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, page 221), 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 membrane 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.
Elastic fbers, dermis, monkey, Welgert’s ×160.
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
KEY BV, blood vessel C, collagen fibers D, duct of sweat gland E, elastic fibers PLATE 6 • E LASTIC FIBERS AND E LASTIC LAM E LLAE
Elastic fbers, mesentery, rat, Weigert’s ×160. beginnings or endings and with a somewhat irregular course. Again, the collagen fibers (C) are contrasted by their eosin staining and appear as long,
This is a whole mount specimen of mesentery prepared to straight profiles that are considerably thicker than the elastic fibers.
show the connective tissue elements and differentially stained to reveal elastic fibers. The elastic fibers (E) appear as thin, long, crisscrossing and branching threads without discernible
Elastic lamellae, elastic artery, monkey, Weigert’s ×80.
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.