The Biology of Senescence 



a minimum output of thyroid hormone is required to maintain 

 growth and development. At puberty, in response to the 

 pituitary gonadotropins, the gonads produce steroid hormones 

 which directly stimulate the growth of bone and of soft tissues. 



Fig. 42. — The postnatal growth in weight of male children (kg/years) 

 (from the data of Quetelet) . 



300 ~ 



2 3 t 5 6 ? 6 9 10 11 12 f3 14 15 IS 17 18 13 20 21 22 



Age in Years from Birth 



Fig. 43. — Annual growth increment in boys, from the data of Quetelet 

 k r k 4 = growth constants at each period (from Schmalhausen, 1928). 



The process of bone growth in man is, however, self-limited, 

 since the same hormones produce skeletal maturation and 

 fusion of the epiphyses. There is reason to suspect that they 

 also inhibit the production of pituitary growth hormone— 



184 



