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Respiratory epithelium

January 01, 1970

Respiratory epithelium, or airway epithelium,[1] is a type of ciliated columnar epithelium found lining most of the respiratory tract as respiratory mucosa,[2] where it serves to moisten and protect the airways. It is not present in the vocal cords of the larynx, or the oropharynx and laryngopharynx, where instead the epithelium is 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.

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
[edit on Wikidata]

Structure edit

 
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 ciliated pseudostratified columnar epithelium.[4] This designation is due to the arrangement of the multiple cell types composing the respiratory epithelium. While all cells make contact with the basement membrane and are, therefore, a single layer of cells, their nuclei are not aligned in the same plane. Hence, it appears as though several layers of cells are present and the epithelium is called pseudostratified (falsely layered). The respiratory mucosa transitions to simple ciliated cuboidal epithelium and finally to simple squamous epithelium in the alveolar ducts and alveoli.[5]

Cells edit

The cells in the respiratory epithelium are of five main types: a) ciliated cells, b) goblet cells, c) brush cells, d) airway basal cells, and e) small granule cells (NDES)[6] Goblet cells become increasingly fewer further down the respiratory tree until they are absent in the terminal bronchioles; club cells take over their role to some extent here.[7] Another important cell type is the pulmonary neuroendocrine cell. These are innervated cells that only make up around 0.5% of the respiratory epithelial cells.[7] The ciliated cells are 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 edit

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]

Goblet cells, so named because they are shaped like a wine goblet, are 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 edit

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 edit

  1. ^ Crystal, R (September 2008). "Airway epithelial cells: current concepts and challenges". Proc Am Thorac Soc. 15 (7): 772–777. doi:10.1513/pats.200805-041HR. PMC 5820806. PMID 18757316.
  2. ^ "Respiratory mucosa". meshb.nlm.nih.gov. Retrieved 26 July 2019.
  3. ^ Saladin, K (2012). Anatomy & physiology: the unity of form and function (6th ed.). McGraw-Hill. pp. 857–859. ISBN 9780073378251.
  4. ^ Mescher AL, "Chapter 17. The Respiratory System" (Chapter). Mescher AL: Junqueira's Basic Histology: Text & Atlas, 12e: . Archived from the original on 2013-06-03. Retrieved 2015-02-24..
  5. ^ "Bronchi, Bronchial Tree & Lungs". nih.gov. Retrieved 17 September 2019.
  6. ^ Mescher, Anthony L. (2018). Junqueira's basic histology: text and atlas (Fifteenth ed.). [New York]. p. 350. ISBN 978-1-26-002618-4.{{cite book}}: CS1 maint: location missing publisher (link)
  7. ^ a b Weinberger, Steven; Cockrill, Barbara; Mandel, Jess (2019). Principles of pulmonary medicine (Seventh ed.). Elsevier. p. 67. ISBN 9780323523714.
  8. ^ Yaghi, A; Dolovich, MB (11 November 2016). "Airway Epithelial Cell Cilia and Obstructive Lung Disease". Cells. 5 (4): 40. doi:10.3390/cells5040040. PMC 5187524. PMID 27845721.
  9. ^ a b Reid, L; Meyrick, B; Antony, VB; Chang, LY; Crapo, JD; Reynolds, HY (1 July 2005). "The mysterious pulmonary brush cell: a cell in search of a function". American Journal of Respiratory and Critical Care Medicine. 172 (1): 136–9. doi:10.1164/rccm.200502-203WS. PMC 2718446. PMID 15817800.
  10. ^ Hasleton, Philip (1996). Spencer's Pathology of the Lung. McGraw-Hill. pp. 10. ISBN 0071054480.
  11. ^ Perniss, Alexander; Lui, Shuya; Boonen, Brett; Zufall, Frank; Buffe, Bernd; Kummer, Wolfgang (2020-04-14). "Chemosensory Cell-Derived Acetylcholine Drives Tracheal Mucociliary Clearance in Response to Virulence-Associated Formyl Peptides". Cell Immunity. 52 (2): 683–699.e11. doi:10.1016/j.immuni.2020.03.005. PMID 32294408.
  12. ^ Hall, John (2011). Guyton and Hall Textbook of Medical Physiology. Saunders/Elsevier. p. 473. ISBN 9781416045748.
  13. ^ Stanke F The Contribution of the Airway Epithelial Cell to Host Defense. Mediators Inflamm. 2015;2015:463016. PMID 26185361 PMC 4491388
  14. ^ 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.
  15. ^ Hiemstra, PS; McCray PB, Jr; Bals, R (April 2015). "The innate immune function of airway epithelial cells in inflammatory lung disease". The European Respiratory Journal. 45 (4): 1150–62. doi:10.1183/09031936.00141514. PMC 4719567. PMID 25700381.
  16. ^ a b c Baker, EH; Baines, DL (February 2018). "Airway Glucose Homeostasis: A New Target in the Prevention and Treatment of Pulmonary Infection". Chest. 153 (2): 507–514. doi:10.1016/j.chest.2017.05.031. PMID 28610911. S2CID 13733461.
  17. ^ a b Garnett, JP; Baker, EH; Baines, DL (November 2012). "Sweet talk: insights into the nature and importance of glucose transport in lung epithelium". The European Respiratory Journal. 40 (5): 1269–76. doi:10.1183/09031936.00052612. PMID 22878875.
  18. ^ Global Initiative for Chronic Obstructive Lung Disease - GOLD (PDF). 2018. p. 15. Retrieved 10 November 2019.
  19. ^ Garg, A; Sui, P; Verheyden, JM; Young, LR; Sun, X (2019). "Consider the lung as a sensory organ: A tip from pulmonary neuroendocrine cells". Current Topics in Developmental Biology. 132: 67–89. doi:10.1016/bs.ctdb.2018.12.002. ISBN 9780128104897. PMID 30797518. S2CID 73489416.

Additional images edit

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

External links edit

January 01, 1970
respiratory, epithelium, airway, epithelium, type, ciliated, columnar, epithelium, found, lining, most, respiratory, tract, respiratory, mucosa, where, serves, moisten, protect, airways, present, vocal, cords, larynx, oropharynx, laryngopharynx, where, instead. Respiratory epithelium or airway epithelium 1 is a type of ciliated columnar epithelium found lining most of the respiratory tract as respiratory mucosa 2 where it serves to moisten and protect the airways It is not present in the vocal cords of the larynx or the oropharynx and laryngopharynx where instead the epithelium is 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 Respiratory epitheliumIllustration depicting the respiratory epithelium Basal cells labelled as stem cells DetailsSystemRespiratory systemIdentifiersMeSHD020545THH3 05 00 0 00003Anatomical terms of microanatomy edit on Wikidata Contents 1 Structure 1 1 Cells 2 Function 3 Clinical significance 4 References 5 Additional images 6 External linksStructure edit nbsp Pseudostratified columnar epithelium animated image highlights the epithelial cells goblet cells then underlying connective tissue nbsp 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 ciliated pseudostratified columnar epithelium 4 This designation is due to the arrangement of the multiple cell types composing the respiratory epithelium While all cells make contact with the basement membrane and are therefore a single layer of cells their nuclei are not aligned in the same plane Hence it appears as though several layers of cells are present and the epithelium is called pseudostratified falsely layered The respiratory mucosa transitions to simple ciliated cuboidal epithelium and finally to simple squamous epithelium in the alveolar ducts and alveoli 5 Cells edit The cells in the respiratory epithelium are of five main types a ciliated cells b goblet cells c brush cells d airway basal cells and e small granule cells NDES 6 Goblet cells become increasingly fewer further down the respiratory tree until they are absent in the terminal bronchioles club cells take over their role to some extent here 7 Another important cell type is the pulmonary neuroendocrine cell These are innervated cells that only make up around 0 5 of the respiratory epithelial cells 7 The ciliated cells are 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 editThe 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 Goblet cells so named because they are shaped like a wine goblet are 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 editLong 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 edit Crystal R September 2008 Airway epithelial cells current concepts and challenges Proc Am Thorac Soc 15 7 772 777 doi 10 1513 pats 200805 041HR PMC 5820806 PMID 18757316 Respiratory mucosa meshb nlm nih gov Retrieved 26 July 2019 Saladin K 2012 Anatomy amp physiology the unity of form and function 6th ed McGraw Hill pp 857 859 ISBN 9780073378251 Mescher AL Chapter 17 The Respiratory System Chapter Mescher AL Junqueira s Basic Histology Text amp Atlas 12e AccessMedicine the Respiratory System Introduction Archived from the original on 2013 06 03 Retrieved 2015 02 24 Bronchi Bronchial Tree amp Lungs nih gov Retrieved 17 September 2019 Mescher Anthony L 2018 Junqueira s basic histology text and atlas Fifteenth ed New York p 350 ISBN 978 1 26 002618 4 a href Template Cite book html title Template Cite book cite book a CS1 maint location missing publisher link a b Weinberger Steven Cockrill Barbara Mandel Jess 2019 Principles of pulmonary medicine Seventh ed Elsevier p 67 ISBN 9780323523714 Yaghi A Dolovich MB 11 November 2016 Airway Epithelial Cell Cilia and Obstructive Lung Disease Cells 5 4 40 doi 10 3390 cells5040040 PMC 5187524 PMID 27845721 a b Reid L Meyrick B Antony VB Chang LY Crapo JD Reynolds HY 1 July 2005 The mysterious pulmonary brush cell a cell in search of a function American Journal of Respiratory and Critical Care Medicine 172 1 136 9 doi 10 1164 rccm 200502 203WS PMC 2718446 PMID 15817800 Hasleton Philip 1996 Spencer s Pathology of the Lung McGraw Hill pp 10 ISBN 0071054480 Perniss Alexander Lui Shuya Boonen Brett Zufall Frank Buffe Bernd Kummer Wolfgang 2020 04 14 Chemosensory Cell Derived Acetylcholine Drives Tracheal Mucociliary Clearance in Response to Virulence Associated Formyl Peptides Cell Immunity 52 2 683 699 e11 doi 10 1016 j immuni 2020 03 005 PMID 32294408 Hall John 2011 Guyton and Hall Textbook of Medical Physiology Saunders Elsevier p 473 ISBN 9781416045748 Stanke F The Contribution of the Airway Epithelial Cell to Host Defense Mediators Inflamm 2015 2015 463016 PMID 26185361 PMC 4491388 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 Hiemstra PS McCray PB Jr Bals R April 2015 The innate immune function of airway epithelial cells in inflammatory lung disease The European Respiratory Journal 45 4 1150 62 doi 10 1183 09031936 00141514 PMC 4719567 PMID 25700381 a b c Baker EH Baines DL February 2018 Airway Glucose Homeostasis A New Target in the Prevention and Treatment of Pulmonary Infection Chest 153 2 507 514 doi 10 1016 j chest 2017 05 031 PMID 28610911 S2CID 13733461 a b Garnett JP Baker EH Baines DL November 2012 Sweet talk insights into the nature and importance of glucose transport in lung epithelium The European Respiratory Journal 40 5 1269 76 doi 10 1183 09031936 00052612 PMID 22878875 Global Initiative for Chronic Obstructive Lung Disease GOLD PDF 2018 p 15 Retrieved 10 November 2019 Garg A Sui P Verheyden JM Young LR Sun X 2019 Consider the lung as a sensory organ A tip from pulmonary neuroendocrine cells Current Topics in Developmental Biology 132 67 89 doi 10 1016 bs ctdb 2018 12 002 ISBN 9780128104897 PMID 30797518 S2CID 73489416 Additional images edit nbsp Cross section of pseudostratified columnar epithelium nbsp Second cross sectionExternal links edit Retrieved from https en wikipedia org w index php title Respiratory epithelium amp oldid 1215739669, wikipedia, wiki, book, books, library,

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