Histology of Respiratory System

Histology of Respiratory System Respiratory system   Conducting Portion Respiratory Portion Cell types found in “Respiratory epithelium” Ciliated columnar cells – move Mucus 1. 1. Immotile cilia syndrome Goblet cells – secrete mucus 3. Basal cells (stem cells) – replace damaged cells 4. Brush cells – sensory receptor cells 5. Small granule cells – enteroendocrine cells * Clara cells (trachea and bronchi) – protein Secreting cells, secrete surfactant 2. Figure 17–2. Photomicrograph illustrating the main components of the respiratory epithelium. Pararosaniline– toluidine blue (PT) stain. High magnification. Figure 17–3. Electron micrograph of ciliated columnar cells of the respiratory epithelium, showing the ciliary microtubules in transverse and oblique section. In the cell apex are the U-shaped basal bodies that serve as the source of, and anchoring sites for, the ciliary axonemes. The local accumulation of mitochondria is related to energy production for ciliary movement. Note the junctional complex. x9200. Figure 17–4. Scanning electron micrographs of the surface of respiratory mucosa. Top: Most of the surface is covered with cilia. G, goblet cells. x2500. Bottom: Subsurface accumulations of mucus are evident in the goblet cells (thin arrows). Thick arrowheads indicate brush cells. x3000. (Reproduced, with permission, from Andrews P: A scanning electron microscopic study of the extrapulmonary respiratory tract. Am J Anat 1974;139:421.) Nasal cavities  VESTIBULE or Nostril    Respiratory Segment     Stratified squamous non-cornified Sheet epithelium ”Respiratory Epithelium” Swelling bodies Arcading branches Olfactory Segment  Olfactory Epithelium Olfactory mucosa 1. Sustentacular or supporting cells 1. Olfactory cells 2. Basal cells Trachea  Mucosa    Submucosa     Loose to moderately densefect, Denser than lamina propria, May contain compound tubuloacinar glands “Muscularis”externa     “Respiratory” epithelium Lamina propria of loose FECT Hyaline cartilages (horseshoe-shaped “rings”) Smooth muscle across open ends of cartilages Moderately dense FECT connects adjacent rings Adventitia  Loose FECT Trachea aFigure 17–6. Section of trachea showing the respiratory epithelium with goblet cells and columnar ciliated cells. Also shown are serous glands in the lamina propria and hyaline cartilage. The mucous fluid produced by the goblet cells and by the glands forms a layer that permits the ciliary movement to propel foreign particles out of the respiratory system. PT stain. Medium magnification. Figure 17–8. Section of a bronchus wall showing the respiratory epithelium with goblet cells and columnar ciliated cells. The connective tissue of the lamina propria contains serous glands and smooth muscle (SM). In the lower half of the photomicrograph is a large piece of hyaline cartilage. PT stain. Medium magnification. Bronchus Figure 17–7. Structure of a bronchus. Smooth muscle is present in the entire bronchiolar tree, including the respiratory bronchiole. Contraction of this muscle induces folding of the mucosa. The elastic fibers in the bronchus continue into the bronchiole. The lower portion of the drawing represents a region with its connective tissue removed to show the presence of elastic fibers and smooth muscle. The adventitia is not shown. Bronchus (very similar to Trachea)  Mucosa    Submucosa     Loose to moderately dense FECT, denser than lamina propria, may contain compound tubuloacinar glands “Muscularis”externa     “Respiratory” epithelium Lamina propria of loose FECT Hyaline cartilages (horseshoe-shaped “rings”) Smooth muscle across open ends of cartilages Moderately dense FECT connects adjacent rings Adventitia  Loose FECT Large Bronchus Figure 17–9. Large bronchus. Note the distinct layer of smooth muscle that influences the flux of air in the respiratory system. PT stain. Medium magnification. Organization of lung Bronchioles Cell types of luminal epithelium of bronchioles       Ciliated cells Basal cells Goblet cells Brush cells Small granule cells(neuroepithelial) Clara cells Bronchioles aFigure 17–10. Section of a bronchus wall with bronchus-associated lymphoid tissue (BALT), a component of the diffuse mucosa-associated lymphoid tissue (MALT), whose distribution and functions are described in Chapter 14. PT stain. Medium magnification. aFigure 17–11. The same section as in Figure 17–10 but at higher magnification. The respiratory epithelium and its cilia are more evident. The lower part of the figure shows an activated region (germinal center) with light-stained areas, most with antigen-presenting macrophages. PT stain. High magnification. aFigure 17–12. Clara cells in the epithelium of a terminal bronchiole. These cells show secretory granules and a bulging apical cytoplasm. PT stain. High magnification. Figure 17–13. Photomicrograph of a section from the wall of a terminal bronchiole. Note that no cartilage is present, but there is an incomplete ring of smooth muscle. PT stain. Low magnification. Figure 17–14. Section of a terminal bronchiole with a small portion of a respiratory bronchiole continuous with an alveolar duct and many alveoli. PT stain. Low magnification. aFigure 17–15. Photomicrograph of a thick section of lung showing a terminal bronchiole dividing into 2 respiratory bronchioles, in which alveoli appear. The spongelike appearance of the lung is due to the abundance of alveoli and alveolar sacs. H&E stain. Low magnification. Figure 17–16. Diagram of a portion of the bronchial tree. Note that the smooth muscle in the alveolar duct disappears in the alveoli. (Redrawn from Baltisberger.) Figure 17–17. Bird’s-eye view of a lung section showing branching of bronchioles with different sizes of bronchioles (1, 2, 3), large blood vessels, and alveoli. PT stain. Low magnification. Figure 17–18. Transition of a terminal bronchiole into an alveolar duct (arrow). Note the Clara cells (arrowheads). PT stain. Medium magnification. Alveoli (air spaces) Figure 17–19. Three-dimensional schematic diagram of pulmonary alveoli showing the structure of the interalveolar septum. Note the capillaries, connective tissue, and macrophages. These cells can also be seen in—or passing into—the alveolar lumen. Alveolar pores are numerous. Type II cells are identified by their abundant apical microvilli. The blood-air barrier Figure 17–20. Portion of the interalveolar septum showing the blood-air barrier. To reach the erythrocyte, O2 traverses the surface lining, the alveolar epithelium cytoplasm, and the plasma. In some locations, there is loose interstitial tissue between the epithelium and the endothelium. (Modified and reproduced, with permission, from Ganong WF: Review of Medical Physiology, 8th ed. Lange, 1977.) Figure 17–21. Electron micrograph of the interalveolar septum. Note the capillary lumen, alveolar spaces, alveolar type I epithelial cells, fused basal laminae, and a fibroblast. x30,000. (Courtesy of MC Williams.) Cell types found in alveolar epithelium 1. 2. 3. 4. Type I Pneumocytes [gas exchange, pinocytosis] Type II Pneumocytes [secrete surfactant (mix of proteins and lipids)] Brush Cells [sensory receptors] Dust cells (Pulmonary Macrophages) [phagocytosis] Figure 17–22. Alveoli and interalveolar septum showing blood capillaries and epithelial cells type I and type II. PT stain. Medium magnification. Figure 17–23. Section of a lung fixed by intra-alveolar injection of fixative. Observe in the interalveolar septum 3laminar structures (arrowheads) constituted by a central basement membrane and 2 very thin cytoplasmic layers. These layers are formed by the cytoplasm of epithelial cell type I and the cytoplasm of capillary endothelial cells. PT stain. High magnification. Figure 17–24. Cryofracture preparation showing an occluding junction between 2 type I epithelial cells of the alveolar lining. x25,000. (Reproduced, with permission, from Schneeberger EE: Lung Liquids. Ciba Foundation Symposium no. 38. Elsevier/North-Holland, 1976.) Secretion of surfactant by a type II cell Figure 17–25. Secretion of surfactant by a type II cell. Surfactant is a protein-lipid complex synthesized in the rough endoplasmic reticulum and Golgi complex and stored in the lamellar bodies. It is continuously secreted by means of exocytosis (arrows) and forms an overlying monomolecular film of lipid covering an underlying aqueous hypophase. Occluding junctions around the margins of the epithelial cells prevent leakage of tissue fluid into the alveolar lumen. Figure 17–26. Electron micrograph of a type II cell protruding into the alveolar lumen. Arrows indicate lamellar bodies containing newly synthesized pulmonary surfactant. RER, rough endoplasmic reticulum; G, Golgi complex; RF, reticular fibers. Note the microvilli of the type II cell and the junctional complexes (JC) with the type I epithelial cell. x17,000. (Courtesy of MC Williams.) Figure 17–27. Blood and lymph circulation in a pulmonary lobule. Both vessels and bronchi are enlarged out of proportion in this drawing. In the interlobular septum, only one vein (on the left) and one lymphatic vessel (on the right) are shown, although both actually coexist in both regions. At the lower left, an enlargement of the pleura shows its mesothelial lining. (Modified and reproduced, with permission, from Ham AW: Histology, 6th ed. Lippincott, 1969.)