Page 21 - Module 1-Anatomy and Physiology of Growth Hormone Function Final (Interactive)
P. 21

Module 1: Anatomy and Physiology of Growth Hormone



               Factors that Affect GH Action


               Factors such as age, gender, and body composition may have an effect on GH
               activity as well.

               Age

               GH has an influence on the body from birth through puberty until adulthood. In
               normal adults, the decline in GH levels with age is accompanied by a decline in
               serum IGF-1 levels.

               •  Longitudinal bone growth is stimulated by GH directly on the growth plate, IGF-1
                   produced locally in the growth plate in response to GH and by circulating IGF-1.
                   During puberty, there can be a 1.5- to 3-fold increase in the pulsatile secretion of
                   GH and a more than 3-fold increase in the concentration of serum IGF-1.
               It has also been shown that the breakdown in fat in response to GH administration
               appears to be higher in younger as compared to older subjects, in part because of
               differences in the amount of abdominal fat.
               Gender

               Both boys and girls increase their GH and IGF-1 output during puberty, but there are
               changes in body composition that are gender-specific:
               •  The larger skeletal muscle mass in males is the result of androgenic hormones
                   and a greater sensitivity to GH and IGF-1 produced as compared with females.
               •  Gender differences are also influenced by the earlier timing and completion of
                   puberty in the female.
               Females actually produce more GH than males and this difference is apparent even
               in puberty. However, despite the higher output of GH output in normal females, adult
               females receiving GH may be less sensitive to the metabolic effects of GH than
               males. Reference ranges for IGF-1 are shown in Tables 1 and 2.


               Table 1. Normal reference values for IGF-1 in pediatrics (Quest Diagnostics)


                     Pediatric         Male (ng/mL)        Female (ng/mL)
                     <1 Years             16-142                 17-185

                    1-1.9 Years           16-134                 16-175
                    2-2.9 Years           16-135                 16-178

                    3-3.9 Years           30-155                 38-214

                    4-4.9 Years           28-181                 34-238
                    5-5.9 Years           31-214                 37-272

                    6-6.9 Years           38-253                 45-316
                    7-7.9 Years           48-298                 58-367

                    8-8.9 Years           62-347                 76-424





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