Adrenal Medulla
The adrenal medulla is the inner part of the adrenal gland. It makes up approximately 20% of the gland and is derived from neural ectoderm. It is a highly modified sympathetic ganglion. The cells of the adrenal medulla are called chromaffin cells, which are essentially modified postganglionic sympathetic neurons. The adrenal medulla secretes epinephrine and norepinephrine. These hormones are catecholamines.
Hormones
- Epinephrine (80% of secretion).
- Norepinephrine (20% of secretion).
Physiological Effects of Adrenal Medulla Hormones
The effects of epinephrine and norepinephrine are similar to the effects of sympathetic nervous system activation, but the hormonal effects last longer. The effects of epinephrine and norepinephrine take seconds to manifest.
- "Fight or flight" response: The body responds to fear, extreme stress, and intense exercise with massive activation of the sympathetic nervous system, including the adrenal medulla. This is the "fight or flight" response.
- Increase plasma glucose levels.
- Increase cardiovascular function:
- Increase heart rate.
- Increase blood pressure via vasoconstriction.
- Increase vasodilation in heart vessels.
- Increase lipid breakdown.
- Increase bronchial dilation.
- Decrease gastrointestinal activity.
- Muscle glycogen is converted into glucose for rapid energy.