SECTION VII 



INTERNAL SECRETIONS OR HOEMONES- 

 THEIR PRODUCTION AND ACTION 



THE products of the metabolism of the various organs are carried 

 away in the lymph and blood, and certain of these products 

 exercise an important influence upon other structures in the 

 body. Thus, the carbon dioxide produced in muscle acts 

 upon and stimulates the respiratory centre, and the secretion 

 formed in the lining membrane of the duodenum stimulates 

 the pancreas. These products have been termed Internal 

 Secretions, while more recently the name Hormones or " Activ- 

 ators " has been suggested for them. 



Among the structures which are known to yield such 

 hormones are : 



1. Suprarenal Bodies. These structures lie just above the 

 kidneys. Each consists of a tough cortex composed of epithelial- 

 like cells arranged in columns, and a soft medulla consisting of 

 cells derived from neuron cells which stain of a peculiar brown 

 colour with chromic acid. The medulla is developed from the 

 sympathetic chain of ganglia. The cortex is a perfectly in- 

 dependent structure derived from the surrounding mesoblast, 

 and in teleostean fishes it is quite apart from the representative 

 of the medullary part. A suprarenal body is thus two distinct 

 and independent organs combined with one another (fig. 163). 



Long ago Brown-Sequard found that removal of these bodies 

 causes great muscular weakness, loss of tone of the vascular 

 system, loss of appetite, and finally death in a short time. 

 Addison had already pointed out that a similar set of symptoms, 

 accompanied by pigmentation of the skin, is associated with 

 diseased conditions of these organs in mWi. The injection of 

 small quantities of the medullary portion of the bodies or of 

 extracts of it exercises a powerful effect on the endings of the 

 thoracico-abdominal visceral nerves. The most marked result 

 is to cause contraction of the arterioles and an enormous rise 



