(1) Adrenal gland, (2) Left kidney, (3) Abdominal aorta, (4) Inferior phrenic arteries, (5) Superior adrenal arteries, (6) Middle adrenal arteries, (7) Inferior adrenal arteries, (8) Aberrant accessory renal artery, (9) Renal arteries, (10) Testicular arteries
The adrenal glands (Glandulae suprarenales) are paired organs located closely to the upper pole of the kidneys in the retroperitoneal space on both sides.
The right adrenal gland has topographical relations to the liver and the inferior vena cava, while the left is separated from the posterior wall of the stomach by the omental bursa and extends to the spleen. Both adrenal glands are located approximately at the level of the 11th/12th thoracic vertebrae and are surrounded by a vascular connective tissue capsule containing collagen fibers and smooth muscle cells. In adults, the weight of an adrenal gland is about 5-7 grams.
They are flattened in the dorsoventral direction, allowing for the distinction of an anterior and a posterior surface. The left adrenal gland is crescent-shaped, while the right resembles a triangular bishop's hat. The anterior surface of the left adrenal gland has a complete peritoneal covering, whereas the right adrenal gland is only covered by peritoneum in its caudal part. The posterior surface of both adrenal glands rests on the lumbar part of the diaphragm.
The adrenal glands are highly complex, dual-regulated endocrine organs. Their asymmetrical vascular anatomy, the close functional connection between cortex and medulla, and their rich lymphatic and blood supply make them a central element of hormonal and autonomic balance in the human body.
The adrenal glands consist of two distinct parts – the cortex and the medulla. These areas differ in both their embryological origin and function. The adrenal cortex develops from the mesoderm and is histologically divided into three zones: the zona glomerulosa, the zona fasciculata, and the zona reticularis. Each of these layers produces specific hormones. The zona glomerulosa synthesizes mineralocorticoids, particularly aldosterone, which regulates sodium and potassium balance as well as blood pressure. The zona fasciculata primarily produces glucocorticoids, mainly cortisol, which influence carbohydrate and protein metabolism and the stress response. The innermost layer, the zona reticularis, produces androgens to a lesser extent, contributing to the formation of male sex hormones, especially in women.
The adrenal medulla originates from neural crest cells and is functionally associated with the sympathetic nervous system. It consists of so-called chromaffin cells, which synthesize catecholamines adrenaline and noradrenaline and release them during stress situations ("fight-or-flight" response).
The blood supply to the adrenal glands is provided by three arterial sources: the superior adrenal artery (from the inferior phrenic artery), the middle adrenal artery (directly from the abdominal aorta), and the inferior adrenal artery (from the renal artery). Numerous variations exist!
These arteries form a dense network under the capsule, from which capillaries branch into the cortical zones. The venous blood from the cortex then flows through the medulla before being drained by a central vein. This arrangement allows cortical hormones – particularly cortisol – to reach the chromaffin cells of the medulla directly, where they can stimulate adrenaline production.
The venous drainage occurs through a single central vein, the adrenal vein. On the right side, the right adrenal vein is short and drains directly into the inferior vena cava. Due to its short length and thin wall, it is considered particularly vulnerable to injury, for example, during surgical procedures on the right adrenal gland. On the left side, the blood flows through the left adrenal vein, which usually drains together with the left inferior phrenic vein into the left renal vein. The central veins of the adrenal glands have a characteristic spiral smooth muscle, which regulates blood flow and indirectly hormone release.
The lymphatic drainage of the adrenal glands begins in a fine subcapsular capillary network that collects lymph from the cortex and medulla. The lymphatic vessels exiting the adrenal glands predominantly follow the arteries. The primary lymph nodes are the para-aortic and lumbar lymph nodes. Some lymphatic vessels pass through the diaphragm to the posterior mediastinal lymph nodes.
The innervation of the adrenal glands is primarily sympathetic. Preganglionic fibers from the thoracic spinal segments (Th5–L1) terminate directly on the chromaffin cells of the medulla, which thus functionally represent postganglionic neurons. This direct connection between the nervous system and the endocrine organ allows for extremely rapid catecholamine release.
Functionally, the adrenal glands are central organs of hormonal regulation. The cortex is controlled via the hypothalamic-pituitary axis by adrenocorticotropic hormone (ACTH), while the medulla is activated via the sympathetic nervous system. Together, they enable a coordinated adaptation of the organism to stress situations, regulate metabolic processes, water and electrolyte balance, and blood pressure.