5 - Endocrinology of Growth

Abstract

This chapter outlines the major factors that are involved in regulating fetal growth with particular emphasis on the insulin-like growth factor (IGF) axis. This allows comparing and contrasting the role of the IGF axis in the regulation of fetal and postnatal growth. The human growth process can be divided into three distinct phases of growthsuch as infancy, childhood, and puberty. These three phases are regulated by different aspects of the endocrine system. The growth in uterus and probably in the first 6 months of life is largely GH independent. The nutritional status of the individual is an important determinant, but the precise factors that translate nutrient input into growth remain to be defined. Transgenic technology coupled with knockout studies strongly suggest that the IGF axis plays an important role in this process. During the first year of life, there is a gradual switch from this nutritionally dependent growth process to GH dependency. Full dependence on GH for the growth process appears to be attained toward the second year of life, and thereafter the majority of childhood growth can be explained in terms of the amount of GH secreted by the individual. GH appears to be the final common pathway for integrating the effects of a number of growth signals. The pubertal growth spurt is made up by a contribution of sex steroids coupled with GH. The most important component appears to be estrogen in females and the aromatization of testosterone to estrogen in males.