«tasdiqlayman» Tabiiy fanlar fakulteti dekani K. Asqarov

Microanatomy[edit]
Main article: Respiratory epithelium
The cartilage and mucous membrane of the main bronchus (primary bronchi) are similar to those in the trachea. They are lined with respiratory epithelium, which is classified as ciliated pseudostratified columnar epithelium.^[7] 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 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 cuboidal epithelium, to simple squamous epithelium in the alveolar ducts and alveoli.^[7][8]
Variation[edit]
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 hemoptysis.^[13][14] In about half of observed cases the cardiac bronchus presents as a short dead-ending bronchial stump, in the remainder the bronchus may exhibit branching and associated aerated lung parenchyma.
Function[edit]
See also: Respiratory tract § Lower respiratory tract
The bronchi function to carry air that is breathed in through to the functional tissues of the lungs, called alveoli. 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. The alveolar ducts and alveoli consist primarily of simple squamous epithelium, which permits rapid diffusion of oxygen and carbon dioxide.
Clinical significance
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]