Adrenal gland & paraganglia


Anatomy & embryology-adrenal

Topic Completed: 1 March 2013

Minor changes: 4 July 2020

Copyright: 2002-2021,, Inc.

PubMed Search: Adrenal gland paraganglia anatomy

Severino Rey Nodar, M.D., Ph.D.
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Cite this page: Nodar SR. Anatomy & embryology-adrenal. website. Accessed September 16th, 2021.
Definition / general
  • Also called suprarenal glands
  • Responsible for release of hormones that regulate metabolism, immune system function, salt-water balance in bloodstream; also aid in body's response to stress
  • A composite of two neuroendocrine organs, the adrenal cortex (mesodermal, produces steroid hormones aldosterone, cortisol and testosterone) and adrenal medulla (neuroectodermal, produces catecholamines)

Anatomic features
  • Left and right-sided glands; left gland is crescentic and right gland is pyramidal in adults; each is 5 x 3 x 1 cm
  • On superiomedial kidneys in retroperitoneum
  • Has two main parts: cortex and medulla
  • Normal weight is 4-6 grams each gland after dissection of fat; acute stress reduces lipid content and weight; prolonged stress induces hypertrophy and hyperplasia and increases weight
  • Has complete fibrous capsule, which may merge with capsule of kidney (either gland) and liver (right sided gland)
  • Neonatal gland is dark red-brown due to congestion with no visible medullary tissue
  • Adrenal glands are supplied by aorta, inferior phrenic arteries and renal arteries; are drained by shorter right adrenal vein and longer left adrenal vein
  • Lymphatics only in capsule, not elsewhere

Adrenal cortex
Adrenal medulla
  • Has ellipsoid shape, is gray-tan and < 10% of gland volume (1% in neonates)
  • Is more prominent with cortical atrophy
  • Most of medulla is within head of gland
  • Highly vascularized
  • Is core of the adrenal gland, and is surrounded by adrenal cortex
  • Secretes approximately 20% norepinephrine (noradrenaline) and 80% epinephrine (adrenaline)
  • Its chromaffin cells, named for their characteristic brown color, are body's main source of circulating catecholamines epinephrine and norepinephrine (Wikipedia)
  • Considered a specialized sympathetic ganglion due to innervation by preganglionic nerve fibers
  • Adrenal medulla and cortex have different embryonic origins
  • Adrenal medulla (inner core) originates from neural crest; has large eosinophilic cells mixed with small nodules of primitive neuroblastic cells; represents 75% of cortical volume at birth, but then involutes due to apoptosis with only stroma present by one year; mesenchyme surrounding these cells differentiates to form an outer adrenal cortex, which is later replaced by adult cortex
  • The outer adrenal cortex is derived from mesothelium and is further divided into 3 distinct layers (zona reticularis, zona fasiculata, zona glomerulosa), each with distinct hormonal functions
  • Premature, stillborn and some neonates with in utero stress have microscopic cystic changes in adrenal glands
  • By day 25 of gestation, bilateral adrenal primordium develops as cords of large polyhedral cells in coelomic epithelium medial to mesonephros and urogenital ridge
  • By day 45, adrenal glands enlarge to 1 mg, and primitive sympathetic cells with nerve tracts migrate to form medulla
  • By week 7, paraganglionic cells replicate and differentiate into chromaffin cells; primitive sympathicoblasts form neuroblastic nodules that peak at weeks 17-20 and usually regress; persistent nodules may be confused with small neuroblastomas
  • By week 8, each gland weighs 4 mg, with outer (definitive) cortex distinct from inner (fetal) cortex
  • From week 8-9, adrenal cortex synthesizes cortisol and is maximal at 8-9 weeks post conception under the regulation of ACTH (also stimulates androstenedione and testosterone secretion)
  • Fetal adrenal gland is relatively large: at week 18, is 4x kidney, but at birth, weighs 5 grams and is only 1/3 size of kidney due to rapid regression of inner cortex
  • At age 1 year, almost completely disappears, but by age 4-5 years, the permanent adult-type adrenal cortex has fully developed
  • References: Endocr Rev 2011;32:317, Endocr Dev 2008;13:19, Endocr Res 1998;24:919
Anatomic anomalies
  • Agenesis of an adrenal gland is usually associated with ipsilateral agenesis of kidney
  • Fused adrenal glands (2 glands join across midline posterior to aorta) are also associated with a fused kidney
  • Adrenal hypoplasia occurs as hypoplasia / absence of fetal cortex with a poorly formed medulla or as disorganized fetal cortex and medulla with no permanent cortex present
  • Adrenal heterotopia describes a normal adrenal gland in an abnormal location
  • Congenital Adrenal Hyperplasia is a family of inherited disorders of adrenal steroidogenesis enzymes which impairs cortisol production by adrenal cortex
Placenta and adrenal gland pathophysiology
  • Placenta and fetal adrenal work together to meet fetal steroidogenic needs
  • Placenta makes progesterone, which fetal cortex converts to cortisol, which triggers type II cell development and surfactant production in lungs
  • Fetal adrenal supplies substrates for placental estrogen synthesis
  • After birth, placental connection is lost, and childs adrenal becomes more like adult adrenal
Diagrams / tables

Images hosted on other servers:

View from front

View from behind

Microscopic (histologic) images

Contributed by Dr. Grigory Demyashkin, I. M. Sechenov First
Moscow State Medical University (Russia) - 6 - 8 week embryo:

Left: metanephros; right: adrenal gland medulla

Left: metanephros; right: adrenal gland medulla

Center: adrenal gland, medulla & final kidney (metanephros)

Images hosted on other servers:

Normal adrenal gland

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