Figure 3.

Schematic showing distribution of melanocortin receptors and steroidogenic enzymes in the outer adrenal cortex of the rat (cf. Figure 1). This illustrates that cellular interaction appears to be required to explain both the synthesis of aldosterone and its regulation by ACTH, thus requiring modification of the Standard Model of adrenocortical zonation. Vertical arrows indicate potential origins of proliferation and direction of migration of adrenocortical cells. Although the stem cell population is usually held to be in the capsular/subcapsular region, evidence for all of these possible sites for subsequent proliferation has been reported, (see text and Kim and Hammer, 2007; Chang et al., 2013; Freedman et al., 2013).