Bronchiole
 | This article includes a list of generalreferences,butit lacks sufficient correspondinginline citations.(May 2015) |
| Bronchiole | |
|---|---|
 Diagram of thealveoliwith both cross-section and external view. | |
| Details | |
| System | Respiratory system |
| Identifiers | |
| MeSH | D055745 |
| TA98 | A06.5.02.026 |
| TA2 | 3282 |
| TH | H3.05.02.0.00005 |
| FMA | 7410 |
| Anatomical terminology | |
Thebronchiolesorbronchioli(pronouncedbron-kee-oh-lee) are the smaller branches of thebronchial airwaysin thelower respiratory tract.They include the terminal bronchioles, and finally the respiratory bronchioles that mark the start of therespiratory zonedelivering air to thegas exchanging unitsof thealveoli.The bronchioles no longer contain the cartilage that is found in the bronchi, or glands in theirsubmucosa.[1]
Structure
[edit]
Thepulmonary lobuleis the portion of thelungventilated by one bronchiole. Bronchioles are approximately 1 mm or less in diameter and their walls consist ofciliatedcuboidalepitheliumand a layer ofsmooth muscle. Bronchioles divide into even smaller bronchioles, calledterminal,which are 0.5 mm or less in diameter. Terminal bronchioles in turn divide into smaller respiratory bronchioles which divide intoalveolar ducts.Terminal bronchioles mark the end of the conducting division of air flow in therespiratory systemwhile respiratory bronchioles are the beginning of the respiratory division wheregas exchangetakes place.
The diameter of the bronchioles plays an important role in air flow. The bronchioles change diameter to either increase or reduce air flow. An increase in diameter is calledbronchodilationand is stimulated by eitherepinephrineorsympathetic nervesto increase air flow. A decrease in diameter is calledbronchoconstriction,which is the tightening of the smooth muscle surrounding the bronchi and bronchioles due to and stimulated byhistamine,parasympathetic nerves,cold air, chemical irritants, excess mucus production, viral infections, and other factors to decrease air flow. Bronchoconstriction can result in clinical symptoms such as wheezing, chest tightness, and dyspnea, which are common features of asthma, chronic obstructive pulmonary disease (COPD), and chronic bronchitis.[2]
Bronchioles
[edit]
Thetracheadivides into the left mainbronchuswhich supplies the left lung, and the right main bronchus which supplies the right lung. As they enter the lungs these primary bronchi branch into secondary bronchi known aslobar bronchiwhich supply each lobe of the lung. These in turn give rise to tertiary bronchi (tertiarymeaning "third" ), known assegmental bronchiwhich supply eachbronchopulmonary segment.[1]The segmentary bronchi subdivide into fourth order, fifth order and sixth order segmental bronchi before dividing into the bronchioles. The bronchioles are histologically distinct from the bronchi in that their walls do not havehyaline cartilageand they haveclub cellsin their epithelial lining. Theepitheliumof the bronchioles starts as asimple ciliated columnar epitheliumand changes tosimple ciliated cuboidal epitheliumas the bronchioles decreases in size. The diameter of the bronchioles is often said to be less than 1 mm, though this value can range from 5 mm to 0.3 mm. As stated, these bronchioles do not have hyaline cartilage to maintain their patency. Instead, they rely onelastic fibersattached to the surroundinglungtissue for support. The inner lining (lamina propria) of these bronchioles is thin with no glands present, and is surrounded by a layer ofsmooth muscle.As the bronchioles get smaller they divide into terminal bronchioles. Each bronchiole divides into between 50 and 80 terminal bronchioles.[3]These bronchioles mark the end of theconducting zone,which covers the first division through the sixteenth division of therespiratory tract.Alveolionly become present when the conducting zone changes to therespiratory zone,from the sixteenth through the twenty-third division of the tract.
Terminal bronchioles
[edit]The terminal bronchioles are the most distal segment of the conducting zone. They branch off the lesser bronchioles. Each of the terminal bronchioles divides to form respiratory bronchioles which contain a small number of alveoli. Terminal bronchioles are lined withsimple ciliated cuboidal epitheliumcontainingclub cells.Club cells are non-ciliated, rounded protein-secreting cells. Their secretions are a non-sticky, proteinaceous compound to maintain the airway in the smallest bronchioles. The secretion, calledpulmonary surfactant,reducessurface tension,allowing for bronchioles to expand during inspiration and keeping the bronchioles from collapsing during expiration. Club cells are astem cellof therespiratory system,and also produceenzymesthat detoxify substances dissolved in the respiratory fluid.
Respiratory bronchioles
[edit]The respiratory bronchioles are the narrowest airways of the lungs, 0.5 mm across.[4]Thebronchidivide many times before evolving into the bronchioles. The respiratory bronchioles deliver air to the exchange surfaces of the lungs.[5] They are interrupted byalveoliwhich are thin walledevaginations.Alveolar ductsare side branches of the respiratory bronchioles. The respiratory bronchioles are lined by ciliated columnar epithelium along with some non-ciliated cells calledclub cells.[6]
Clinical significance
[edit]Bronchospasm,a potentially life-threatening situation, occurs when the smooth muscular tissue of the bronchioles constricts, severely narrowing their diameter. The most common cause of this is asthma. Bronchospasm is commonly treated byoxygen therapyandbronchodilatorssuch asalbuterol.
Diseases of the bronchioles includeasthma,bronchiolitis obliterans,respiratory syncytial virusinfections, andinfluenza.
Inflammation
[edit]The medical condition of inflammation of the bronchioles is termedbronchiolitis.[7]
Additional images
[edit]-
Cross sectional cut of primary bronchiole -
- Trachea
- Primarybronchus
- Lobar bronchus
- Segmental bronchus
- Bronchiole
- Alveolar duct
- Alveolus
References
[edit]- ^abTortora GJ (2010).Principles of anatomy and physiology(12th ed.). Hoboken, NJ: John Wiley & Sons. pp. 883–888.ISBN9780470233474.
- ^Bacsi A, Pan L, Ba X, Boldogh I (February 2016)."Pathophysiology of bronchoconstriction: role of oxidatively damaged DNA repair".Current Opinion in Allergy and Clinical Immunology.16(1): 59–67.doi:10.1097/ACI.0000000000000232.PMC4940044.PMID26694039.
- ^Saladin K (2011).Human anatomy(3rd ed.). McGraw-Hill. pp. 640–641.ISBN9780071222075.
- ^Merck Manual of Medical Information(Home ed.). Whitehouse Station, N.J.: Merck Research Laboratories. 1997.ISBN978-0-911910-87-2.
- ^Martini FH, Timmons MJ, Tallitsch RB.Human Anatomy(6th ed.). Benjamin Cummings. p. 643.ISBN978-0-321-49804-5.
- ^Paxton, Steve; Peckham, Michelle; Knibbs, Adele (2003)."Respiratory: Trachea, bronchioles and bronchi".University of Leeds.
- ^Friedman JN, Rieder MJ, Walton JM (November 2014)."Bronchiolitis: Recommendations for diagnosis, monitoring and management of children one to 24 months of age".Paediatrics & Child Health.19(9): 485–498.doi:10.1093/pch/19.9.485.PMC4235450.PMID25414585.
Further reading
[edit]- Saladin, Kenneth S. Anatomy & Physiology: the Unity of Form and Function. New York, NY: McGraw-Hill, 2007.
- Dudek, Ronald W.High-Yield Histology,3rd ed. (2004).ISBN0-7817-4763-5
- Gartner, Leslie P. and James L. Hiatt.Color Atlas of Histology,3rd ed. (2000).ISBN0-7817-3509-2
- Gartner, Leslie P. and James L. Hiatt.Color Textbook of Histology(2001).ISBN0-7216-8806-3
External links
[edit]- Histology image: 13606loa– Histology Learning System at Boston University
- Histology image: 13607loa– Histology Learning System at Boston University
- Diagram at davidson.edu
- Histology at umdnj.edu
