The lungs of most frogs and other amphibians are simple balloon-like structures, with gas exchange limited to the outer surface area of the lung. This is not a very efficient arrangement, but amphibians have low metabolic demands and also frequently supplement their oxygen supply by diffusion across the moist outer skin of their bodies. Unlike mammals, which use a breathing system driven by negative pressure, amphibians employ positive pressure. The majority of salamander species are lungless salamanders which conduct respiration through their skin and the tissues lining their mouth. The only other known lungless tetrapods are also amphibians; the Bornean Flat-headed Frog (Barbourula kalimantanensis) and Atretochoana eiselti, a caecilian.
The lungs of amphibians typically have a few narrow septa of soft tissue around the outer walls, increasing the respiratory surface area and giving the lung a honey-comb appearance. In some salamanders, even these are lacking, and the lung has a smooth wall. In caecilians, as in snakes, only the right lung attains any size or development.
Adult frogs obtain oxygen and release carbon dioxide (respiration) in a number of different ways. Frog lungs are not as good as those found in birds, reptiles and mammals, so they need to help this breathing by using two other types of respiration. Gas exchange can occur across the roof of the mouth (this is called ‘buccal’ or ‘buccopharyngeal’ respiration) and directly across the skin (this is called ‘cutaneous’ respiration). The three different methods of respiration are used in different amounts depending on what type of frog it is, what it is doing and what time of year it is.
Using their mouth
The roof of the mouth is richly lined with blood vessels that are able to extract oxygen from the air. The constant movements of the frog’s throat are used to bring air in through the nose and across the roof of the mouth, where oxygen is absorbed and carbon dioxide is removed. The air is then released through the nose. During this process, the passage to the lungs is kept closed. This type of respiration may account for up to 10% of a frog’s gas exchange.
Using their lungs
Frogs do not have ribs or a diaphragm and, unlike mammals, they are not able to use them to change the internal pressure and ventilate the lungs. To get past this problem, frogs inflate their lungs in stages by closing them off and bringing air into their throat via their nose. They then block off their nose, pass the air from the throat into their lungs, close their lungs off and bring in more air through their nose. This process is repeated a few times until the lungs are inflated. Once the lungs are fully inflated, gas exchange occurs across the lungs and the used-up air is then released through the nose (in a stream over the top of some more fresh air that is brought into the throat). Some frogs will also lift their eyes to increase the space available inside the throat to allow more air in! This is why you can usually see a frog’s throat moving in and out.
Using their skin
Frog skin has a number of special features that help it to function as a respiratory surface. Frog skin is very loose and thin and it contains an extensive network of blood vessels. By keeping the skin moist, frogs allow gases to pass directly between the blood vessels and the outside. If the skin is dry, this method of breathing does not function very well, so most frogs have special glands in their skin that produce a mucous to keep them moist. Frogs are able to breathe on land or underwater using cutaneous respiration! Unfortunately, this sort of breathing is only effective in small animals, which probably explains why most frogs are relatively small.
The lungs of amphibians typically have a few narrow septa of soft tissue around the outer walls, increasing the respiratory surface area and giving the lung a honey-comb appearance. In some salamanders, even these are lacking, and the lung has a smooth wall. In caecilians, as in snakes, only the right lung attains any size or development.
Adult frogs obtain oxygen and release carbon dioxide (respiration) in a number of different ways. Frog lungs are not as good as those found in birds, reptiles and mammals, so they need to help this breathing by using two other types of respiration. Gas exchange can occur across the roof of the mouth (this is called ‘buccal’ or ‘buccopharyngeal’ respiration) and directly across the skin (this is called ‘cutaneous’ respiration). The three different methods of respiration are used in different amounts depending on what type of frog it is, what it is doing and what time of year it is.
Using their mouth
The roof of the mouth is richly lined with blood vessels that are able to extract oxygen from the air. The constant movements of the frog’s throat are used to bring air in through the nose and across the roof of the mouth, where oxygen is absorbed and carbon dioxide is removed. The air is then released through the nose. During this process, the passage to the lungs is kept closed. This type of respiration may account for up to 10% of a frog’s gas exchange.
Using their lungs
Frogs do not have ribs or a diaphragm and, unlike mammals, they are not able to use them to change the internal pressure and ventilate the lungs. To get past this problem, frogs inflate their lungs in stages by closing them off and bringing air into their throat via their nose. They then block off their nose, pass the air from the throat into their lungs, close their lungs off and bring in more air through their nose. This process is repeated a few times until the lungs are inflated. Once the lungs are fully inflated, gas exchange occurs across the lungs and the used-up air is then released through the nose (in a stream over the top of some more fresh air that is brought into the throat). Some frogs will also lift their eyes to increase the space available inside the throat to allow more air in! This is why you can usually see a frog’s throat moving in and out.
Using their skin
Frog skin has a number of special features that help it to function as a respiratory surface. Frog skin is very loose and thin and it contains an extensive network of blood vessels. By keeping the skin moist, frogs allow gases to pass directly between the blood vessels and the outside. If the skin is dry, this method of breathing does not function very well, so most frogs have special glands in their skin that produce a mucous to keep them moist. Frogs are able to breathe on land or underwater using cutaneous respiration! Unfortunately, this sort of breathing is only effective in small animals, which probably explains why most frogs are relatively small.