The adrenal medulla is the inner region of the adrenal gland, a small, triangular organ positioned on top of each kidney. This glandular tissue serves as a direct connection between the body’s endocrine system and its nervous system. It plays a role in regulating involuntary bodily functions, such as heart rate. The adrenal medulla acts as a swift response unit, preparing the body for immediate demands.
Hormones of the Adrenal Medulla
The adrenal medulla produces and releases hormones known as catecholamines, primarily epinephrine (also called adrenaline) and norepinephrine (also called noradrenaline). These hormones are derived from the amino acid tyrosine and are secreted directly into the bloodstream. Epinephrine affects the body by delivering extra oxygen to muscles, increasing blood pressure, and boosting heart output. Norepinephrine works alongside epinephrine to increase heart rate and blood output, also raising blood pressure through vasoconstriction. Both hormones contribute to glucose metabolism, increasing blood sugar levels for energy.
The Fight-or-Flight Response
When the body perceives a threat, the sympathetic nervous system rapidly signals the adrenal medulla. This activation prompts the chromaffin cells within the medulla to release large amounts of epinephrine and norepinephrine into the circulation. This immediate hormonal surge initiates a coordinated cascade of physiological changes across multiple organ systems. For example, heart rate and the force of heart contractions increase significantly, allowing more blood to be pumped throughout the body. Blood flow is redirected, prioritizing muscles and the brain to enhance physical and mental readiness, while reducing flow to less immediate functions like digestion.
The body also prepares for rapid energy expenditure by breaking down glycogen into glucose, which provides quick fuel for muscles. Concurrently, the respiratory rate increases, and bronchioles in the lungs dilate, allowing for greater oxygen intake. These responses, like heightened awareness and a sudden surge of energy, are characteristic of this systemic preparation. These integrated actions serve to enhance strength, speed, and awareness, enabling a rapid response to perceived danger.
Conditions Affecting the Adrenal Medulla
Dysfunction of the adrenal medulla can lead to specific medical conditions, with pheochromocytoma being the most recognized. This is a rare tumor that forms in the adrenal medulla, causing an overproduction of catecholamines. Symptoms include sudden episodes of severe headache, profuse sweating, heart palpitations, and extremely high blood pressure. These episodes, sometimes described as an “adrenaline rush,” can occur spontaneously or be triggered by physical activity.
Diagnosis involves measuring catecholamine levels and their metabolites in blood or a 24-hour urine collection. Imaging tests, such as CT scans or MRIs, help locate the tumor. Treatment begins with medication, such as alpha-blockers, to control blood pressure and heart rate before surgery. Surgical removal of the tumor is the preferred approach, leading to symptom resolution. Adrenal medullary hyperplasia, a rare benign enlargement of the adrenal medulla, can also cause symptoms of catecholamine excess, similar to pheochromocytoma.