Circulatory Systems in Animals

In animals that have efficient circulatory systems and readily permeable vascular skins, gas exchange occurs through the integument. Thus we find that animals like earthworms, leeches and many larval fishes are among the many animals that obtain the oxygen they need across their general body surface. Even larger animals such as many amphibians and fish may rely on cutaneous respiration during emergencies or use it as a supplement to the gills or lungs. The ability to respire through the integument developed the most in eels, and amphibians that have moist and highly vascularised skins.

The integumentary contribution to respiration may be as low as 20 per cent in dry-skinned toads to 76 per cent in the urodele Triturus alpestris and over 90 per cent in the giant salamander Cryptobranchus alleganiensis. This aquatic amphibian is the largest animal relying exclusively on integumentary breathing. The adults are 25 to 60 cm in length and may weigh over 1 kg. These animals lack gills and the lungs being unspecialised play little or no part in respiration. Animals that are large and have higher metabolic rates have specialised respiratory organs. These organs have a thin respiratory surface to help in gas exchange.