The roles of corticosterone

In many species, including amphibians, reptiles, rodents and birds, corticosterone is a main glucocorticoid,[1] involved in regulation of fuel, immune reactions, and stress responses.

However, in humans, corticosterone is produced primarily in the zona fasciculata of the adrenal cortex. It has only weak glucocorticoid and mineralocorticoid potencies in humans and is important mainly as an intermediate in the steroidogenic pathway from pregnenolone to aldosterone. Corticosterone is converted to aldosterone by aldosterone synthase, found only in the mitochondria of glomerulosa cells. Glomerulosa cells are found in the Zona glomerulosa, which is the most superficial region of endocrine cells in the adrenal cortex.

From:http://www.steroid-hormones.com/Cortical-Hormone/11/