§1.51 KINETIC HORMONES 9 



1.51 KINETIC HORMONES 



The kinetic hormones act upon effector cells or organs, to 

 produce repeatable reactions mainly concerned with feeding, 

 digestion and protective colour change, and so are often related 

 to the short-term interaction of the individual with its environ- 

 ment. The results that they produce are relatively rapid compared 

 with other types of hormone action, but considerably slower and 

 more long-lasting than the nerve action which often controls 

 similar effectors. Their action is also more widespread than that 

 of nerves, since they are distributed by the circulation throughout 

 the body, and cannot, as a rule, be used to cause the contraction 

 of one muscle and not another, or to produce a pattern by con- 

 centrating some chromatophores and dispersing others, unless the 

 effectors themselves are differentiated. 



Many, but by no means all, of the hormones in this group are 

 neurosecretory substances (2b. ii, p. 4). Most of the others 

 come from ectodermal glands (2b. iii), except the notable group 

 produced from the isolated cells (2b. i) in the mammalian gut. The 

 last-named are stimulated directly (§ 4.11); but the rest are all 

 controlled by the nervous system, apart from a few anomalous 

 hormones which appear to have kinetic actions but to be derived 

 from mesodermal glands (§ 4.324). 



There is one group of hormones within the kinetic type which 

 calls for special mention at this stage, and for an elucidation of the 

 rather confused nomenclature associated with it. These are the 

 hormones for which the name endocrinokinetic is adopted here. 

 They all stimulate the secretion of other hormones from endocrine 

 glands (2b. iii), and it seems logical to class this action, with that of 

 stimulating exocrine glands, as kinetic. But the situation in which 

 a series of two hormones is involved is more complex than those 

 with but one hormone, and it seems to warrant somewhat different 

 treatment. These endocrinokinetic hormones are frequently desig- 

 nated by the suffix ''trophic" or "tropic", as in thyrotrophic or 

 gonadotropic ; but the suffix is not confined to this type of hormone, 

 since it also occurs in chromatophorotrophic, where the effector 

 is a chromatophore, and not an endocrine gland at all. Even the 

 international decision taken in 1939 that the form trophic should 

 be used in all cases has led to no uniformity of spelling! 



