406 



HISTOLOGY 



the suprarenal gland, do not appear like nerve cells and may be radically 

 different from them, although always closely associated with the sympa- 

 thetic ganglia. Because of their affinity for chromium they are known 

 as chromaffin cells. They produce the important internal secretion, 

 adrenalin, which on injection causes contraction of the musculature of 

 the blood vessels, with consequent rise in blood pressure. The chromamn 

 cells are not confined to the suprarenal glands, as already stated (p. 152). 

 In embryos of 15-20 mm., strands of chromamn cells are seen penetrating 

 the cortical portion of the gland, but it is not until much later that they 

 gather in a central mass which constitutes the medulla; even at 190 mm. 



the invasion is not complete 

 (Zuckerkandl) . As a whole, the 

 gland acquires a relatively very 

 great size in embryos. 



From this mode of development, 

 it is seen that islands of medullary 

 substance may occasionally occur in 

 the cortex, and that outlying por- 

 tions of the gland may not contain 

 any medulla. Moreover portions of 

 the gland frequently become de- 

 tached, forming accessory suprarenal 

 glands. These may remain near the 

 main glands or may be carried down, 

 with the descent of the adjacent 

 sexual glands, into the broad liga- 

 ment, or epididymis (cf . Wiesel, Sitzb. 

 kais. Akad. Wiss., Wien, 1899, vol. 

 108, pp. 257-280). Such glands usually consist entirely of cortex, but they may 

 contain medullary substance. Isolated paraganglia, consisting entirely of medullary 

 substance, are not regarded as suprarenal glands. There is no evidence that acces- 

 sory suprarenal glands may arise from the ccelomic epithelium at a distance from the 

 main glands (Zuckerkandl, Keibel and Mall's Human Embryology, vol. 2). 



Adult Structure. The cortical substance may be divided into three 

 layers or zones the zona glomerulosa, zona fasciculata, and zona reticularis 

 (Fig. 420). The zona glomerulosa, found just beneath the capsule, is 

 said to develop between the second and third years after birth, "reaching 

 its characteristic structure only in the later years of childhood." It con- 

 sists of round masses of cells which in man are much like those of the zona 

 fasciculata; in some animals they are distinguished by their columnar shape. 

 The zona fasciculata is composed of cords of rounded or cuboidal cells, 

 containing secretory granules and an abundance of fat vacuoles (Fig. 421). 

 There is no lumen within these cords and they are not surrounded by base- 

 ment membranes. Thin-walled vessels pass between them, sometimes 

 lodged in connective tissue strands proceeding from the capsule. The 



FIG. 419. SECTION OF THE SUPRARENAL GLAND OF AN 

 EMBRYO OF 17 MM. (Wiesel.) 



A, Aorta; R, cortical portion; S, chromaffin tissue 

 penetrating to form the medulla at SB. (From 

 McMurrich's Development of the Human Body.) 



