What are the two types of fibres of connective tissues? Distinguish between the two.

Collagenous Fibers

Collagenous fibers consist of types I, II, or III collagen and are present in all types of connective tissue. Collagenous connective tissue is divided into two types, based upon the ratio of collagen fibers to ground substance:

• Loose (areolar connective tissue) is the most abundant form of collagenous connective tissue. It occurs in small, elongated bundles separated by regions that contain ground substance.
• Dense connective tissue is enriched in collagen fibers with little ground substance. If the closely packed bundles of fibers are located in one direction, it is called regular; if oriented in multiple directions, it is referred to as irregular. An example of regular dense connective tissue is that of tendons; an example of irregular dense connective tissue is that of the dermis.

Reticular Fibers

Reticular fibers are composed of type III collagen. Unlike the thick and coarse collagenous fibers, reticular fibers form a thin reticular network. Such networks are widespread among different tissues and form supporting frameworks in the liver, lymphoid organs, capillary endothelia, and muscle fibers.

Elastic Fibers

Elastic fibers contain the protein elastin, which co-polymerizes with the protein fibrillin. These fibers are often organized into lamellar sheets, as in the walls of arteries. Dense, regular, elastic tissue characterizes ligaments. Elastic fibers are stretchable because they are normally disorganized – stretching these fibers makes them take on an organized structure.