- The adrenal glands are small, triangular-shaped endocrine organs located on top of each kidney. Despite their relatively small size—typically measuring about 5 cm in length and weighing around 4–5 grams each—they play a vital role in maintaining homeostasis through the production of several essential hormones.
- Each adrenal gland is composed of two anatomically and functionally distinct regions: the outer adrenal cortex and the inner adrenal medulla. These two regions originate from different embryological tissues and produce different types of hormones, which affect a wide range of physiological functions.
- The adrenal cortex, derived from mesodermal tissue, is further divided into three zones: the zona glomerulosa, zona fasciculata, and zona reticularis. Each of these zones produces specific steroid hormones. The zona glomerulosa secretes mineralocorticoids, primarily aldosterone, which regulate sodium and potassium balance and, consequently, blood pressure. The zona fasciculata produces glucocorticoids, especially cortisol, which are crucial in the body’s response to stress, metabolism regulation, and immune modulation. The innermost layer, the zona reticularis, synthesizes androgens, such as dehydroepiandrosterone (DHEA), which contribute to the development of secondary sex characteristics and may have various roles in both sexes.
- In contrast, the adrenal medulla, which originates from neural crest cells, functions as part of the sympathetic nervous system. It secretes catecholamines—mainly adrenaline (epinephrine) and noradrenaline (norepinephrine)—in response to stress. These hormones prepare the body for the “fight or flight” response by increasing heart rate, expanding air passages in the lungs, mobilizing energy stores, and redirecting blood flow to essential organs such as the heart and muscles. This rapid response system allows the body to react quickly to emergencies and stressors.
- Together, the adrenal cortex and medulla form a sophisticated system that integrates hormonal and neural signals to help the body maintain fluid balance, respond to stress, regulate metabolism, and manage immune responses. Disorders of the adrenal glands, such as Addison’s disease, Cushing’s syndrome, pheochromocytoma, or congenital adrenal hyperplasia, can lead to significant health issues due to hormone imbalance. Understanding adrenal gland function is therefore critical in endocrinology and internal medicine.
