Collagen

A long, insoluble fibrous structural protein found in the extracellular matrix and in connective tissue, having different functions than those of globular proteins such as enzymes.  In fact, it is one of the most common proteins in mammals, making up some 25% of the total number of proteins in the body.  It consists of bundles of collagen referred to as ‘collagen fibers’, which, by means of a strict interactive arrangement form collagen rods.  This arrangement provides collagen with great tensile strength and resistance to stretching in cartilage, ligaments, tendons and bones.  However, it forms a necessary liaison with elastin in supporting the tissues of the body: while collagen ensures firmness and strength, elastin provides the same tissues with flexibility.  This partnership is not only crucial for the optimal functioning of cartilage and the likes, but also to those of the lungs and blood vessels.  In total, there are more than 20 different types of collagen, but more than 90% of the collagen in the body is of Type I (that found in bones, cartilage, tendons an skin).  In the past, it was believed that all collagens were formed by secretions from fibroblasts, but now it is clear that this is the function of various epithelial cells (closely packed cells that form the epithelium).  Collagen plays important roles in the growth of bones and tissue across the life span.  With ageing, it is progressively lost, resulting in osteoporosis or brittle bones.