Ultrastructure of the tracheobronchial epithelium of the normal and formaldehyde-exposed guinea-pig

Thirty adult male guineca pigs were used in this study, fifteen taken as control, while the other fifteen were exposed to formaldehyde.The tracheobronchial epithelium of all animals were examined by means of light and electron microscopy. The tracheobronchial epithelium of the control animals was found to consist of ciliated, goblet, basal and intermediate cells. The general structure of the epithelium is suggested to provide a barrier restricting the transfer of exogenous material from the airway lumen to the blood stream. Moreover, the actively motile cilia of the ciliated cells are responsible for transport of mucus with included foreign materials to the throat where the mucus normally swallowed. The goblet cells continuously secrete mucus which formed a physical barrier between the inhaled pollutants and underlying epithelium. The results of this work suggest that, both motile cilia and secretion of correct amount of mucus with suitable vesicoelasticity are responsible for maintenance of mucociliaryy clearance. Also the intermediate cells were observed to be differentiated into goblet cells. Following formaldehyde exposure, profound general and special epithelial and submucosal changes, ranging from moderate to severe were observed within the tracheobronchial epithelium.Early after short periods of formaldehyde exposure, the structural changes in the bronchial epithelium were observed to be less severe than that of the tracheal epithelium. However, later on, with prolongation of the period of formaldehyde exposure, both trachea and bronchi were severely affected. The general epithelial changes included, 1] ulceration of the tracheobronchial epithelium which is emphasized to expose and sensitize the airway receptors to inhaled irritants which are responsible for the pathogenesis of occupational asthma. 2] proliferative changes in the form of simple hyperplasia, basal and goblet cell hyperplasia and squamous metaplasia have occurred and suggested the possibility of formaldehyde carcinogenicity 3] thickening of the basement membrane which is considered to be a protective mechanism against inhaled formaldehyde. On the other hand, the special epithelial changes were evidenced by the appearance of a great number of ciliary abnormalities and apocrine, massive mucus secretion of the goblet cells with subsequent impairment of the mucociliary clearance. Both fibrosis and airway obstruction are considered to be the latest sequlae of long term injury produced by formaldehyde exposure as indicated by the appearance of fibroblasts and smooth muscle fibers within the submucosa of tracheobronchial epithelium

Ultrastructure of the tracheobronchial epithelium of the normal and formaldehyde-exposed guinea-pig

Thirty adult male guinea pigs were used in this study, fifteen were taken as control, while the other fifteen were exposed to formaldehyde.The tracheobronchial epithelium of all animals were examined by means of light and electron microscopy. The tracheobronchial epithelium of the control animals was found to consist of ciliated, goblet, basal and intermediate cells. The general structure of the epithelium is suggested to provide a barrier restricting the transfer of exogenous material from the airway lumen to the blood stream. Moreover, the actively motile cilia of the ciliated cells are responsible for transport of mucus with included foreign materials to the throat where the mucus normally swallowed. The goblet cells continuously secrete mucus which formed a physical barrier between the inhaled pollutants and underlying epithelium. The results of this work suggested that, both motile cilia and secretion of correct amount of mucus with suitable vesicoelasticity are responsible for maintenance of mucociliary clearance. Also the intermediate cells were observed to be differentiated into goblet cells. Following formaldehyde exposure, profound general and special epithelial and submucosal changes, ranging from moderate to severe were observed within the tracheobronchial epithelium. Early after short periods of formaldehyde exposure, the structural changes in the bronchial epithelium were observed to be less severe than that of the tracheal epithelium. However, later on, with prolongation of the period of formaldehyde exposure, both trachea and bronchi were severely affected. The general epithelial changes included, 1] ulceration of the tracheobronchial epithelium which is emphasized to expose and sensitize the airway receptors to inhaled irritants which are responsible for the pathogenesis of occupational asthma. 2] proliferative changes in the form of simple hyperplasia, basal and goblet cell hyperplasia and squamous metaplasia have occurred and suggested the possibility of formaldehyde carcinogenicity 3] thickening of the basement membrane which is considered to be a protective mechanism against inhaled formaldehyde. On the other hand, the special epithelial changes were evidenced by the appearance of a great number of ciliary abnormalities and apocrine massive mucus secretion of the goblet cells with subsequent impairment of the mucociliary clearance. Both fibrosis and airway obstruction are considered to be the latest sequlae of long term injury produced by formaldehyde exposure as indicated by the appearance of fibroblasts and smooth muscle fibers within the submucosa of tracheobronchial epithelium

development of the retina and optic stak in rat embryos

This work was done to study the prenatal development of the retina and optic chiasma in albino rat embryos in an attempt to provide the mechanism of optic axonal guidance and to elucidate the relation between the cytodifferentation of the retina and its central nervous connection. Thirty rat embryos in age from 12 days to 21 days [full term newborn], were used in this study. The results of the present work indicate that the projection of the outgrowing axons araised from the early developing ganglion cells and extend in the direction of the optic dise has occurred through the extracellular spaces, which formed inside the superficial portion of the retina during the early period of generation. Moreover, the findings of this work suggest that the origin of the retinal macroglial cells [astrocytes] is the neuroepithelial cells of the optic stalk that reach the retina through its blood vessels. Theses cells together with the developing glial cells derived from the floor of dienecphalon are emphasized to act as candidates for guidance of the nerve axons within the retina, optic stalk and optic stalk prior to penetration of the axons are postulated to minimize the resistance of axonal advance through the stalk providing a potential path for the growing axons to reach the diencephalons. This was followed by concomitant maturation of the ganglion cells and differentiation of the inner plexiform layer of retina during the late stages of gestation

Early development of the spiral ganglion and organ of corti in albino rat embryos

This work was done to study the early development of the spiral ganglion and the cochlear duct in albino rat embryos in an attempt to clarify the relation between the cytodifferentiation of the organ of Corti and its innervation. Thirty rat embryos ranging in age from 12.5 days to full-term, were used in this study. The results of this work suggest a notion of a double origin of the spiral ganglion from both neural crest and otocyst and also support the tonotopic organization of the central auditory pathway explaining the tonotopic processing of the complex sounds. Moreover, the neural crest throughout the prenatal period continues to contribute schwannoblasts to the spiral ganglion and their peripheral and central nerve projections initiating the early myelination of the auditory pathway. On the other hand, the results of this work indicate that the whole cochlear duct is developed from a single mitotic center located on the anteromedial wall of otocyst. The rapid growth and coiling of the cochlear duct occurs at the early stages of development as a result of the early innervation of the anteromedial wall of otocyst through the mitotic center. The subsequent innervation of the presumptive sensory cells within the medial wall of the completely coiled cochlear duct usually associated with the early appearance of undifferentiated multilayered organ of Corti. In later stages of development, the maturation of the spiral ganglion and organ of Corti seems to follow a sequential and interdependent process of differentiation related to: 1] stratification of the peripheral and central nerve projections; 2] mesenchymal clearance of perilymphatic spaces and formation of the scala vestibuli and scala tympani; 3] maturation of Reissner's membrane, stria vascularis and spiral lamina. Concerning formation of the tectorial membrane, the results of this work point out to the involvement of the cells of the great epithelial ridge in secretion of the main portion of the tectorial membrane. However, the cells of the small epithelial ridge represent a minor source for secretion of the tectorial membrane at its early stages of development

Ultrastructural study on functional activity of thyroid follicular cells in rats

The thyroid gland of ten albino rats aged 4 weeks [with high blood level of thyroid stimulating hormone] were studied ultrastructurally in an attempt to elucidate the functional activity of the gland and the pathway of thyroid secretion. The ultrastructural features of the thyroid follicular cells showed two patterns of activity indicative of synthesis and secretion. The main part of thyroglobulin synthesis was localised in ribosomes, transported to cisternae of endoplasmic reticulum, then migrated to the Golgi zone and came out of this zone in small membrane-bound vesicles to be released into the colloidal lumen. Based on the observations of this work, it was possible to recognize two pathways of of hormone release within the active processing and secretory cells the major pathway includes the formation of colloid droplets from the follicular lumen, this is followed by intracellular digestion of colloid by lysosomes and subsequent release of thyroid hormone; the other minor pathway of the secretion takes place within the follicular cells and both hormone synthesis and iodine-protein-binding are intracellular processes involving formation of small vesicles within the Golgi apparatus. The results of this work point out to the involvement of the apical microvilli and the specialization of the basal plasma membrane in concentration of iodide. In conclusion, two stages in the secretory cycle of thyroid follicular cells have been recognized. The synthesizing cell represents the first stage, where the precursors of the thyroid hormone were formed while the active processing and secretory cell represented the second stage, where packing and different secretory pathways were established