Page 87 - Atlas of Histology with Functional Correlations

Microvilli

In contrast to cilia, microvilli are nonmotile. Microvilli are highly developed
on the apical surfaces of epithelial cells of the small intestine and kidney.
Here, the main functions of the microvilli are to absorb nutrients from the

digestive tract of the small intestine or the glomerular filtrate in the kidney.

FIGURE 2.4 | Junctional Complex Between

Epithelial Cells

A high-magnification electron micrograph illustrates a junctional complex
between two adjacent epithelial cells. In the upper or apical region of the cells,

the opposing cell membranes fuse to form a tight junction or zonula occludens
(2a), which extends around the cell peripheries like a belt. Inferior to the zonula
occludens (2a) is another junction called the zonula adherens (2b). It is
characterized by a dense layer of proteins on the inside of the plasma membranes
of both cells, which attach to the cytoskeleton filaments of each cell. A small

intercellular space with transmembrane adhesion proteins separates the two
membranes. This type of junction also extends around the cells like a belt. Below
the zonula adherens is a desmosome (2c). Desmosomes (2c) do not encircle the

cells, but are spotlike structures that have random distribution in the cells. The
cytoplasmic side of each desmosome exhibits dense areas composed of
attachment proteins. Transmembrane glycoproteins extend into the intercellular
space between opposing cells membranes of the desmosome and attach the cells
to each other.

Note also in the micrograph the distinct cell membranes (3) of each cell, the
numerous mitochondria (1) in cross section, and a variety of vesicular
structures (6) in their cytoplasm. Visible on the cell apices are sections of cilia
(5) with a core of microtubules and a few microvilli (4).

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