THE ADRENAL GLANDS

KEY POINTS: THE ADRENAL GLANDS

▪ Embryologically the adrenals are distinct from the kidney. Developmental abnormalities of one do not affect the other. ▪ The adrenal is divided into the medulla and the cortex. ▪ The adrenal medulla receives preganglionic sympathetic input that stimulates the release of catecholamines from medullary chromaffin cells. ▪ The adrenal cortex is composed of three distinct areas: the zona glomerulosa, zona fasciculata, and zona reticularis. ▪ Arterial supply to the adrenal comes from branches of the inferior phrenic artery, aorta, and renal artery. ▪ Venous drainage of the adrenal varies by side, with the right adrenal vein directly entering the IVC and the left adrenal vein draining into the left renal vein.

Figure 1-19 A, Right adrenal gland dissected. The inferior vena cava has been excised to fully expose the gland. The celiac arterial trunk, its branches, and associated autonomic nervous plexus are also well demonstrated. B, 1, Inferior vena cava (cut). 2, Right inferior phrenic vein. 3, Right phrenic nerve. 4, Superior adrenal arteries (branching from right inferior phrenic artery). 5, Diaphragm. 6, Inferior phrenic ganglion. 7, Right adrenal gland. 8, Right adrenal vein (cut). 9, Pararenal retroperitoneal fat. 10, Autonomic nerves to adrenal gland. 11, Middle adrenal artery (from aorta). 12, Inferior adrenal artery (from renal artery). 13, Right kidney. 14, Branch of right renal artery. 15, Celiac ganglion. 16, Common hepatic artery. 17, Celiac autonomic nervous plexus. 18, Superior mesenteric artery. 19, Esophagus (cut). 20, Branch of phrenic nerve. 21, Upper pointer, right crus of diaphragm; lower pointer, vagus nerve. 22, Right inferior phrenic artery. 23, Upper pointer, left gastric artery; lower pointer, superior extension of celiac autonomic nervous plexus. 24, Left inferior phrenic artery. 25, Left adrenal gland. 26, Splenic artery. 27, Left adrenal vein. C, Left adrenal gland dissected. D, 1, Inferior vena cava. 2, Esophageal hiatus. 3, Vagus nerve. 4, Right inferior phrenic artery. 5, Left gastric artery. 6, Right celiac ganglion. 7, Celiac artery. 8, Left celiac ganglion. 9, Superior mesenteric artery. 10, Left renal vein. 11, Renal hilar lymph node. 12, Renal autonomic nervous plexus. 13, Esophagus (cut). 14, Peritoneum (cut). 15, Diaphragm. 16, Phrenic autonomic nervous plexus. 17, Upper pointer, superior adrenal arteries (from inferior phrenic artery); lower pointer, superior margin of left adrenal gland. 18, Perinephric fat. 19, Upper pointer, left inferior phrenic artery; lower pointer, medial margin of left adrenal gland. 20, Left adrenal gland. 21, Left adrenal vein. 22, Inferior adrenal artery (in this case branching from perinephric/capsular artery of kidney). 23, Middle adrenal arteries (from aorta). 24, Perinephric blood vessels within Gerota's fascia. 25, Inferior adrenal artery (from renal artery). 26, Perinephric fat. 27, Branch of left renal artery. 28, Left kidney. (A to D, Reproduced from the Bassett anatomic collection, with permission granted by Dr. Robert A. Chase.)

Anatomic Relationships

The adult adrenal glands are 3 to 5 cm in greatest transverse dimension and weigh approximately 5 g. Grossly, they are yellow-orange and noticeably more orange than the surrounding adipose tissue. The position of this bilateral gland varies from right to left, but both glands are enclosed within the perirenal (Gerota's) fascia and are separated from the upper pole of the kidneys by a layer of connective tissue.

The right gland is more superiorly located in the retroperitoneum and is pyramidal. It is almost directly cranial to the upper pole of the right kidney. Surrounding structures include the liver anterolaterally, the duodenum anteromedially, and the inferior vena cava medially. It is also important to note that there is often a retrocaval extension of one wing. The left gland is more crescenteric and medial to the upper pole of the left kidney. The upper and anterior aspects are related to the stomach, tail of the pancreas, and splenic vessels.

Composition

Embryologically, the adrenal is distinct from the kidney. Thus, in cases of renal ectopia, the adrenal gland is not affected. Histologically, the adrenal is divided into two components: the centrally located medulla and the peripherally located cortex ( Fig. 1-20 ). The medulla itself is composed of chromaffin cells derived from neural crest origin. These chromaffin cells are innervated directly by presynaptic sympathetic fibers traveling to the adrenal gland from the sympathetic chains. The secretion of neuroactive catecholamines by the adrenal medulla is thus under sympathetic control.

Figure 1-20 Microscopic section of the adrenal gland showing the adrenal medulla and cortex. The three cortical layers are visible: zona glomerulosa (ZG), zona fasciculata (ZF), and zona reticularis (ZR). (Courtesy of Dr. Hossein Saboorian.)

The adrenal cortex is of mesodermal origin and makes up approximately 90% of the adrenal mass. It is composed of three layers, from external to internal, the zona glomerulosa, zona fasciculata, and zona reticularis. Each layer has a different function, with the glomerulosa producing mineralocorticoids (e.g., aldosterone), the fasciculata producing glucocorticoids (e.g., cortisol), and the reticularis synthesizing sex steroids (androgens).

Adrenal Vessels

The arterial supply to the adrenal gland originates from three sources ( Fig. 1-21 ). Superiorly, branches from the inferior phrenic artery feed the adrenal, while middle branches originate directly from the aorta. Finally, branches from the ipsilateral renal artery supply the adrenal gland. The venous drainage varies by side, although both adrenal glands are drained by a single large vein that exits anteromedially. On the left side this vein joins with the inferior phrenic vein and enters the cranial aspect of the left renal vein. On the right side, the adrenal vein enters the IVC directly on its posterolateral aspect. The lymphatic drainage of the adrenals follows the course of these veins and empties into para-aortic lymph nodes.

Figure 1-21 Arterial supply to the adrenal glands. (From Drake RL, Vogl W, Mitchell AWM: Gray's Anatomy for Students. Philadelphia, Elsevier, 2005, p 329.)