The basic components of extracellular space are mucopolysaccharides and fibrous proteins, particularly collagen and elastin. These proteins are synthesised in connective tissue and secreted out of the tissue. Collagen is predictable to form up to 40% of the body protein and fills the extracellular spaces. It has been recommended as the primary site of age related changes. Remember that collagen molecules are polymers of tropocollagen monomers. Newly polymerised molecules of collagen comprise non-covalent bonds and with age covalent cross-linking takes place between the monomers. Like the age of the organism increases cross-linking becomes much more hard to dissociate and by the time of maturity in mammals collagen becomes insoluble. From maturity to old age; cross-linking is strengthened and its effect can be computed. The age related changes in collagen are indisputable. Age related changes in the structure of collagen influence the functioning and structure of bones, tendon, blood vessels, joints, ligament etc. The inflexibility of collagen fibrils may be a contributory factor for the onset of atherosclerosis and hypertension.