Respiratory epithelium

Source: Wikipedia, the free encyclopedia.
(Redirected from
Respiratory mucosa
)
Respiratory epithelium
Illustration depicting the respiratory epithelium. Basal cells labelled as stem cells.
Details
SystemRespiratory system
Identifiers
MeSHD020545
THH3.05.00.0.00003
Anatomical terms of microanatomy

Respiratory epithelium, or airway epithelium,

stratified squamous.[3] It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by the secretion of mucus and the action of mucociliary clearance
.

Structure

pseudostratified epithelium
Pseudostratified columnar epithelium, animated image highlights the epithelial cells, goblet cells, then underlying connective tissue
Cells of the respiratory epithelium. Basal cells shown in purple, ciliated cells shown in brown, goblet cells shown in green, and submucosal gland shown in blue.

The respiratory epithelium lining the upper respiratory airways is classified as

alveolar ducts and alveoli.[5]

Cells

The cells in the respiratory epithelium are of five main types: a)

columnar epithelial cells with specialized ciliary modifications. The ciliated cells make up between 50 and 80 per cent of the epithelium.[8]

Between the ciliated cells are numerous

microvilli, attached as tufts to brush cells sometimes referred to as pulmonary brush cells;[9] these are also known as the tuft cells of the gastrointestinal tract, or intestinal tuft cells,[10] although there is a difference between the two types: the brush cells lack the terminal web that lies under the microvilli of the tuft cells.[9] Although their function is not yet fully understood, it has been suggested that they exhibit a virulence associated clearance role, activating mucociliary clearance by releasing acetylcholine.[11]

Function

The respiratory epithelium functions to moisten and protect the airways. It acts as a physical barrier to pathogens, as well as their removal in the mechanism of mucociliary clearance.

The ciliated cells are the primary components in the mucociliary clearance mechanism. Each epithelial cell has around 200

cilia that beat constantly at a rate of between 10 and 20 times per second. The direction of their beat is targeted towards the pharynx, either upwards from the lower respiratory tract or downwards from the nasal structures.[12]

columnar epithelial cells that contain membrane-bound mucous granules and secrete mucus as part of the airway surface liquid (ASL), also known as the epithelial lining fluid, the composition of which is tightly regulated; the mucus helps maintain epithelial moisture and traps particulate material and pathogens moving through the airway. and determines how well mucociliary clearance works.[13][14]

The basal cells are small, nearly cuboidal that differentiate into the other cell types found within the epithelium. Basal cells respond to injury of the airway epithelium, migrating to cover a site denuded of differentiated epithelial cells, and subsequently differentiating to restore a healthy epithelial cell layer. The differentiated epithelial cells can also dedifferentiate into stem cells and contribute to the repairing of the barrier.[15]

Club cells carry out similar functions in the more distal airways.

Certain parts of the respiratory tract, such as the oropharynx, are also subject to the abrasive swallowing of food. To prevent the destruction of the epithelium in these areas, it changes to stratified squamous epithelium, which is better suited to the constant sloughing and abrasion. The squamous layer of the oropharynx is continuous with the esophagus.[citation needed]

The respiratory epithelium has a further role of immunity for the lungs - that of glucose homeostasis.[16] The glucose concentration in the airway surface liquid is held at a level of around 12 times lower than that of the blood sugar concentration.[16] The tight junctions act as a barrier that restricts the passage of glucose across the epithelium into the airway lumen. Some glucose passes through, where it diffuses into the airway surface liquid to be kept at its reduced level by pulmonary glucose transport, and metabolism.[17] However, airway inflammation decreases the effectiveness of the tight junctions making the barrier more permeable to glucose. Higher levels of glucose promote the proliferation of bacteria by providing glucose as a source for carbon for them.[16] Increased levels of glucose in the airway surface liquid is associated with respiratory diseases, and hyperglycemia.[17]

Clinical significance

Long-term irritation of the epithelial cells can cause the overproduction of mucus, known as

mucus hypersecretion. Mucus hypersecretion results in the productive cough of chronic bronchitis.[18]

Pulmonary neuroendocrine cells have been associated with a range of chronic lung disorders. They are also the originating cells of small-cell lung cancer.[19]

References

  1. PMID 18757316
    .
  2. ^ "Respiratory mucosa". meshb.nlm.nih.gov. Retrieved 26 July 2019.
  3. .
  4. ^ Mescher AL, "Chapter 17. The Respiratory System" (Chapter). Mescher AL: Junqueira's Basic Histology: Text & Atlas, 12e: "AccessMedicine | the Respiratory System: Introduction". Archived from the original on 2013-06-03. Retrieved 2015-02-24..
  5. ^ "Bronchi, Bronchial Tree & Lungs". nih.gov. Retrieved 17 September 2019.
  6. ISBN 978-1-26-002618-4.{{cite book}}: CS1 maint: location missing publisher (link
    )
  7. ^ .
  8. .
  9. ^ .
  10. .
  11. .
  12. .
  13. ^ U.S. EPA. Integrated Science Assessment for Oxides of Nitrogen – Health Criteria (2016 Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-15/068, 2016. Federal Register Notice Jan 28, 2016 Free download available at Report page at EPA website.
  14. PMID 25700381
    .
  15. ^ .
  16. ^ .
  17. ^ Global Initiative for Chronic Obstructive Lung Disease - GOLD (PDF). 2018. p. 15. Retrieved 10 November 2019.
  18. S2CID 73489416
    .

Additional images

  • Cross-section of pseudostratified columnar epithelium
    Cross-section of pseudostratified columnar epithelium
  • Second cross-section
    Second cross-section

External links