Elastic fibers are present in loose and dense connective tissue throughout the body, but in lesser amounts than collagenous fibers. Elastic fibers are not conspicuous in routine H&E sections but are visualized readily with special staining methods. (The following selectively color elastic material: Weigert's elastic tissue stain, purple-violet; Gomori's aldehyde fuchsin stain, blue-black; Verhoeff's hematoxylin elastic tissue stain, black; and modified Taenzer-Unna orcein stain, red-brown.) By using a combination of the special elastic stains and counterstains, such as H&E, not only the elastic fibers but also the other tissue components may be revealed, thus allowing study of the relationships between the elastic material and other connective tissue components.
Elastic material occurs in both fibrous and lamellar forms. In loose and dense connective tissue and in elastic cartilage (see Plate 9), the elastic material is in fibrous form. Similarly, the elastic ligaments that connect the cervical vertebrae and that are particularly prominent in grazing animals have a mixture of elastic and collagenous fibers in a tightly packed array. In the major, largest diameter arteries (e.g., aorta, pulmonary, common carotid, and other primary branches of the aorta), the tunica media consists of fenestrated layers of elastic tissue alternating with layers containing smooth muscle cells and collagenous tissue. This allows stretching and elastic rebound to assist in the propulsion of the blood. All arteries and most large arterioles have an internal elastic lamina that supports the delicate endothelium and its immediately subjacent connective tissue. It should be noted that both the collagen and elastic components of the tunica media are produced by the smooth muscle cells of this layer.
Figure 1, dermis, monkey, Weigert's x160.
This shows the connective tissue of the skin, referred to as the dermis, stained to show the nature and distribution of the elastic fibers (E), which appear purple. The collagen fibers (C) have been stained by eosin, and the two fiber types are easily differentiated. The connective tissue at the top of the figure, close to the epithelium (the papillary layer of the dermis), contains thin elastic fibers (see upper left of figure) as well as less coarse collagen fibers. The lower por-
Figure 2, mesentery, rat, Weigert's x160.
This is a whole mount specimen of mesentery, similar to Figure 2 in Plate l but prepared to show the connective tissue elements and differentially stained to reveal elastic fibers. The elastic fibers (E) appear as thin, long, criss-
Figure 3, artery, monkey, Weigert's x80.
Elastic material also occurs in sheets or lamellae rather than string-like fibers. This figure shows the wall of an elastic artery (pulmonary artery) that was stained to show the elastic material. Each of the wavy lines is a lamella of elastic material that is organized in the form of a fenestrated sheet or membrane. The plane of section is such that the elastic membranes are seen on edge. This specimen was not subsequently stained with H&E. The empty-appearing tion of the figure shows considerably heavier elastic and collagen fibers. Also note that many of the elastic fibers appear as short rectangular profiles. These profiles simply represent fibers traveling through the thickness of the section at an oblique angle to the path of the knife. Careful examination will also reveal a few fibers that appear as dot-like profiles. They represent cross-sectioned elastic fibers. Overall, the elastic fibers of the dermis have a three-dimensional interlacing configuration, thus the variety of forms.
crossing and branching threads without discernable beginnings or endings and with a somewhat irregular course. Again, the collagen fibers (C) are contrasted by their eosin staining and appear as long, straight profiles that are considerably thicker than the elastic fibers.
spaces between elastic layers contain collagen fibers and smooth muscle cells, but they remain essentially unstained. In the muscular layer of blood vessel, both elastin and collagen are secreted by the smooth muscle cells.
Tissues of the body containing large amounts of elastic material are limited in distribution to the walls of elastic arteries and some ligaments that are associated with the spinal column.
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