Ultrastructural and morphometric changes in the lung of newt, Triturus cristatus carnifex Laur. during ontogeny

Ultrastructural and morphometric studies of the lungs in the newt, Triturus cristatus carnifex Laur, were performed at three stages of its life cycle: during metamorphosis; 2 to 3 weeks after metamorphosis; and in adult individuals. The lungs have the form of simple sacs, devoid of septa and lined with one type of respiratory epithelial cells. Ciliated and goblet cells are localized exclusively along the pulmonary vein. During the period from metamorphosis to sexual maturity (2 to 3 years) the number of respiratory epithelial cells increases, the cells change their shape and become embedded into connective tissue. In their cytoplasm appear lamellar and multivesicular bodies, and the amount of other organelles increases. The ciliated epithelium transforms from simple to pseudostratified type. The capillaries, initially flat and wide, gradually protrude into the lung lumen and the air-blood barrier increases in thickness, as does also the whole lung wall.