Page 268 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

250 Veterinary Histology of Domestic Mammals and Birds

contraction of the bronchial muscles (Figures 11.17 and Bronchioles (bronchioli veri, bronchioli
VetBooks.ir 11.18). terminales)
Incomplete rings of hyaline cartilage form the struc-
In the bronchioles, the lumen of the conducting airways is
tural core of the bronchi. Near the trachea, they are almost reduced to a diameter of less than 1 mm. The wall of the
complete. With increased branching of the bronchial tree, small bronchioles (bronchioli veri) and terminal bronchi-
the rings become smaller and less substantial (cartilage oles (bronchioli terminales) comprises:
‘plates’), eventually becoming fragmented. The cartilage
fragments are connected by predominantly elastic fibres · ciliated epithelium with Clara cells,
that project into the perichondrium, contributing to the · lamina propria with elastic fibres and smooth muscle
flexibility of the bronchi. The smallest, most peripheral cells surrounded by loose connective tissue and
cartilage fragments are composed of elastic cartilage. The · no glands or cartilaginous elements.
tunica adventitia contains connective tissue, vessels and
nerves (Figures 11.16 to 11.19).

11.17 Lung (ox). Bronchi are characterised by the presence of mixed glands and hyaline cartilage rings or frag-
ments. Haematoxylin and eosin stain (x30).

11.18 Lung (calf). The staining technique used in this section highlights the elastic fibres, which are particularly
prominent in the larger bronchial branches. Resorcin–fuchsin–nuclear-fast red (Weigert’s elastic) stain (x30).

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