The influence of certain endocrine glands upon growth and development

Abstract

BEFORE considering the specific structure and functions of the endocrine glands, with particular reference to growth and development, it might be well to consider just what is meant by an endocrine or ductless gland. It has long been known, in fact it was demonstrated as early as 1849 by Berthold in his transplantation experiments of the cock's testis, that this gland had an influence by virtue of its growth in the new individual. Although at that time the exact nature was not understood, we now speak of the secretion from such glands as an internal secretion meaning thereby that the specific substance elaborated by the gland is absorbed directly into the blood and lymph and thus gains access to all parts of the body, the final clinical effect being produced by changes in various parts of the body. This idea of an internal secretion was given a further impulse by Bernard's classical investigations on hepatic function showing an internal secretion which is called glycogen in addition to the well-known external secretion, the bile, which is passed through the bile ducts into the intestine. Certain of the glands in the body have only an internal secretion such as the pituitary gland, the thyroid, possihly the thymus and the adrenal glands. Some have both an external and an internal secretion such as the pancreas, which elaborates the digestive enzymes which are carried in the pancreatic juice to the intestine and an internal secretion elaborated by the well-known structures, called the islets of Langerhans, which structures have no connection with the excretory ducts of the pancreas, but pass their secretion of hormone which has an important carbohydrate regulatory function, directlv into the blood stream. It is probable that the ovary and testis should be placed in this same group since we may regard the ovum and spermatozoon as representing the external secretion, whereas, we all know the importance of the internal secretion of both these glands in producing the important changes seen in both males and females, particularly at the time of puberty. On the other hand there are certain glands, which as far as we know, have only an external secretion. However there are those who feel that even these glands have important internal secretory function. '1'0 this gronp belong the lacrimal and the salivary glands. An endocrine gland then, as the derivation of the name implies, is one which elaborates a secretion which is usua llv of a complex chemical nature, which is poured directly into the blood stream and which produces its effect by chemical changes within the blood and tissues of the body.