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== 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 β5g''' (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 casesΒ§''' * '''Blood supply is redundant''' === Arterial Supply === * '''<span style="color:#ff0000">Sources (3):''' *# '''<span style="color:#ff0000">Superior adrenal artery, typically arises from the inferior phrenic artery</span>''', and rarely from the aorta, celiac axis, or intercostal arteries. *# '''<span style="color:#ff0000">Middle adrenal artery, typically arises from the lateral aspect of the aorta</span>''' and rarely from the inferior phrenic artery or renal artery. *# '''<span style="color:#ff0000">Inferior adrenal artery typically arises from the</span>''' superior aspect of the '''<span style="color:#ff0000">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 * '''<span style="color:#ff0000">Composed of 2 embryologically and functionally distinct components:''' *# '''<span style="color:#ff0000">Outer cortex''' *#* Makes up β90% of the adrenal mass *#* '''<span style="color:#ff0000">Endocrine component''' *#* Derived from intermediate mesoderm *#* '''<span style="color:#ff0000">Composed of 3 layers (from outer to inner):''' *#*# '''<span style="color:#ff0000">Zona Glomerulosa''' *#*#* Comprises β15% of the cortex *#*#* '''<span style="color:#ff0000">Produces aldosterone</span>''' as a result of unique zonal expression of aldosterone synthase (CYP11B2) *#*# '''<span style="color:#ff0000">Zona Fasciculata''' *#*#* '''Comprises β80% of the cortex''' *#*#* '''<span style="color:#ff0000">Produces glucocorticoids</span>''' as a result of zonal expression of 17Ξ±-hydroxylase, 21-hydroxylase, and 11Ξ²-hydroxylase enzymes *#*#** '''Cortisol is the main glucocorticoid''' *#*# '''<span style="color:#ff0000">Zona Reticularis''' *#*#* Comprises β5-7% of the cortex *#*#* '''<span style="color:#ff0000">Produces the sex hormones</span>''' as a result of zonal expression of 17Ξ±-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. *# '''<span style="color:#ff0000">Inner medulla''' *#* '''<span style="color:#ff0000">Neurocrine component''' *#* Derived from neural crest cells that later give rise to chromaffin cells *#* '''<span style="color:#ff0000">Chromaffin cells of the medulla secrete the catecholamines (3):''' *#*# '''<span style="color:#ff0000">Epinephrine (80%)''' *#*# '''<span style="color:#ff0000">Norepinephrine (19%)''' *#*# '''<span style="color:#ff0000">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) [[File:1818 The Adrenal Glands.jpg|alt=Adrenal gland anatomy and histology. |center|thumb|900x900px|Adrenal gland anatomy and histology. Source: [[commons:File:1818_The_Adrenal_Glands.jpg|Wikipedia]]]] == 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 β€ 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
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