AL2 Development of Endocrine System

• Germinal layers

  • Ectoderm
  • Mesoderm
  • Endoderm
• Development of Pituitary Gland (Hypophysis Cerebri)

  1. Outpocketing of stomodeum immediately in front of buccopharyngeal membrane (Rathke's pouch)

  2. Downward extension of diencephalon (Infundibulum)

  3. Rathke's pouch grows dorsally towards the infundibulum

  4. Rathke's pouch loses connection with oral cavity

  5. Anterior wall of Rathke's pouch increases in size to form adenohypophysis

  6. Extension of anterior lobe along the stalk develops into pars tuberalis

  7. Posterior wall of Rathke's pouch develops into pars intermedia

  8. Infundibulum gives rise to stalk and pars nervosa
• Divisions of the Pituitary Gland

  Adenohypophysis (Pars tuberalis, Pars distalis, Pars intermedia)<|>Neurohypophysis (Infundibular stalk, Pars nervosa, Median eminence)
• Development of Thyroid Gland

  1. Endodermal thickening appears in the midline of the floor of the pharynx

  2. Thickening forms a diverticulum called thyroglossal duct

  3. Duct elongates and forms a bi-lobed solid cell cord at its distal end which expands to form the thyroid gland

  4. Thyroid gland migrates inferiorly in the neck

  5. Gland develops into a small, median isthmus and 2 lateral lobes
• Thyroglossal cyst

  Cysts may occur in the midline at any point along the thyroglossal duct, most commonly below the hyoid bone<|>Cysts develop as a result of persistence of a small amount of epithelium that continues to secrete mucus<|>Cysts are prone to infection and should be removed surgically
• Thyroglossal fistula

  Infection of the thyroglossal cyst may lead to its spontaneous rupture resulting in formation of a sinus or fistula<|>All remnants of thyroglossal duct should be removed surgically
• Agenesis of thyroid

  Failure of development of the thyroid gland<|>Commonest cause of cretinism
• Development of Parathyroid Gland

  1. Pharyngeal arches consist of 4 pairs of bars of mesenchymal tissue separated externally by deep grooves known as pharyngeal clefts

  2. Outpocketings (5 pairs) appear along the lateral walls of the pharyngeal gut (foregut) and are known as pharyngeal pouches
• Superior parathyroids

  4th pharyngeal pouch
• Inferior parathyroids

  3rd pharyngeal pouch
• Suprarenal gland

  Composed of cortex (mesodermal origin) and medulla (ectodermal origin)
• Development of Suprarenal Glands

  1. Mesothelial cells between the root of mesentery and the developing gonad proliferate and penetrate the underlying mesenchyme and differentiate into an acidophilic cell mass known as the primitive cortex (foetal cortex)

  2. Second wave of mesothelial cells then penetrate the mesenchyme and surround the original acidophilic mass

  3. These smaller cells later form the definitive cortex (adult cortex) which surrounds the original acidophilic cell mass (foetal cortex)

  4. The definitive (adult) cortex later forms the ZG and ZF

  5. The foetal cortex that persists will differentiate into reticular zone (ZR)
• Neural crest cells

  Origin of dorsal root ganglion, sympathetic ganglia, and suprarenal gland
• Development of Suprarenal Glands

  1. Cells originating from the sympathetic system invade the medial aspect of the fetal cortex

  2. These cells give rise to the medulla

  3. They stain yellow-brown with chrome salts and are also known as 'chromaffin' cells
• Summary


  • Adrenal cortex has mesodermal origin
  • Adrenal medulla has ectodermal origin
  • Coelomic mesothelium
  • Neural crest cells
• germinal layer and endocrine gland

  1. ectoderm = pituitary, adrenal medulla, pineal
  2. mesoderm = adrenal cortex, gonads
  3. endoderm = thyroid, parathyroid, pancreatic islet, thymus
• gross division of pituitary gland

  1. anterior lobe = pars tuberalis, pars distalis
  2. neural stalk = median eminence, infundibular stalk
  3. posterior lobe = pars intermedia, pars nervosa
• Histological development of thyroid gland

  1. thyroid follicle = Due to invasion by surrounding vascular mesenchymal tissue, the solid mass of thyroid cells broken up into plates, cords and cell clusters called follicles.
  2. colloid = The homogenous eosinophilic gel-like substance starts to accumulate in the center of each follicle by 3rd month
  3. fibrous capsule = develop from the surrounding mesenchyme.
  4. Ultimobranchial bodies (5th pharyngeal pouch) and neural crest cells are incorporated into the thyroid gland to form the parafollicular cells.
• Origin for the Anterior lobe of pituitary glands 


  Rathke's pouch
• Origin for posterior lobe of pituitary glands

  Infundibulum
• Acidophils appear


  red in Mallory stain and contains somatotrophs (secrete somatostatin which stimulated IGF-1) & mammotrophs (secrete prolactin)
• Pituicytes (2 points)*

  1. provide support & nutrition to the axons
  2. contains Herring bodies
• the neurosecretory hormone released in pars nervosa include

  ADH/vasopressin, oxytoxin & neurophsin
• 4 OSPE features in thyroid gland

  1. Capsule
  2. septa
  3. Typical follicle cell
  4. Parafollicular C cell
• Iodine is required for

  formation of thyroxine
• ; iodine deficiency can lead to the


  development of enlarged thyroid goiters
• Parafollicular cell derived from

  Neural crest cell
• effective identification use for thyroid glands

  1. immunohistochemistry
  2. electron microscopy
• OSPE identification for parathyroid gland

  1. Capsule
  2. septa
  3. Chief cell
  4. oxyphil cell
• Adrenal cortex hormone (MCA)


  1, Zone gloMerulosa - Mineralocorticoids

  2, zona fasiCularis - Corticosteroid

  3, zona reticulAris - weak Androgen