INTERRELATIONS 401 



Action of the Thyroid on the Thymus 



For the anatomical and embryological relationship between 

 thyroid and thymus see p. 277 et seq. The thyroid secretion 

 affects the growth of the thymus gland, which has been found 

 to undergo an increase in size in fcetal animals after thyroid 

 feeding of the pregnant mother (guinea-pigs). In exoph- 

 thalmic goitre the thymus is often hypertrophied and has been 

 supposed to take a part in producing the symptoms of the 

 disease. But not only in Graves's disease does thymus hyper- 

 trophy occur ; it may also be associated with simple congenital 

 goitre. It is not clear whether thyroidectomy causes thymus 

 atrophy. 



Action of the Thyroid on the Pancreas 



It is well known that the thyroid has some influence on 

 carbohydrate metabolism, and this is often explained as indi- 

 cating a relation between the thyroid and the pancreas. But 

 Krause and Cramer find that when small amounts of fresh 

 thyroid gland are administered for two or three days to rats 

 or cats fed on a carbohydrate-rich diet, the liver will be found 

 to contain only traces of glycogen. This effect is due to an 

 inhibition of the glycogenic function of the liver, not to an 

 increased utilization of carbohydrates. It is not accompanied 

 by glycosuria, and (in dogs) the tolerance for glucose is only 

 slightly diminished by thyroid feeding. 



If the parathyroids are removed also, the assimilation limit 

 for sugar is distinctly lowered and the injection of adrenin then 

 produces more pronounced glycosuria than in the normal 

 animal. This is usually quoted as one of the instances of an 

 antagonistic action between thyroids and parathyroids. The 

 experiments involving removal of thyroids without the para- 

 thyroids are notoriously difficult, and much further evidence 

 is required on the subject. 



Some observers have reported an increase in the islets of 

 Langerhans after thyroidectomy. 



Notwithstanding the meagre character of the evidence, the 

 majority of modern writers seem fully to accept the view that 

 the thyroid has a direct inhibitory influence upon the pancreas, 

 and affects carbohydrate metabolism through the internal 

 secretion of this organ. 



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