The adrenal medulla may function in concert with the sympathetic nervous system, or it may function somewhat independently in meeting the homeostatic demands presented by a variety of stressful stimuli. The adrenal medulla and the concept of stress are inextricably intertwined. McCarty, in Encyclopedia of Stress (Second Edition), 2007 Summary and Conclusion Finally, the adrenal medulla has been autologously transplanted into the human brain in an attempt to relieve the symptoms of Parkinson's disease. The phenomena of vesicular uptake and stimulus–secretion coupling have been studies using the adrenal chromaffin cell. The biosynthesis of catecholamines was elucidated in studies utilizing the adrenal medulla. Molecules such as chromogranins and enkephalins have been extracted from the adrenal medulla and studied in detail. For example, the chromaffin vesicle (the secretory vesicle of chromaffin cells) has been characterized down to a relatively precise number of molecules within the vesicle.

The adrenal medulla is not essential for life, but it has proven to be an important model system for neurobiologists. Clinically, this condition accounts for 0.1% of the cases of hypertension. These cells secrete catecholamines into the bloodstream, and have the general effect of preparing the body for “fight or flight.” Diseases of the adrenal medulla are relatively rare the most common is a tumor of chromaffin cells called pheochromocytoma. The parenchyma of the adrenal medulla is composed of chromaffin cells, which are modified postganglionic sympathetic neurons. The adrenal medulla is the central portion of the adrenal gland. Carmichael, in Principles of Medical Biology, 1997 Summary In these ways the adrenal medulla and its hormones really do lie at the interface between hormonal and neural communication.

However, the actions of the medullary hormones are far more rapid and short-lived than those of most hormones. So the adrenal medulla also functions like a conventional endocrine gland. However, the catecholamines of the adrenal medulla are released into blood, rather than a synaptic cleft, and act at sites distant from the site of secretion, by activating specific receptors. So the medulla functions like a modified sympathetic ganglion. The adrenal medulla itself is modified neural tissue and its activity is regulated by a direct neural input. The hormones of the adrenal medulla are the catecholamines, which also function as classical neurotransmitters in the autonomic nervous system. The adrenal medulla is at the interface between the neural and endocrine systems and has features of both. Shern Chew BSc MD FRCP, in The Endocrine System (Second Edition), 2010 Introduction

Medulla of adrenal gland secretes