Adrenal gland and paraganglia
General
Embryology


Topic Completed: 1 March 2013

Revised: 19 December 2018

Copyright: (c) 2002-2018, PathologyOutlines.com, Inc.

PubMed Search: Embryology[TIAB] adrenal gland
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Cite this page: Nodar SR. Embryology. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/adrenalembryology.html. Accessed April 24th, 2019.
Definition / general
  • 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

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
  • 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
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)

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