Page 11 - Module 1-Anatomy and Physiology of Growth Hormone Function Final (Interactive)

Module 1: Anatomy and Physiology of Growth Hormone

Anatomy of the Growth Plate

The growth plate is the final target organ for longitudinal growth and which results
from chondrocyte proliferation and differentiation. During the first year of life,
longitudinal growth rates are high, followed by a decade of modest longitudinal
growth. The age at onset of puberty and the growth rate during the pubertal growth
spurt (which occurs under the influence of estrogens and GH) contribute to sex
differences in final height between boys and girls. At the end of puberty, growth
plates fuse, thereby ceasing longitudinal growth. It has been recognized that
receptors for many hormones such as estrogen, GH, and glucocorticoids are present
in or on growth plate chondrocytes, suggesting that these hormones may influence
processes in the growth plate directly (Figure 5).

Figure 5. Pituitary hormones and target organs

As illustrated in Figure 5, the growth plate is a highly organized cartilaginous
structure located between the epiphyseal and metaphyseal bone at the distal ends of
the long bones. Longitudinal growth takes place by a process called endochondral
ossification, in which a cartilaginous scaffold is replaced by bone in a coordinated
fashion. The growth plate can be divided into horizontal zones of chondrocytes at
different stages of differentiation.

GH acts on its target tissue either directly or indirectly through IGF-1. GH acts on
resting zone chondrocytes and is responsible for local IGF-1 production. IGF-1 is
also responsible for stimulating chondrocyte hypertrophy.

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