This is sometimes referred to as fatty connective tissue . Common examples include bone, tendons, ligaments, and fibrous capsules encasing visceral organs. Collagen belongs to a family of insoluble fibrous proteins synthesized by a connective tissue cell called a fibroblast . Collagen is often organized into long, dense, closely packed bundles of interlinked fibers. Collagen is a major constituent of bone, cartilage, ligaments, tendons, dermis, visceral capsules, as well as scar tissue.
Reticular fibers are also abundant in the smooth muscle of arteries, bone marrow, spleen, and liver.
The other major fibrous protein in the extracellular matrix is elastin . Unlike collagen, which is organized into dense fibrous bundles, elastin is somewhat amorphous and arranged in relaxed cross-linked coils. When elastic tissue is stretched, the elastin molecule is elongated into a more linear conformation. When the stretching force is released, the elastin returns to the more stable random-coil structure. In this respect, elastin fibers function much like rubber bands.