Page 86 - Atlas of Histology with Functional Correlations

FIGURE 2.3 ■ Internal and external morphology of ciliated and nonciliated

epithelium. ×11,000.

FUNCTIONAL CORRELATIONS 2.4 ■ Cilia and

Microvilli

Cilia are highly motile surface modifications in cells that line the respiratory
organs, oviducts or uterine tubes, and efferent ducts in the testes. Cilia are

inserted into the basal bodies beneath the cell membrane. The main function
of cilia is to sweep or move fluids, cells, or particulate matter across cell
surfaces. In the lungs, the cilia rid the air passages of particulate matter or

mucus. In the oviduct, cilia move eggs and sperm along the passageway, and
in the testes, cilia move mature sperm into the epididymis.

The motility exhibited by cilia is caused by the sliding of adjacent
microtubule doublets in the core of the cilia. Each of the nine doublets in the
cilia consists of two subfibers called A and B. Extending from the A subfiber

are two armlike filaments containing the motor protein dynein, which
exhibits ATPase activity. This protein uses the energy of ATP hydrolysis to
move cilia. Dynein armlike extensions from one doublet temporarily attach
and detach from the subfiber B of the adjacent doublet, producing a sliding

force between the doublets. These rapid back-and-forth changes between
adjacent doublets produce cilia motility.

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