BRONCHI

Anantomic features

Trachea divides into right and left primary (extrapulmonary) bronchi.
On entering the lungs the bronchi become the intrapulmonary bronchi.
The left bronchus divides into two lobar bronchial branches, the right - into three lobar bronchial branches.

The lobar bronchi of the left lung give rise to eight segmental bronchi, in right lung - to ten segmental bronchi.

MUCOSA

The height of the epithelial cells, and the thickness of basal lamina and lamina propria decrease as bronchi become reduced in diameter.

Composition:

Ciliated pseudostratified columnar epithelium with thick basement membrane

Cells:

Ciliated cells - the most numerous of the cell types, extend through the full thickness of the epithelium

Function: provide a coordinated sweeping motion of the mucus coat -"ciliary escalator" - that serves as an important protective mechanism for removing small inhaled particles

Mucus (goblet) cells - are interspersed among the ciliated cells and also extend through the full thickness of the epithelium

Function: unicellular mucin-secreting glands

Brush cells -columnar cells that bear microvilli. The basal surface is in synaptic contact with the afferent nerve endings

Function: receptor cells of general sensation

Small granule cells - their cytoplasm processes is sometimes observed extending to the lumen and cytoplasm contains numerous, membrane-bonded, dense-core granules

Function: release polypeptide hormones and/or catecholamines that are thought to function in reflexes regulating the airway or vascular caliber

Basal cells

Function: serve as a reserve population by maintaining individual cell replacement in the epithelium

Lamina propria

Function: conditioning (warming, moistening and removal of particulate materials) of the air, prevention the epithelium from dehydration by moving air

Composition: loose connective tissue containing numerous lymphocytes, lymphatic tissue in diffuse and nodular forms

MUSCULARIS

Function: maintenance of the appropriate diameter of the airway

Composition: continuous layer of smooth muscle in the larger bronchi. It is more attenuated in the smaller bronchi

SUBMUCOSA

Composition: loose connective tissue . Mucus-secreting glands and adipose tissue are present in the larger bronchi

CARTILAGINOUS LAYER

Composition: discontinuous hyaline cartilages plates that become reduced in size as the bronchial diameter diminishes

ADVENTITIA

Function: binds the bronchi to adjacent structures such as pulmonary artery and lung parenchyma

Composition: moderately dense connective tissue