Endocrine Embryology Flashcards
How is the hypothalamus formed
3 primary vesicles form 5 ventricles
Each becomes a specific part of brain
3rd ventricle forms diencephalon which forms
Hypothalamus, thalamus, pituitary and pineal
Formation of infidibulum and rathkes pouch
- 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
Rathkes pouch further growth
- Grows doesally toward infundibulum
- Loses connection to stomodeum
- forms discrete sac
- Lies in close contact with infundibulum
Derivatives of Rathkes
- 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
Derivatives of infundibulum
- Give rise to Neurohypophysis
- Pars nervosa
- Pituitary stalk
- Infudibular recess
- remnant of infundibular lumen
*
- remnant of infundibular lumen
What is the neurohypophysis composed of
Neuroflial cells, and nerve fibers from hypothalamus
Posterior pituitary
Pars nervosa and infundibulum contain
- 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
Pars distalis
- 75% of ant pituitary
- Chromophobes
- Chromophils
- Acidophils
- Somatotrophs
- Lactotrophs
- Basophils
- Gonadotrophs
- Thyrotrophs
- Corticotrophs
- Acidophils
Pars Tuberalis
- Cuboidal cells of unknown function
- Gonadotropin colocalization
Pars intermedia
Rudimentary, migrated cells that secrete Melanocyte-stimulating hormone
4th pouch derivatives
- Superior parathyroid
- dorsal portion
- Ultimopharyngeal body
- Diverticulum from 4th, grows caudal and ventral
- Fate- parafollicular cells
- Secretes calcitonin
Histogenesis of Parathyroid glands
- 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
Development of thyroid
- 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
Where is thyroid located
Just below larynx
How is the thyroid activated and what does it produce
- Activated by TSH
- Produces calcitonin, triiodothyronine (t3) Thyroxin T4
Type of cells in thyroid
- Composed of thyroid follicles
- Folicullar cells
- simple cuboidal epithelium
- Parafollicular cells
- Cuboidal, no contact with colloid material
T3 and T4 action
Increase metabolism and helps growth development
Requires iodine for synthesis
T3 and T4 deficiencies
- Too little iodine - simple goiter
- Too little t3 and t4 hypothyroidism
- too much hyperthyroidism
Calcitonin
- 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
Parathyroid gland location
4 bean shaped glands embedded in fascial sheath of thyroid
Parathyroid cells
- Chief cells
- Secrete parathyroid hormone
- binds osteoblasts to signal production of osteoclast-stimulating factor
- Secrete parathyroid hormone
Formation of primitive cortex
- 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
Definitive cortex formation
- 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
Adrenal medulla formation
- 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
