Editing Adrenals

== Anatomic relationships ==

* Both adrenals are located at the level of the 11th or 12th ribs
** '''Right gland located more superiorly''' than left
*** Recall that right kidney is located more superioly than left
* '''The adrenals are enclosed within the perirenal (Gerota) fascia''' and are completely surrounded by perirenal adipose tissue.
* '''Each gland is separated from the upper pole of the ipsilateral kidney by a thin layer of connective tissue'''
* '''The weight of each gland is ≈5g''' (range 2-6g)
** '''No variation between genders'''
*** Recall that male kidneys are heavier than female
* Adrenal rests are found in proximity to the celiac axis and along the path of gonadal descent.
* Insert figure

== Surgical landmarks ==

* '''Both adrenal glands are in close proximity to the crus of the diaphragm'''
* '''Right gland''' 
** '''Triangular'''
** '''Located nearly directly cranial to the upper pole of the right kidney'''
** '''Adjacent structures include the'''
*** '''Underside of the liver anterolaterally'''
*** '''Duodenum anteromedially'''
*** '''Lateral margin of the inferior vena cava (IVC) medially'''
*** '''Psoas muscle posteriorly'''
* '''Left gland'''
** '''More crecenteric in shape'''
** '''Lateral surface is in contact with the medial aspect of the upper pole of the left kidney'''
** '''The adjacent structures include the'''
*** '''Splenic vessels and body of the pancreas anteriorly'''
*** '''Aorta medially'''
*** '''Psoas muscle posteriorly'''

== Vasculature ==

* '''Unique because''' '''the arterial and venous anatomy is highly variable'''
** '''In laparoscopic adrenalectomy, an adrenal artery is identified in only 1% of cases§'''
* '''Blood supply is redundant'''
* '''Arterial Supply'''
** '''Sources (3):'''
**# '''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'''
* '''Venous Drainage'''
** '''Both adrenal glands are drained by a single central vein that exits the adrenal anteromedially'''
*** '''The right adrenal vein is short and enters the posterior aspect of the IVC.'''
*** '''The left adrenal vein is longer and joins with the inferior phrenic vein and enters the cranial aspect of the left renal vein'''

== Lymphatic Drainage ==

* Right: paracaval lymph nodes
* Left: para-aortic lymph nodes

== Nerve Supply ==

* '''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'''

== Histology of Adrenal Glands ==

* The gland is surrounded by a capsule
* '''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)
*#** Insert figure

== Radiology ==

* US
** More commonly used for differentiating between solid and cystic masses of the adrenal gland.
*** The retroperitoneal adipose tissue can make it difficult to differentiate normal adrenal tissue from the surrounding structures
* '''CT'''
** '''Most widely used imaging modality for imaging the adrenal glands'''
** '''Normal adrenal tissue (including adenoma) has a density of ≤ 10 Hounsfield units (HU) on non-contrast scan'''
* '''MRI'''
** '''Contrast resolution''' with T1-weighted and T2-weighted images '''is superior to that of CT'''

== Questions ==

# What is the typical arterial blood supply to the adrenal glands?
# Where do the adrenal veins drain to?
# What are the 3 zones of the adrenal cortex and what do the secrete?
# Describe the autonomic innervation of the adrenal medulla
# Which enzyme catalyzes the conversion of norepinephrine to epinephrine?
# What are the catecholamines produced by the medulla? From which amino acid are they made?

== Answers ==

# What is the typical arterial blood supply to the adrenal glands?
## Superior adrenal artery arising from the inferior phrenic artery
## Middle adrenal artery arising from the aorta
## Inferior adrenal artery arising from the adrenal artery
# Where do the adrenal veins drain to?
#* Right adrenal: IVC
#* Left adrenal: renal vein
# What are the 3 zones of the adrenal cortex and what do the secrete?
## Glomerulosa: aldosterone
## Fasiculata: cortisol
## Reticularis: sex hormons
# Describe the autonomic innervation of the adrenal medulla
#* Preganglionic sympathetic nerve fibers act directly on the medulla, there are no postganglionic fibers
# Which enzyme catalyzes the conversion of norepinephrine to epinephrine?
#* PNMT (phenylethanolamine-N-methyltransferase)
# What are the catecholamines produced by the medulla? From which amino acid are they made?
#* Dopamine, noepinephrine, epinephrine
#* Tyrosine

== References ==

* Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 64