Abstract
The terminal respiratory units of the gas exchange tissue of the avian lung, the air capillaries (ACs) and the blood capillaries (BCs), are small and rigid: the basis of this mechanical feature has been highly contentious. Because the strength of the blood-gas barrier (BGB) of the mammalian lung has been attributed to the presence of type-IV collagen (T-IVc), localization of T-IVc in the basement membranes (BM) of the BGB and the epithelial-epithelial cell connections (E-ECCs) of the exchange tissue of the lung of the avian (chicken) lung was performed in order to determine whether it may likewise contribute to the strength of the BGB. T-IVc was localized in both the BM and the E-ECCs. As part of an integrated fibroskeletal scaffold on the lung, T-IVc may directly contribute to the strengths of the ACs and the BCs.