CHAPTER XV. 

 THE DUCTLESS GLANDS. 



THE ductless glands include a group of organs of very varied functions, 

 the only feature which they have in common being the absence of any 

 secretion passing either to the surface of the body or into the digestive 

 tract. Many of them, however, such as the thyroid, suprarenal, and 

 pituitary glands, do form substances which pass either directly into the 

 blood stream or into the lymph channels and are described as internal 

 secretions. 



The internal secretions belong to the class of bodies known as 

 hormones, whose general characters have already been dealt with 

 (p. 306), and which are also formed by organs, e.g. the pancreas, which 

 possess an external secretion. The presence of these hormones in the 

 body is in many cases essential to health and even to life ; and the 

 activity of the internally secreting glands is correlated with and 

 regulates the functions of distant organs, the only link being the blood 

 by which the hormone is carried from its place of origin to its place of 

 action. 



Much of our knowledge of the functions of the ductless glands is 

 derived from the study of the symptoms observed in human beings, in 

 whom one or other of them is diseased. Hence it is usual in studying 

 their functions to consider (1) the effects of disease in these glands in 

 man, (2) the effect of their extirpation in animals, and (3) the effects of 

 extracts of the glands, either upon normal animals or as therapeutic 

 agents in man. 



THE SUPRARENAL GLANDS. 



One suprarenal gland lies at the upper end of each kidney. Each 

 consists of an outer yellowish cortex partially or completely enclosing 

 a darker central portion, the medulla. 



The cortex is composed of cells arranged in radial columns and 



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