Bronchus

Source: Wikipedia, the free encyclopedia.
(Redirected from
Lobar bronchus
)
Bronchus
Bronchial vein
NervePulmonary branches of vagus nerve
Identifiers
Latinbronchus
MeSHD001980
TA98A06.4.01.001
A06.3.01.008
TA23226
FMA7409
Anatomical terminology]

A bronchus (

lower respiratory tract that conducts air into the lungs. The first or primary bronchi to branch from the trachea at the carina are the right main bronchus and the left main bronchus. These are the widest bronchi, and enter the right lung, and the left lung at each hilum. The main bronchi branch into narrower secondary bronchi or lobar bronchi, and these branch into narrower tertiary bronchi or segmental bronchi. Further divisions of the segmental bronchi are known as 4th order, 5th order, and 6th order segmental bronchi, or grouped together as subsegmental bronchi.[1][2]
The bronchi, when too narrow to be supported by cartilage, are known as bronchioles. No gas exchange takes place in the bronchi.

Structure

The

thoracic vertebra
(at rest).

The right main bronchus is wider, shorter, and more vertical than the left main bronchus,

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

right lung
. The left main bronchus divides into two secondary bronchi 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

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

seromucous glands, which secrete mucus, in its wall. Hyaline cartilage is present in the bronchi, surrounding the smooth muscle layer. In the main bronchi, the cartilage forms C-shaped rings like those in the trachea, while in the smaller bronchi, hyaline cartilage is present in irregularly arranged crescent-shaped plates and islands. These plates give structural support to the bronchi and keep the airway open.[5]

The bronchial wall normally has a thickness of 10% to 20% of the total bronchial diameter.[6]

Microanatomy

Main article: Respiratory epithelium
Cilia and much smaller microvilli on non-ciliated bronchiolar epithelium

The

mucins, the main component of mucus. Mucus plays an important role in keeping the airways clear in the mucociliary clearance
process.

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 ciliated cuboidal epithelium, to simple

squamous epithelium in the alveolar ducts and alveoli[7][8]

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.[9] 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.[10] [11]

The cardiac bronchus has a prevalence of ≈0.3% and presents as an accessory bronchus arising from the bronchus intermedius between the upper lobar bronchus and the origin of the middle and lower lobar bronchi of the right main bronchus.[12]

An accessory cardiac bronchus is usually an asymptomatic condition but may be associated with persistent infection or

lung parenchyma
.

Function

See also: Respiratory tract § Lower respiratory tract

The bronchi function to carry

squamous epithelium, which permits rapid diffusion of oxygen and carbon dioxide
.

Clinical significance

Bronchial wall thickness (T) and bronchial diameter (D).

Bronchial wall thickening, as can be seen on CT scan, generally (but not always) implies inflammation of the bronchi (bronchitis).[15] Normally, the ratio of the bronchial wall thickness and the bronchial diameter is between 0.17 and 0.23.[16]

Bronchitis

Main article: Bronchitis

Bronchitis is defined as inflammation of the bronchi, which can either be

chronic bronchitis also suffer from chronic obstructive pulmonary disease (COPD), and this is usually associated with smoking or long-term exposure to irritants
.

Aspiration

The left main bronchus departs from the trachea at a greater angle than that of the right main bronchus. The right bronchus is also wider than the left and these differences predispose the right lung to aspirational problems. If food, liquids, or foreign bodies are aspirated, they will tend to lodge in the right main bronchus. Bacterial pneumonia and aspiration pneumonia may result.

If a tracheal tube used for intubation is inserted too far, it will usually lodge in the right bronchus, allowing ventilation only of the right lung.

Asthma

Asthma is marked by hyperresponsiveness of the bronchi with an inflammatory component, often in response to allergens.

In asthma, the constriction of the bronchi can result in difficulty in breathing giving

lack of oxygen reaching the body for cellular processes. In this case, an inhaler can be used to rectify the problem. The inhaler administers a bronchodilator
, which serves to soothe the constricted bronchi and to re-expand the airways. This effect occurs quite quickly.

Bronchial atresia

Bronchial atresia is a rare congenital disorder that can have a varied appearance. A bronchial atresia is a defect in the development of the bronchi, affecting one or more bronchi – usually segmental bronchi and sometimes lobar. The defect takes the form of a blind-ended bronchus. The surrounding

tissue secretes mucus normally but builds up and becomes distended.[17] This can lead to regional emphysema.[18]

The collected mucus may form a mucoid impaction or a bronchocele, or both. A pectus excavatum may accompany a bronchial atresia.[17]

Additional images

  • Cross-section of secondary bronchus
    Cross-section of secondary bronchus
  • The left and right main bronchi sit behind the heart, shown here.
    The left and right main bronchi sit behind the heart, shown here.

Citations

  1. ISBN 978-1-4557-0418-7
    .
  2. ISBN 0-13-981176-1.[page needed
    ]
  3. PMID 12827573. Archived from the original (PDF) on 2017-03-12. Alt URL
  4. PMID 2642720
    .
  5. ISBN 9780073378251
    .
  6. ISBN 9781469824796
    .
  7. ^ a b Marieb, Elaine N.; Hoehn, Katja (2012). Human Anatomy & Physiology (9th ed.). Pearson.
    ISBN 978-0321852120
    .
  8. ^ "Bronchi, Bronchial Tree & Lungs". nih.gov. Retrieved 18 September 2019.
  9. ^ Weerakkody, Yuranga. "Tracheal bronchus | Radiology Reference Article | Radiopaedia.org". Radiopaedia. Retrieved 21 November 2021.
  10. PMID 19332762
    .
  11. ^ Barat, Michael; Horst R. Konrad (1987-03-04). "Tracheal bronchus". American Journal of Otolaryngology. 8 (2): 118–122.
    PMID 3592078
    .
  12. ^ "Cardiac bronchus". Radiopedia. Archived from the original on 2015-11-15.
  13. ISBN 3131390212
  14. PMID 8210391
    .
  15. ^ Weerakkody, Yuranga (2021-01-13). "Bronchial wall thickening". Radiopaedia. Retrieved 2018-01-05.
  16. ISBN 9780781757683
    .
  17. ^
    PMID 29302450
    .
  18. PMID 1494776
    .

Sources

External links

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