Growth in childhood, one of the most fascinating, complex and dynamic biological processes, is tightly controlled and regulated. Growth evaluation, height and weight determinations, remains one of the most useful of all indices of public health and economic well being, specifically in developing countries and countries in transition.

This chapter does not intend to reduce to a brief summary the complex interactions involved in the processes of human growth and great scientific advances of the last decades. Rather, it aims to highlight two key themes. Firstly, the regulation and interaction of the main hormonal axis involved in human growth, the growth hormone (GH)-insulin-like growth factor axis (IGF-I) including the biochemical characteristics of the key members, the ontogeny and main modulators. An updated revision of the "somatomedin" hypothesis is presented. Secondly, current studies revisiting the organisation of normal growth from infancy into puberty are briefly discussed.

GH is important in promoting somatic growth and in regulating body composition, intermediary muscle and bone metabolism. Some of these GH effects are direct actions whereas others are mediated via IGF-I. IGF-I is the main effector of GH action in linear growth in man; in addition IGF-I and IGF-II are important growth factors involved in diverse cellular actions such as proliferation, differentiation and apoptosis.

This chapter should be read in conjunction with chapter 5c dealing with GH in the adult (link)