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Sunday, July 27, 2008

Histology of Trachea

 Image taken from www.lab.anhb.uwa.edu.au
  • After inhaled air has passed through the nose, pharynx, and larynx, it enters the trachea. 
  • The trachea is a thick-walled tube, some 12 cm in length, that directs air down toward the pair of primary bronchi that enter the lung. 
  • The trachea's inner surface, facing the lumen, is lined by a pseudostratified columnar epithelium  that contains ciliated cells, goblet cells, and Basal Cells. 
  • The tracheal epithelium  lies atop a highly elastic lamina propria, which grades into the submucosa. 
  • The well-developed submucosa contains conspicuous rings of hyaline cartilage that keep the trachea open when the neck is bent or turned. 
  • The cartilage is covered by a tough perichondrium, which, in the outer region of the wall, is covered by the adventitia, a sheath of loose connective tissue that envelops the outer surface of the trachea. 
  • This spatial arrangement of component tissues - epithelium, lamina propria, submucosa, and adventitia - is common to many of the body's interior tubular systems. 
  Image taken from www.lab.anhb.uwa.edu.au
  • The epithelium and lamina propria are shown in greater detail in above image.
  • The goblet cells, as the name suggests, have a goblet-shaped cytoplasm filled with mucus droplets that displace the nucleus and bio synthetic machinery toward the basal pole of the cell. 
  • The ciliated cells  appear much darker and have numerous motile cilia projecting from the cell surface. Taken together, these two cell types generate the mucociliary blanket that protects the inner tracheal surface. 
  • The goblet cells, along with large submucosal glands, produce and secrete the mucus; the cilia move mucus toward the mouth. In this way, foreign materials that enter the respiratory system are entrapped by the sticky mucus and are rapidly moved toward the throat to be swallowed or expectorated. 
  • At the bottom of the epithelium are the basal cells, stem cells that replace worn-out ciliated and goblet cells.

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