Superior adrenal artery, typically arises from the inferior phrenic artery, and rarely from the aorta, celiac axis, or intercostal arteries.
Middle adrenal artery, typically arises from the lateral aspect of the aorta and rarely from the inferior phrenic artery or renal artery.
Inferior adrenal artery typically arises from the superior aspect of the ipsilateral renal artery
The superior arterial supply from the phrenic artery is constant; the middle and inferior arteries are variable
Blood distribution within the adrenal gland
Capsular arteries supply only the adrenal capsule and do not penetrate more deeply into the tissue.
The medulla has two blood supplies
Arterial blood from the medullary arterioles
Medullary arterioles travel within the trabeculae of the adrenal gland to deliver blood to the medullary capillary sinusoids.
Venous blood from the cortical sinusoid capillaries that have already supplied the adrenal cortex with arterial blood
Fenestrated cortical sinusoidal capillaries supply the cortex and then drain into fenestrated medullary capillary sinusoids.
This dual vascular supply is important for the medullary production of catecholamines
As venous blood from the adrenal cortex reaches the medullary tissue, it contains a high concentration of glucocorticoids, and this situation plays a role in epinephrine synthesis
Sympathetic innervation of the adrenal gland causes release of catecholamines from the chromaffin cells of the medulla.
Pre-ganglionic sympathetic nerve fibers from T11-L2 (lower thoracic and lumbar spinal cord) travel through the sympathetic chain to reach a nerve plexus at the adrenal capsule which then traverse the cortex to directly innervate the chromaffin cells of the medulla; there is no post-ganglionic innervation of the medulla
Post-ganglionic fibers originating from the [parasymp vs. symp?] splanchnic ganglia provide innervation to the adrenal cortex
Composed of 2 embryologically and functionally distinct components:
Outer cortex
Makes up ≈90% of the adrenal mass
Endocrine component
Derived from intermediate mesoderm
Composed of 3 layers (from outer to inner):
Zona Glomerulosa
Comprises ≈15% of the cortex
Produces aldosterone as a result of unique zonal expression of aldosterone synthase (CYP11B2)
Zona Fasciculata
Comprises ≈80% of the cortex
Produces glucocorticoids as a result of zonal expression of 17α-hydroxylase, 21-hydroxylase, and 11β-hydroxylase enzymes
Cortisol is the main glucocorticoid
Zona Reticularis
Comprises ≈5-7% of the cortex
Produces the sex hormones as a result of zonal expression of 17α-hydroxylase and 17,20-lyase (3):
Dehydroepiandrosterone (DHEA)
Sulfated DHEA (DHEA-S)
Androstenedione
The sex hormones (DHEA, DHEA-S, and androstenedione) comprise the greatest portion of steroid hormone that is produced by the adrenals (>20 mg/day), but appear to be the least important for adult physiologic homeostasis
Only 100-150 mcg/day of aldosterone and approximately 10-20 mg/day of cortisol are produced by the glands.
Inner medulla
Neurocrine component
Derived from neural crest cells that later give rise to chromaffin cells
Chromaffin cells of the medulla secrete the catecholamines (3):
Epinephrine (80%)
Norepinephrine (19%)
Dopamine (1%)
These catecholamines are produced from the amino acid tyrosine
The adrenal gland is the primary source of systemic epinephrine
Despite the presence of similar chromaffin cells elsewhere in the sympathetic nervous system, the enzyme phenylethanolamine-N-methyltransferase (PNMT), which catalyzes the conversion of norepinephrine to epinephrine, is relatively unique to the adrenal medulla (the brain and organ of Zuckerkandl also express this enzyme)
Adrenal gland anatomy and histology. Source: Wikipedia
