510 



THE CELL AND MAMMALIAN HISTOLOGY 



extent of the secretory surface various names are given to glands ; 

 some are shown in Fig. 397. Many of the endocrine glands, 



Fig. 396.— Diagram to illustrate the cycle of activity in a secretory cell. Efferent 

 nerve fibres, blood capillaries, and (on a deeper plane) a lymphatic plexus are 

 shown. * *, basement membrane. The cell on the extreme left shows the Golgi 

 apparatus '; secretory granules appear around this, some of them become 

 liquefied, and (on the right) thev are discharged from the cell. — From Le Gros 

 Clark, The Tissues of the Body, 3rd edition, 1952. Clarendon Press, Oxford. 



which produce hormones (pp. 470-472), begin as ordinary 



epithehal glands with ducts ; when they lose these the cells 



discharge their products either 



into small intercellular spaces 



or into relatively large 



vesicles, and from both of 



these the secretion passes to 



the blood stream. The islets of 



Langerhans consist of solid 



masses of cells which have 



lost much of their epithelial 



appearance while retaining its 



character, and the thyroid 



has vesicles surrounded by a 



single layer of cubical cells 



with conspicuous nuclei. 



Other endocrine glands, such 



as the posterior pituitary 



and adrenal medulla which 



are derived from nervous 



tissue, and the interstitial 



C D 



Fig. 397. — Diagrams of different kinds 

 of glands. — Partly after Lang. 



A, Columnar epithelium containing isolated gland 

 cells or unicellular glands. B, similar epithelium 

 with the gland cells collected into a group so 

 as to form a flat multicellular gland. C, a 

 hollow multicellular gland of the simple kind. 

 D, the compound or racemose glands. 



ah, Alveoh or acini of the racemose gland ; d., 

 ducts ; /., alveolus or fundus of simple gland ; 

 g.c, gland cells. 



