Internal secretion and the ductless glands / by Swale Vincent ; with a preface by E.A. Schäfer.

  • Vincent, Swale, 1868-1934.
Date:
1922
Catalogue details

Licence: In copyright

Credit: Internal secretion and the ductless glands / by Swale Vincent ; with a preface by E.A. Schäfer. Source: Wellcome Collection.

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    beneath the membrane are found blood capillaries and lymph spaces. When such a layer of epithelial cells becomes invaginated, we have a tubule or saccule possessing a lumen, and forming a simple tubular or saccular gland. Such glands may be coiled, as in the case of the sweat glands, or the secretory portions of the glands may divide, forming branched tubular glands. This branching may occur again and again, until a complicated structure is produced (compound tubular and compound saccular [or racemose] glands). In these glands the terminal portion of the tubes or “ alveoli ” are the secre¬ tory portions, while the tubes leading to the exterior are the “ ducts.” The gland cell varies in its microscopic appearance, according to its functional condition. In the submaxillary gland and in the pancreas the variations are well known and easily observed—the discharge of the zymogen granules and the resulting changes in the appearance of the secreting cells. Similar functional changes may be observed in the epithelium of the intestine. But it was discovered that some of these glands possessed no duct, and they were therefore called “ ductless glands,” or in German more usually “ Blutgefassdrusen,” or “ Blutdriisen.” The latter names are, however, rapidly falling into disuse, and the terms, “ductless glands,” or “glands with an internal secretion,” are replacing them. The assumption was at once made that, since these structures had the characters of glands, they must “ secrete.” But since there was no communication with a free surface, the hypothesis soon arose that in these cases the specific secretion is passed into the blood-stream, and both the process and the product were termed “ internal secretion.” Thus a new conception in regard to the physiological nature of secretion sprang into existence, and the definition of a gland was extended so as to apply to any structure made up of one or more cells of a special epithelial character which form a product—the secretion—which is discharged upon a free epithelial surface, such as the skin or mucous membrane, or upon the closed epithelial surface of the blood cavities. In some cases the material secreted by the ductless glands has been supposed to be passed away not directly into the blood-stream, but indirectly by means of the lymphatics. This was formerly believed to apply to the specific secretion of the thyroid gland (see, however, p. 307).