There are three living orders of amphibians. Amphibian's skin is smooth and moist and some caecilians have small scales embedded in the skin folds of the body. The inside of the skin of the amphibians has many blood vessels, which help with respiration. They also have mucous glands that keep the skin moist. Some have granular glands that secrete a fluid that is irritating and poisonous.
Skin color can change by expansion or contraction.
The outer part of the skin is continually being shed and renewed. Sometimes the skin is shed in large patches that may be eaten by the amphibian. Some salamanders can regenerate whole limbs. The digestive, skeletal, muscular, nervous, and other systems of amphibians are similar to those of higher animals. Because of this biology students study the frog to learn about these systems.