Adrenal Glands Anatomy

Study Notes

Adrenal glands are paired organs located near the superior poles of the kidneys, embedded in pararenal adipose tissue and fascia.
They are flattened, half-moon shaped structures, approximately 4-6 cm long, 1-2 cm wide, and 4-6 mm thick in adults.
Each gland weighs about 8 g, but their weight and size vary with age and physiologic condition of the individual.
Adrenal glands are covered by a dense connective tissue capsule that sends thin trabeculae into the gland's parenchyma.

Each gland has two concentric regions: a yellowish adrenal cortex and a reddish-brown central adrenal medulla.
The adrenal cortex and medulla have distinct embryonic origins, functions, and morphologic characteristics that become united during embryonic development.
The cortex arises from mesoderm, while the medulla arises from the neural crest.

The adrenal gland lacks a hilum, and three adrenal arteries penetrate the capsule independently and branch to form a subcapsular arterial plexus.
The plexus gives rise to two groups of arterioles: one for the adrenal cortex and one for the medulla, bypassing the cortex.
Cortical capillaries irrigate endocrine cells of the cortex and then drain into the microvasculature of the medulla.
The adrenal medulla has a dual blood supply: arterial blood from the medullary arterioles and venous blood capillaries of the cortex.
Venous drainage from the glands occurs via the suprarenal veins.

Cells of the adrenal cortex have characteristic features of steroid-secreting cells: acidophilic cytoplasm rich in lipid droplets, with central nuclei.
Ultrastructurally, their cytoplasm shows an exceptionally profuse smooth ER (SER) of interconnected tubules, containing enzymes for cholesterol synthesis and conversion of steroid prohormone pregnenolone into specific active steroid hormones.
Mitochondria are often spherical, with tubular rather than shelf-like cristae, and contain enzymes for converting cholesterol to pregnenolone and for some steps in steroid synthesis.

The adrenal cortex has three concentric zones: zona glomerulosa, zona fasciculata, and zona reticularis.
Each zone has distinct characteristics and produces different classes of steroid hormones.
Zona glomerulosa produces mineralocorticoids, zona fasciculata produces glucocorticoids, and zona reticularis produces adrenal androgens.
The three zones respond differently to ACTH stimulation and have different control mechanisms.

Addison disease or adrenal cortical insufficiency is a disorder, usually autoimmune in origin, which causes degeneration in any layer of adrenal cortex, leading to concomitant loss of glucocorticoids, mineralocorticoids, or androgen production.