Page 172 - Atlas of Histology with Functional Correlations

Elastic Fibers

Elastic fibers are thin, small, branching fibers that are capable of stretching and
returning to their original length. They have less tensile strength than collagen
fibers and are composed of microfibrils and the protein elastin. When stretched,
elastic fibers return to their original size (recoil) without deformation. Elastic

fibers are found in abundance in the lungs, bladder wall, and skin. In the walls of
the aorta and pulmonary trunk, the presence of elastic fibers allows for stretching
and recoiling of these vessels during powerful blood ejections from the heart
ventricles. In the walls of the large vessels, the smooth muscle cells synthesize

the elastic fibers; in other organs, fibroblasts synthesize elastic fibers.

Supplemental micrographic images are available at
www.thePoint.com/Eroschenko13e under Connective Tissue.

FIGURE 5.2 | Loose Connective Tissue (Spread)

This composite image of mesentery was stained to show different fibers and
cells. Mesentery is a thin sheet of loose connective tissue that supports the
intestines of the digestive tract.

The pink collagen fibers (3) are the thickest, largest, and most numerous

fibers, and, in this preparation, the collagen fibers (3) course in all directions.

The elastic fibers (5, 10) are thin, fine, single fibers that are usually straight;
however, after tissue preparation, the fibers may become wavy as a result of the
release of tension. Elastic fibers (5, 10) form branching and anastomosing

networks. Fine reticular fibers are also present in loose connective tissue, but
these are not included in this illustration.

The permanent cells of connective tissues are the fibroblasts (2) that appear
flattened with an oval nucleus, sparse chromatin, and one or two nucleoli. Fixed
macrophages, or histiocytes (12), are always present in the connective tissue.

When inactive, they appear similar to fibroblasts, although their processes may
be more irregular and their nuclei smaller. Phagocytic inclusions, however, alter
the cytoplasm of the macrophages. In this illustration, the cytoplasm of different

macrophages (12) is filled with ingested, dense-staining particles.

Mast cells (1, 9) are also present in the loose connective tissue and are seen
as single or grouped cells along small blood vessels (capillary, 7). The mast

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