Study of Intrasegmental Branching Pattern of the Bronchial Tree in Fetuses and Estimation of Approximate Time of Appearance of Type II Pneumocytes

A study of the intrasegmental branching pattern of the bronchial tree was done in 50 spontaneously aborted fetuses from 10 weeks to 39 weeks of gestation. The fetuses were fixed with 10% Formalin and the lungs were removed from the fetuses. The external appearance of the lungs was observed. The weight of both the lungs was measured in fetuses. The oblique fissure in both the lungs did not show any variations but the horizontal fissure was observed to have variations. The bronchopulmonary segments were studied in the left lung of fetuses in age group of 20 to 39 weeks of gestation. The microscopic appearance was studied in the lower lobe of right lung in the fetuses by using Haemotoxylin and Eosin staining method. The variations in the time of appearance of cartilage, lining epithelium of bronchi and type II pneumocytes were observed. Knowledge of these variations are important for Anatomists, Cardiothoracic surgeons, Pulmonologists, Pediatricians, Obstetricians and Gynecologists. SUMMARY: A study of the intrasegmental branching pattern of the bronchial tree was done with 50 spontaneously aborted fetuses. The fetuses were fixed with 10% Formalin. The lungs were removed from the fetuses. The external appearances of the lungs were observed. The weight of the both lungs was measured in fetuses of 10 weeks to 39 weeks of gestation. The weight of the lungs was found to increase from 2gms to 30gms and the results were tabulated and compared with the previous results. The oblique fissure in both the lungs did not show any variation whereas the horizontal fissure had variations. Out of 50 specimens in the age group of 10 weeks to 39 weeks of gestation the horizontal fissure was incomplete in 35 fetuses out of which 16 fetuses were in age group of 10-20 weeks, 17 fetuses were in age group of 21-30 weeks and 2 fetuses were in age group of 31-39 weeks of gestation. The bronchopulmonary segments were studied in the left lung of fetuses in age group of 20 to 39 weeks of gestation and results were tabulated. Group I fetuses of 20 to 25 weeks of gestation had ill-defined segmental bronchi. Group II fetuses of 26 to 30 weeks of gestation had nine bronchopulmonary segments in 6 fetuses and ten bronchopulmonary segments in 5 fetuses. Group III fetuses of 31 to 35 weeks of gestation were found to have nine bronchopulmonary segments in 3 fetuses and ten bronchopulmonary segments in 4 fetuses. Group IV fetuses of 36 to 39 weeks of gestation had nine bronchopulmonary segments in 1 fetus and ten bronchopulmonary segments in 3 fetuses. The histology of the branching pattern in the lower lobe of the right lung was seen. The tissues were processed and stained with Haemotoxylin and Eosin method. The microscopic structure was studied in the lower lobe of right lung in the fetuses. The histological picture showed that the bronchial tubules were lined by simple cuboidal epithelium till 20th week of gestation and the bronchi were lined by pseudostratified ciliated columnar epithelium from 12 weeks of gestation. The terminal bronchioles were lined by columnar epithelium and respiratory bronchioles were lined by simple cuboidal epithelium. The cartilage plates around the bronchial wall, cilia in the bronchial epithelium and blood vessels started to appear at 12th week of gestation. The bronchial gland buds appeared at 15th week of gestation and mucous acini appeared at 21st week of gestation. The respiratory epithelium started to differentiate at 24th week of gestation and well differentiated into type I and type II pneumocytes at 34th and 39th week of gestation. CONCLUSION: The study was conducted in the fetal lungs to find out the branching pattern and appearance of the cartilage and the type II pneumocytes by microscopic study. In this modern era the knowledge of variation in the bronchial branching pattern is helpful for Anatomists in teaching purposes. Pulmonologists should have an idea about the variations in the bronchial branching pattern while performing the bronchoscopy and in treating the lung abscess or tuberculosis and lung cancer patients. The knowledge about the variations in the branching pattern is very important for the cardiothoracic surgeons while performing the lobectomies for lung abscess and in cancer condition. The knowledge about the developmental stages of the lung is most useful for the Pediatricians since failure of development of the cartilage leads to pulmonary hypoplasia and congenital emphysema. Obstetrician and gynecologists should have an idea about the developmental stages of the lung and the time of appearance of type II pneumocytes while performing normal and caesarian section deliveries. Since type II pneumocytes is responsible for the production of surfactant and this is helpful in finding the viability period of the fetus. Inadequate production of surfactant leads to respiratory distress syndrome in the fetus