52 SOURCES OF KINETIC AND METABOLIC HORMONES 



in Amia, but most teleosts have only one pair. Histologically their 

 cells look like cortical tissue ; but they do not seem to respond to 

 ACTH, and their function is uncertain. Their homology with true 

 interrenal tissue is also in doubt, since they appear to arise from 

 the pro- and meso-nephric ducts, and not from coelomic epithe- 

 lium (cf. Pickford and Atz, 1957). 



2.312 Adrenal cortex 



Like the interrenal tissue, the adrenal cortex is a small mass of 

 conspicuous yellow tissue ; but it is paired and situated in front of, 

 or below, the kidneys, w^hether these are mesonephric or meta- 

 nephric. The colour is due to large amounts of fat enclosed in the 

 cells and associated with the formation of the sterolic hormones 

 secreted by the gland. The presence of stored hormone in the 

 gland is also related to the presence of ascorbic acid, which becomes 

 depleted when the hormone is passed into the blood stream in 

 response to some form of stress (§ 4.231 and Fig. 4-9), and to 

 release of ACTH. 



Three layers can usually be recognised in the cortex : an outer 

 layer (just within the connective tissue capsule enclosing the whole 

 gland), where active cell multiplication follows the frequent nuclear 

 mitoses ; a thicker middle region of actively secreting cells ; and the 

 innermost layer, next to the medulla, where the cells become 

 degenerate and are eventually consumed by macrophages from the 

 blood. It seems that throughout the life of the gland, cells are 

 formed near the outer surface, migrate inwards during their 

 secretory phase and are then destroyed as they reach the inner 

 surface. 



The main secreting cells of the cortex form a compact mass or 

 continuum, in which the individual cells tend to be polyhedral, 

 from contact with adjacent cells (Fig. 2-14c). In the rat, the mass 

 is tunnelled through by a network of blood sinusoids, so abundant 

 that every cell has a facet in contact with a blood vessel into which 

 its secretion can be passed (Pauly, 1957; Fig. 2-15). 



The structural details of the gland, and the proportion of 

 connective tissue to gland cells, varies from species to species; 

 but this has not been shown to have any effect upon the functional 

 activity of the gland. No nerves have been detected. 



