develop lungs to breathe on land.
The lungs of amphibians are less complex than that of humans as they lack the diaphragm that assists in the breathing process. These animals intake air through the nostril into their mouth which eventually flows down their throat, the muscles expand and contract for the gas exchange to take place in the lungs.
In some instances, amphibians do not acquire lungs like growing tadpoles and will continue to live their life without the presence of lungs as the breathing process is carried on by the gas exchange through the skin pores. The lungless salamander is an example of an animal that does not acquire lungs as they grow up and breathe through their skin or gills for the rest of their life.
Amphibians: How They Originated
Amphibians are one of the oldest classes of animals found in the world and their origin can be dated back to the Devonian period that spanned between 419.2 million and 358.9 million years ago approximately.
Amphibians have evolved over the history of the Earth as their evolution began with the movement of a lobe-finned fish from water to the surface. These large four-limbed tetrapods set the precedent for the amphibians and larger vertebrates of today that went on to produce descendants that still exist to this day.
The Eucritta and Crassigyrinus are the first known amphibians to spawn on the surface after their predecessors left the water. Since these amphibians were on the larger scale, they dominated the Earth for millions of years but were eventually overthrown by the reptile family that led to the rise of dinosaurs and large mammals like the Therapsid class.
The Eryops was the largest known amphibian of its time as it grew up to 2.7 ft (9 m) in body length and weighed between 200-400 lb (90.7-181.4 kg).
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