Pseudostratified Columnar Epithelium

The cells of pseudostratified columnar epithelium appear stratified or layered, but they are not. A layered effect occurs because the nuclei are at two or more levels in the row of aligned cells. However, the cells, which vary in shape, all reach the basement membrane, even though some of them may not contact the free surface.

Figure 5.3

Simple columnar epithelium consists of a single layer of elongated cells (400x)

Mucus

Surface of tissue Goblet cell Nucleus Cytoplasm Basement membrane Connective tissue

Figure 5.3

Simple columnar epithelium consists of a single layer of elongated cells (400x)

Figure

A scanning electron micrograph of microvilli, which fringe the exposed surfaces of some columnar epithelial cells (33,000x).

Figure

A scanning electron micrograph of microvilli, which fringe the exposed surfaces of some columnar epithelial cells (33,000x).

The cells of pseudostratified columnar epithelium often are fringed with cilia. The cilia extend from the free surfaces of the cells. Goblet cells scattered throughout this tissue secrete mucus, which the cilia sweep away (fig. 5.5).

Pseudostratified columnar epithelium lines the passages of the respiratory system. In the respiratory passages, the mucus-covered linings are sticky and trap dust and microorganisms that enter with the air. The cilia move the mucus and its captured particles upward and out of the airways.

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