Bone Growth and Maturation

Abstract

Growth is commonly defined as an increase in size, but more specificity is needed. An increase in size of the whole body or of an organ such as a bone may be caused by one or a combination of three processes: (1) Hyperplasia, or an increase in cell number, which involves duplication of DNA and cellular division; (2) Hypertrophy, or an increase in cell size, with true hypertrophy implying an increase in the size of the active functional elements of a cell, such as occurs in skeletal muscle with exercise; and (3) Storage of organic or nonorganic materials within or among cells. Each of these three processes occurs during bone growth, but the extent to which any one of them dominates depends on age or maturity and the part of the bone considered. Furthermore, these processes are often reversed in localized areas. While the overall change is an increase in size, some parts of a bone may become smaller or may be removed completely. In such areas, there is a reduction in cell number or cell size or in the amounts of organic or nonorganic material that are stored. Commonly, all these processes are combined.