Endocrine Embryology

Question 1

How is the hypothalamus formed

Answer 1

3 primary vesicles form 5 ventricles

Each becomes a specific part of brain

3rd ventricle forms diencephalon which forms

Hypothalamus, thalamus, pituitary and pineal

Question 2

Formation of infidibulum and rathkes pouch

Answer 2

• A diverticulum called infundibulum is formed
  
  • Extension o f diencephalon
  • grows towards site of embryonic mouth stomodeum
• Simultaneously ectodermal out pocketing called Rathkes pouch is formed by the evangenation at the stomodeum immediately in front of buccopharyngeal membrane

Question 3

Rathkes pouch further growth

Answer 3

• Grows doesally toward infundibulum
• Loses connection to stomodeum
• forms discrete sac
• Lies in close contact with infundibulum

Question 4

Derivatives of Rathkes

Answer 4

• Differentiates into adenohypophysis
• Anterior lobe give rise to
  
  • Pars distalis
  • Pars tuberalis
    
    • Grows along infundibulum and surrounds it
  • Pars intermedia
    
    • Formed from cells on posterior of rathkes pouch

Question 5

Derivatives of infundibulum

Answer 5

• Give rise to Neurohypophysis
  
  • Pars nervosa
  • Pituitary stalk
  • Infudibular recess
    
    • remnant of infundibular lumen
      *

Question 6

What is the neurohypophysis composed of

Answer 6

Neuroflial cells, and nerve fibers from hypothalamus

Question 7

Posterior pituitary

Pars nervosa and infundibulum contain

Answer 7

• Pars nervosa has non-myelinated axons and nerve endings (no secretory cells)
  
  • Terminate at Herring bodies
• Infundibulum contains nreve tracts extending from hypothalamus to pars nervosa

Question 8

Pars distalis

Answer 8

• 75% of ant pituitary
• Chromophobes
• Chromophils
  
  • Acidophils
    
    • Somatotrophs
    • Lactotrophs
  • Basophils
    
    • Gonadotrophs
    • Thyrotrophs
    • Corticotrophs

Question 9

Pars Tuberalis

Answer 9

• Cuboidal cells of unknown function
• Gonadotropin colocalization

Question 10

Pars intermedia

Answer 10

Rudimentary, migrated cells that secrete Melanocyte-stimulating hormone

Question 11

4th pouch derivatives

Answer 11

• Superior parathyroid
  
  • dorsal portion
• Ultimopharyngeal body
  
  • Diverticulum from 4th, grows caudal and ventral
  • Fate- parafollicular cells
  • Secretes calcitonin

Question 12

Histogenesis of Parathyroid glands

Answer 12

• Nodules form on the dorsal aspect of each pouch
• Vascular mesenchyme generates capillaries in nodules
• Chief or principal cells differntiate during embryonic period and regulate fetal calcium metabolism
• Oxiphil cells differntiate 5 to 7 years after birth

Question 13

Development of thyroid

Answer 13

• Thyroid gland primordium appears
• Forms apex of foramen cecum of developing tongue
• Primodium descends through neck at thyroglossal duct
• 2 lobes of the thyroid are connected via an isthmus and continue to descend to final position
  
  • Inferior to the circoid cartilage

Question 14

Where is thyroid located

Answer 14

Just below larynx

Question 15

How is the thyroid activated and what does it produce

Answer 15

• Activated by TSH
• Produces calcitonin, triiodothyronine (t3) Thyroxin T4

Question 16

Type of cells in thyroid

Answer 16

• Composed of thyroid follicles
• Folicullar cells
  
  • simple cuboidal epithelium
• Parafollicular cells
  
  • Cuboidal, no contact with colloid material

Question 17

T3 and T4 action

Answer 17

Increase metabolism and helps growth development

Requires iodine for synthesis

Question 18

T3 and T4 deficiencies

Answer 18

• Too little iodine - simple goiter
• Too little t3 and t4 hypothyroidism
• too much hyperthyroidism

Question 19

Calcitonin

Answer 19

• Secreted by parafollicular cells
• Secreted when blood calcium levels rise
• Lowers blood calcium levels
  
  • Stimulates calcium deposition in bones by inhibiting osteoclast, enhancing osteoblast
• can help certaincases of osteoporosis

Question 20

Parathyroid gland location

Answer 20

4 bean shaped glands embedded in fascial sheath of thyroid

Question 21

Parathyroid cells

Answer 21

• Chief cells
  
  • Secrete parathyroid hormone
    
    • binds osteoblasts to signal production of osteoclast-stimulating factor

Question 22

Formation of primitive cortex

Answer 22

• From mesoderm
• Proliferation begins of mesothelial cells which lie inbetween root of mesentery and developing gonad
• Penetrate underlying mesenchyme
• Differntiate into fetal or primitive cortex

Question 23

Definitive cortex formation

Answer 23

• Second wave of mesothelial cells that penetrate mesenchyme again
• Surround primitive cortex and becomes definoitive cortex
• Fetal cortex regresses rapidly except for the inner most layer which becomes the reticularis

Question 24

Adrenal medulla formation

Answer 24

• Forms from ectoderm layer
• Neural crest cells invade the medial aspect of fetal cortex
• Arrange in cords and clumps
• Creating medulla, consisting of chromaffincells which secrete catecholamines

Question 25

Beginning of pancreas formation

Answer 25

• Dorsal pancreatic bud grows off duaodenum into dorsal mesentery, opposite hepatic diverticulum
• Ventral pancreatic bud grows into ventral messentery, caudal to gall bladder

Question 26

Final development of pancreas

Answer 26

• Dorsal bud gives rise to head, body, tail
• Ventral bud gives rise to hook like uncinate process and main pancreatic duct
• Annular pancreas
  
  • occurs when there are 2 vntral lobes which migrate in opposite directions around the duodenum and may obstruct duodenum