Frogs are amphibians known for their ability to thrive in both aquatic and terrestrial environments. This dual lifestyle is supported by an adaptable respiratory system, allowing them to extract oxygen from both air and water. Their unique features enable them to navigate diverse habitats.
Breathing Through Skin
Adult frogs primarily breathe underwater through cutaneous respiration, which involves gas exchange directly across their skin. This method is effective because frog skin is thin, highly permeable to water and gases, and richly supplied with blood vessels just beneath the surface.
Oxygen dissolved in the water diffuses across this moist skin into the frog’s bloodstream. Simultaneously, carbon dioxide diffuses out of the blood and is released into the surrounding water. This cutaneous breathing is important for adult frogs when submerged, during prolonged dives, or during hibernation. It serves as their main way to obtain oxygen fully underwater, compensating for lung limitations in an aquatic environment.
Other Respiratory Adaptations
While skin respiration is crucial underwater, adult frogs also have respiratory mechanisms for breathing on land. They use lungs primarily for aerial respiration. These lungs are simpler, sac-like structures compared to mammalian lungs, and frogs lack a diaphragm or ribs. Instead, they use buccal pumping, lowering the mouth floor to draw air in through nostrils, then raising it to force air into their lungs. This pulmonary respiration is less efficient than skin breathing for underwater oxygen uptake.
Young frogs, or tadpoles, have a distinct respiratory system adapted for their aquatic life. Tadpoles breathe using gills, similar to fish. These gills, often covered by a flap of skin, absorb dissolved oxygen from the water into their bloodstream. As tadpoles metamorphose into adult frogs, their gills degenerate, and lungs form, preparing them for life on land. Frogs can also perform some gas exchange through the moist lining of their mouth and throat, known as buccopharyngeal respiration.
Environmental Influences on Underwater Breathing
Several external factors influence a frog’s ability to breathe underwater through its skin. Water temperature is one factor; colder water generally holds more dissolved oxygen than warmer water. This means cutaneous respiration is more efficient in cooler aquatic environments, while higher temperatures reduce oxygen availability. The dissolved oxygen level in the water directly affects how much oxygen a frog can absorb. Stagnant or polluted water often has lower oxygen concentrations, posing a challenge for frogs and potentially limiting their ability to remain submerged.
The condition of a frog’s skin is also crucial for effective underwater breathing. The skin must remain moist and healthy for efficient gas exchange. Mucus glands secrete a slimy layer that maintains this moisture, preventing the skin from drying out. If a frog’s skin becomes dry, its ability to absorb oxygen is severely impaired, which can be fatal. A healthy, moist skin surface is crucial for a frog’s survival, especially when relying on cutaneous respiration underwater.