Sunday 9 May 2004
adrenal glands, suprarenal glands; adrenals
The zona glomerulosa predominantly releases mineralocorticoids, particularly aldosterone. The zona fasciculata releases corticosteroids, particularly cortisol. The zona reticularis releases sex steroids, predominantly androgens, but also some estrogens.
In the adult, the normal adrenal gland weighs about 4 gm; but with acute stress, lipid depletion may reduce the weight, or prolonged stress, such as dying after a long chronic illness, can induce hypertrophy and hyperplasia of the cortical cells and more than double the weight of the normal gland.
Beneath the capsule of the adrenal is the narrow layer of zona glomerulosa. An equally narrow zona reticularis abuts the medulla. Intervening is the broad zona fasciculata, which makes up about 75% of the total cortex.
The adrenal cortex synthesizes three different types of steroids:
(1) glucocorticoids (principally cortisol), which are synthesized primarily in the zona fasciculata with a small contribution from the zona reticularis;
(2) mineralocorticoids, the most important being aldosterone, which is generated in the zona glomerulosa;
(3) sex steroids (estrogens and androgens), which are produced largely in the zona reticularis.
The adrenal medulla is composed of chromaffin cells, which synthesize and secrete catecholamines, mainly epinephrine. Catecholamines have many effects that allow rapid adaptations to changes in the environment.
Adrenal gland is a composite of two neuroendocrine organs, the adrenal cortex (mesodermal) and adrenal medulla (neuroectodermal).
Left gland is crescentic and right gland is pyramidal in adults. Each is 5 x 3 x 1 cm. Gland has head (medial), body (middle) and tail (lateral)
Normal weight: 4-6 grams each after dissection of fat. Acute stress reduces lipid content and weight. Prolonged stress induces hypertrophy and hyperplasia and increases weight.
Adrenal gland has complete fibrous capsule, which may merge with capsule of kidney (either gland), and liver (right sided gland). Cortex is bright yellow due to lipid; zona reticularis is thinner and darker
Medulla has ellipsoid shape, is gray-tan and < 10% of gland volume (1% in neonates); is more prominent with cortical atrophy; majority of medulla is within head of gland
Neonatal gland is dark red-brown due to congestion, with no visible medullary tissue
- Adrenal glands are supplied by three arteries, drained by shorter right adrenal vein and longer left adrenal vein.
- Lymphatics only in capsule, not elsewhere
- endocrine glands
- endocrine system