The two adrenal glands are situated next to the kidneys and their main function is to release body regulating chemicals in response to nerve signals generated by the autonomic nervous system (ANS). The Autonomic nervous system regulates automatic bodily functions such as heart beat, automatic breathing, dilation of blood vessels in response to heat and many other functions that we are seldom aware of. The adrenal glands are "plugged into" a sub-division of the ANS called the sympathetic nervous system.
The adrenal glands are organised into an inner medulla and an outer cortex.
The medullae are richly innervated with sympathetic nerve fibres and release regulatory biochemicals in response to sympathetic nervous signals such as emotional excitement, fear, apprehension, psychic distress, panic reactions, sexual activity and fight-or-flight stimuli. These biochemicals are called catecholamines and include epinephrine (adrenaline) and norepinephrine and they prepare many parts of the body for the appropriate responses to such signals.
The cortexes release a class of biochemicals called steroid hormones, in particular glucocorticoids and mineralocorticoids among others. Glucocorticoids play a very important regulatory function and there are few cells in the entire body that do not have glucocortico-receptors. With respect to the immune system, glucocorticoids act as anti-inflammatory and immunosuppressive agents and are widely used in autoimmune diseases including multiple sclerosis.
A hormone reponsible for regulating natural bodily glucocorticoids, adrenocorticotropic hormone (ACTH) used to be used to control MS relapses. Its use has now largely been replaced by synthetic glucocorticoids such as Methylprednisolone.
Adrenal Gland links:
Adrenal Gland: Introduction and Index
The Autonomic Nervous System