Respiratory epithelium, trachea.
that lines the inner surface of the respi-
ratory tract. It is composed of several types of cells:
Ciliated columnar cells
are tall and have long,
actively motile cilia, which help to move mucus and trapped
dust toward the mouth.
are goblet-shaped cells
without cilia; they secrete mucus onto the surface of the epi-
thelium. The mucus captures dust particles when air passes
through the trachea.
are short cells capable of
differentiating into other cell types in the epithelium.
have a round, dark nucleus with clear cytoplasm and
contain granules at the basal region of the cytoplasm fac-
ing the basement membrane. These cells secrete serotonin
and peptide hormones that act as local mediators. This may
affect nerve endings as well as regulate mucous secretion
and ciliary beating of nearby cells.
The epithelium that lines the nasal cavities, trachea, bronchi, and larger bronchioles has a characteristic composition of cell types
pseudostratif ed columnar epithelium
are the most prominent cell types, and they function
together to generate a mechanism called the
, which functions to entrap airborne debris in mucus and transport
it along the surface toward the oral cavity. The numerous cilia projecting from the apical surface of the ciliated cells (most abundant
cell type) beat in a coordinated fashion to move material toward the oropharynx. Parts of
are visible at the bottom of the
F eld; these serve as stem cells for replacement of the other cell types. Not visible here are two other cell types that occur in lower
numbers in respiratory epithelium.
are columnar cells with microvilli at the apical surface. These cells are contacted by
nerve endings, indicating a sensory function.
are the F
fth cell type; they are short basal cells with small cytoplasmic granules
that contain signaling molecules. (±or microstructure of cilia, see ±ig. 3-12A.)