| Bronchus |
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Conducting passages.
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Front view of cartilages of larynx, trachea and bronchi.
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| Details |
| Latin |
Bronchus |
| System |
Respiratory system |
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Artery
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Bronchial artery |
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Vein
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Bronchial vein |
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Nerve
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Pulmonary branches of vagus nerve |
| Identifiers |
| Gray's |
p.1084 |
| MeSH |
A04.411.125 |
Dorlands
/Elsevier |
b_23/12198294 |
| TA |
A06.4.01.001 |
| FMA |
70774 |
| Anatomical terminology |
A bronchus, also known as a main or primary bronchus, is a passage of airway in the respiratory tract that conducts air into the lungs. There is a right bronchus and a left bronchus and these bronchi branch into smaller secondary and tertiary bronchi which branch into smaller tubes, known as bronchioles.[1] No gas exchange takes place in the bronchi.
Contents
- 1 Structure
- 1.1 Histology
- 1.2 Variation
- 2 Function
- 3 Clinical significance
- 3.1 Bronchitis
- 3.2 Aspiration
- 3.3 Asthma
- 4 Additional images
- 5 References
- 6 Sources
- 7 External links
Structure
The trachea (windpipe) divides into two main or primary bronchi, the left and the right, at the level of the sternal angle and of the fifth thoracic vertebra or up to two vertebrae higher or lower, depending on breathing, at the anatomical point the carina of trachea.
The right main bronchus is wider, shorter, and more vertical than the left main bronchus.[2]It enters the right lung at approximately the fifth thoracic vertebra. The right main bronchus subdivides into three secondary bronchi (also known as lobar bronchi), which deliver oxygen to the three lobes of the right lung—the superior, middle and inferior lobe. The azygos vein arches over it from behind; and the right pulmonary artery lies at first below and then in front of it. About 2 cm from its commencement it gives off a branch to the superior lobe of the right lung, which is also called the eparterial bronchus. Eparterial refers to its position above the right pulmonary artery. The right bronchus now passes below the artery, and is known as the hyparterial branch which divides into the two lobar bronchi to the middle and lower lobes.
The left main bronchus is smaller in caliber but longer than the right, being 5 cm long. It enters the root of the left lung opposite the sixth thoracic vertebra. It passes beneath the aortic arch, crosses in front of the esophagus, the thoracic duct, and the descending aorta, and has the left pulmonary artery lying at first above, and then in front of it. The left bronchus has no eparterial branch, and therefore it has been supposed by some that there is no upper lobe to the left lung, but that the so-called upper lobe corresponds to the middle lobe of the right lung. The left main bronchus divides into two secondary or lobar bronchi to deliver air to the two lobes of the left lung—the superior and the inferior lobe.
The secondary bronchi divide further into tertiary bronchi, (also known as segmental bronchi), each of which supplies a bronchopulmonary segment. A bronchopulmonary segment is a division of a lung separated from the rest of the lung by a septum of connective tissue. This property allows a bronchopulmonary segment to be surgically removed without affecting other segments. Initially, there are ten segments in each lung, but during development with the left lung having just two lobes, two pairs of segments fuse to give eight, four for each lobe. The tertiary bronchi divide into many smaller bronchioles which divide into terminal bronchioles, each of which then gives rise to several respiratory bronchioles, which go on to divide into two to eleven alveolar ducts. There are five or six alveolar sacs associated with each alveolar duct. The alveolus is the basic anatomical unit of gas exchange in the lung.
The main bronchi have relatively large lumens that are lined by respiratory epithelium. This cellular lining has cilia departing towards the mouth which removes dust and other small particles. There is a smooth muscle layer below the epithelium arranged as two ribbons of muscle that spiral in opposite directions. This smooth muscle layer contains seromucous glands, which secrete musus, in its wall. Hyaline cartilage is present in the bronchi, surrounding the smooth muscle layer. In the main bronchi, hyaline cartilage forms an incomplete ring, giving a "D"-shaped appearance, while in the smaller bronchi, hyaline cartilage is present in irregularly arranged plates and islands. These plates give structural support to the bronchi and keep the airway open.
Histology
Main article: Respiratory epithelium
Pseudostratified columnar ciliated epithelium - mag. x600
Cross section of secondary bronchus
The cartilage and mucous membrane of the primary bronchi are similar to those in the trachea. They are lined with respiratory epithelium, which is classified as ciliated pseudostratified columnar epithelium.[3] The epithelium in the main bronchi contains goblet cells, which are glandular, modified simple columnar epithelial cells that produce mucins, the main component of mucus. Mucus plays an important role in keeping the airways clear via the mucociliary escalator. As branching continues through the bronchial tree, the amount of hyaline cartilage in the walls decreases until it is absent in the bronchioles. As the cartilage decreases, the amount of smooth muscle increases. The mucous membrane also undergoes a transition from ciliated pseudostratified columnar epithelium to simple cuboidal epithelium to simple squamous epithelium.[3]
Variation
In 0.1 to 5% of people there is a right superior lobe bronchus arising from the main stem bronchus prior to the carina. This is known as a tracheal bronchus, and seen as an anatomical variation. It can have multiple variations and, although usually asymptomatic, it can be the root cause of pulmonary disease such as a recurrent infection. In such cases resection is often curative[4] [5]
Function
See also: Respiratory tree
The alveolar ducts and alveoli consist primarily of simple squamous epithelium, which permits rapid diffusion of oxygen and carbon dioxide. Exchange of gases between the air in the lungs and the blood in the capillaries occurs across the walls of the alveolar ducts and alveoli.
Clinical significance
Bronchitis
Main article: Bronchitis
Bronchitis is defined as inflammation of the bronchi, which can either be acute or chronic. Acute bronchitis is usually caused by viral or bacterial infections. Most sufferers of chronic bronchitis also suffer from chronic obstructive pulmonary disease (COPD), and is usually associated with smoking or long-term exposure to irritants.
Aspiration
While the left mainstem bronchus departs from the trachea at an angle, the right mainstem bronchus is almost a vertical continuation of the trachea. This anatomy predisposes the right lung to several problems:
- If food, liquids, or foreign bodies are aspirated, they often will lodge in the right mainstem bronchus. Aspiration pneumonia may result.
- If the endotracheal tube used for intubation is inserted too far, it usually lodges in the right mainstem bronchus. This allows ventilation of the right lung, but leaves the left lung useless.
Asthma
Asthma is hyperreactivity of the bronchi with an inflammatory component, often in response to allergens.
In asthma, the constriction of the bronchi can result in a difficulty in breathing giving shortness of breath; this can lead to a lack of oxygen reaching the body for cellular processes. In this case an asthma puffer can be used to rectify the problem. The puffer administers a bronchodilator, which serves to soothe the constricted bronchi and to re-expand the airways. This effect occurs quite quickly.
Additional images
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Transverse section of thorax, showing relations of pulmonary artery
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Illustration depicting respiratory system
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Mainstem bronchi seen branching off the trachea (labeled at top), with the left mainstem bronchi passing below the aortic arch before branching into smaller bronchi.
References
- ^ Maton, Anthea; Jean Hopkins; Charles William McLaughlin; Susan Johnson; Maryanna Quon Warner; David LaHart; Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. [page needed]
- ^ Brodsky, JB; Lemmens, JM (2003). "Left Double-Lumen Tubes: Clinical Experience With 1,170 Patients" (PDF). Journal of Cardiothoracic and Vascular Anesthesia 17 (3): 289–98. doi:10.1016/S1053-0770(03)00046-6. PMID 12827573.
- ^ a b Marieb, Elaine N.; Hoehn, Katja (2012). Human Anatomy & Physiology (9th ed.). Pearson. ISBN 0321852125.
- ^ Shih, Fu-Chieh; Wei-Jing Lee; Hung-Jung Lin (2009-03-31). "Tracheal bronchus". Canadian Medical Association Journal 180 (7): 783–783. doi:10.1503/cmaj.080280. ISSN 0820-3946.
- ^ Barat, Michael; Horst R. Konrad (1987-03-04). "Tracheal bronchus". American Journal of Otolaryngology 8 (2): 118–122. doi:10.1016/S0196-0709(87)80034-0. ISSN 0196-0709. Retrieved 2011-05-17.
Sources
- Sacristán Bou, L. and Peña Blas, F. Bronchial Atresia in Lung Diseases - Selected State of the Art Reviews (2012). ISBN 978-953-51-0180-2. Published under CC BY 3.0 license.
- Moore, Keith L. and Arthur F. Dalley. Clinically Oriented Anatomy, 4th ed. (1999). ISBN 0-7817-5936-6
External links
- American Lung Association
- Anatomy figure: 19:08-03 at Human Anatomy Online, SUNY Downstate Medical Center - "The divisions of the bronchus."
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General anatomy: systems and organs, regional anatomy, planes and lines, superficial axial anatomy, superficial anatomy of limbs
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Anatomy of the lower respiratory tract
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| Respiratory tree |
| Trachea |
- Tracheal rings
- Annular ligaments
- Carina
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| Bronchi |
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| Lungs |
| General |
- Landmarks
- Fissures
- Superior lobe
- Lingula of left lung
- Middle lobe of right lung
- Inferior lobe
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| BP segment |
- Bronchiole: Conducting zone (Terminal bronchiole)
- Respiratory zone (Respiratory bronchiole
- Alveolar duct
- Alveolus
- Blood-air barrier)
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| Cells |
- Alveolar cells
- Club cell
- Goblet cell
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Index of the respiratory system
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| Description |
- Anatomy
- Physiology
- Development
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| Disease |
- Congenital
- Neoplasms and cancer
- Chest trauma
- Infection
- common cold
- pneumonia
- tuberculosis
- Other
- Symptoms and signs
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| Treatment |
- Procedures
- Drugs
- nasal
- throat
- obstructive airway diseases
- cough and cold
- histaminergics
- pulmonary arterial hypertension
- other
- Surgery
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