Slide 12 - stretched whole mount of Areolar Connective Tissue prepared with H&E and Verhoeff’s specific elastic stain.  Look with high power for the details of fiber content in this tissue.

Elastic fibers are dark purple and very thin and fine; they are sometimes branched, seen stretched and straight, and sometimes have snapped and become curled.  The collagenous fibers are pink, of varying thickness, and often wavy, showing individual parallel strands.  The fibers in areolar connective tissue run in all directions.  Cells are scattered randomly and are not well preserved here; most of the ones with pale, oval nuclei are fibroblasts.

Collagenous fibers are termed white fibers because this is their color when seen in bulk, as in tendons.  They contain collagen and are fibrillar in structure.  They stain pink in H&E; green or blue in special connective tissue stains, such as Mallory’s.  Read about the periodicity of collagen microfibrils as seen in electron microscopy.

Elastic fibers are termed yellow fibers because of their color in bulk.  They contain elastin, are refractile and are not fibrillar.  Although they stain like collagenous fibers in ordinary H&E, they can be best shown with specific elastic stains like orcein  (brown or purple depending in part on the counterstain).

Reticular fibers (Type III Collagen) are the most delicate strands of collagen fibrils.  They can be readily seen in areolar c.t. with EM but only when silvered with light microscopy.  Like all collagen and elastic fibrils, they are produced by fibroblasts.  In most of the body, reticular fibers form the finest, most delicate portion of areolar connective tissue, and are found directly underlying epithelium, wrapping immediately around capillaries, supporting individual fat cells, etc.  These fibrils are continuous with the thicker Type I collagen fibers of the rest of the areolar supporting tissue.

Reticular Tissue:  This delicately supportive tissue is found only in lymphoid and blood-forming areas of the adult (lymph node, spleen, bone marrow).  Since all of the very fine fibrils in this meshwork (or stroma) are collagenous (Type III) and must be silvered to be visible with light microscopy, they are called reticular fibers.  Also the fibroblast-like cells that produce them (in just these special instances) are called reticular cells. The cytoplasmic extensions of these stellate reticular cells form a second meshwork of their own, to further support the developing blood cells.  (The Latin word for meshwork or network is reticulum).