| The high incidence of immature lungs in premature infants necessitates the development of therapeutic and prophylactic regimes to improve the capacity of the neonatal lung for gas exchange, through study of structural and functional lung development in animal models. The objectives of this dissertation were firstly, to define the stages of lung development present during periods of fetal and neonatal life in the dog and/or pig and secondly, to calculate the morphometric diffusion capacity of the lung, (D(,LO2)), an indicator of lung structure and function, in the adult dog and neonatal dog and pig.;Non-ciliated bronchiolar cells were identified in the fetal dogs and neonatal dogs and pigs. Characterized at the TEM level by a sparse complement of cytoplasmic organelles, few mitochondria and occasional rosettes of glycogen, these cells were believed to be immature bronchiolar exocrine (Clara) cells.;Samples were collected from tracheally-instilled, glutaraldehyde-fixed lungs, prepared routinely for light and transmission electron microscopic examination and the morphometric D(,LO2) calculated using the principles of stereology. The D(,LO2) of the neonatal pig was found to be significantly greater than that of the neonatal dog (P < 0.05). A simlar species difference was noted in the lung volume and body weight data, however, when standardized for body weight, the lung volume of the dog was found to be greater than that of the pig. This may reflect a structural design of the lung that provides sufficient gas exchange to support the relatively high metabolic activity of the neonatal animals.;Lung tissue was collected from two litters of fetal dogs that were determined, by carcass measurements, to have undergone 33 days and 54 days of gestation, respectively. Examination at the light and scanning electron microscopic levels revealed the early canine fetal lung to be in the pseudoglandular stage of lung development. The late canine fetal lung tissue was found to be in the late saccular or early alveolar stage of lung development. |
