Page 45 - Headlines Histology2024_Neat

• With EM, elastic fibers have two main components: Elastin that appears as
an amorphous protein of low electron density. Microfibrils that are
embedded in the periphery of the fibers and occurring in small fascicles in
its interior.

• They are synthesized by fibroblasts and smooth muscle cells as tropoelastin.
The microfibrils are secreted prior elastin and provide scaffolding on which
elastin forms fibers and sheets.

3) Reticular fibers

• The reticular fiber form delicate network rather than coarse bundles around
capillaries, muscle cells, nerve, adipose cells and liver cells. They also
constitute the fibrous supporting tissue of endocrine, lymphoid and blood
forming organs.

• With LM, reticular fibers are not visible in H&E sections, but can be
selectively stains black by silver impregnation (hence the term argyrophilic
or argentaffin fibers) or with the periodic acid-schiff (PAS) reagent.

• The argyrophilia of reticular fibers as well as their PAS reactivity reside
mainly in the glycoprotein coat. When individual fibers are grouped to form
collagen fibers, the coating is removed and argyrophilia disappear.

• With EM, they are actually individual collagen fibrils (type III collagen)
coated by glycoproteins. They have the same 64-periodicity typical of
collagen fibrils.

III) Ground substance

• The ground substance is an amorphous gel-like material composed of
polysaccharide chains (glycosaminoglycans) bound to protein.

• With LM, in H&E sections, they are not visible when present in low
concentration. However, at higher concentration (as in hyaline cartilage),
they stain basophilic. When stained with toluidine blue or crystal violet,

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