The subcellular morphology of avian adrenal medulla

Abstract

The electron microscopic study of the avian adrenal medulla have shown that in most birds, the epinephrine and norepinephrine cells can be differentiated based on the morphology, size, opacity and the fine structures of their granules. However, the functional characterization of some medullary cells, other than epinephrine and norepinephrine remains unresolved to this date. Among the avian adrenals studied, it is only in the domestic fowl that the separate cellular origin of epinephrine and norepinephrine cells have been established. Earlier studies on the manner of release of secretory granules from the adrenal catecholamine storing cells in birds have led one to infer that exocytosis is only mode of discharge of granules. Surprisingly this is not apparent in some of the reports obtained in recent years. Hence the release mechanism of the adrenomedullary hormones need to be further explored ultrastructurally.