Biomedical Engineering Reference
In-Depth Information
II. STRUCTURE OF THE AIRWAY EPITHELIUM
A. Cell Types
The proximal airway epithelium is a pseudostratified epithelium composed
of basal cells, nonciliated columnar (secretory) cells, and ciliated columnar
cells (Fig. 1) (1). However, as many as eight different epithelial cells have
been described and the cellular composition of the epithelium varies with
location in the airway. The cellular composition of airway epithelium was
extensively reviewed by Harkema et al. (2).
Ciliated cells are thought to be nondividing, differentiated cells of the
epithelium (3). They have a columnar shape and attach to the basement
membrane. Ciliated cells have motile cilia on the apical surface, which
contains dynein, the motor molecule (4). Ciliated cells are damaged in
chronic bronchitis and COPD. The cilia themselves are shortened (5) and
there are fewer ciliated cells (6).
Mucous secreting goblet cells have secretory granules that produce
mucins, which are highly modified proteins resulting from the enzymatic
modification of several core peptides (7). Mucous secreting goblet cells are
columnar in shape and are present in large airways but less so in the term-
inal bronchioles where the predominant secretory cells are the Clara cells.
Figure 1
Normal human pseudostratified bronchial epithelium. Schematic drawing
of human airway epithelium. Typical epithelium contains a majority of ciliated
columnar cells and basal cells (which are thought to enhance the mechanical integrity
of the epithelium). There are varying amounts of mucous-secreting goblet cells
(see text.) Underlying mesenchymal cells include fibroblasts and smooth muscle cells.
