Generally, tissues heal faster and leave less obvious scars in the young than in the aged. In fact, surgery performed on the fetuses leaves no scars. The younger body is generally in a better nutritional state, its tissue have a better blood supply and its cells have a higher metabolic rate compared with the old. Thus cells can synthesize needed materials and divide more quickly. The extracellular components of tissue also changes with age. Glucose, the most abundant sugar in the body, plays a role in the aging process. As the body ages, glucose is haphazardly added to proteins inside and outside the cells, forming irreversible cross-links between adjacent proteins molecules. With advancing age, more cross-links form, which contribute to the stiffening and loss of elasticity that occurs in aging tissues. Collagen fibers, responsible for strength of tendons, increase in number and change in quality with aging. These changes in the collagen of arterial wall effect the flexibility of arteries as much as the fatty deposits associated with atherosclerosis. Elastin, another extracellular component, is responsible for the elasticity of blood vessels and skin. It thickens, fragments and acquires a greater affinity for calcium with age-changes that may also be associated with atherosclerosis.