Adrenals

The avian adrenal gland plays a central role in homeostasis and is composed of chromaffin and cortical tissues that are variably intermingled. The primary role of its secretory products is to regulate energy flow and partitioning. Catecholamines from the chromaffin tissue largely raise blood glucose for rapid energy expenditure during acute stress, especially during the more commonly described "fight-or-flight" response. By contrast, the corticosteroid secretory products from the cortical tissue control more complex functions. The mineralocorticoids are part of a larger system that regulates salt and water balance. The glucocorticoids are part of a larger system that regulates energy flow and partitioning, especially blood glucose. The effects of corticosteroids are mediated by a complex array of cognate intracellular and membrane receptors and receptor isoforms. In addition, the action of glucocorticoids at the cellular level is modulated by various circulating binding globulins and intracellular enzymes in target cells that degrade and regenerate active corticosteroids at the local level. This chapter focuses on the fundamental regulation of the adrenal tissues and the action of catecholamines and corticosteroids, and how they change over the life-history cycle and life-history stage.