Page 665 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat
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RepRoductive ` REPRODUCTIVE—EmbRyOlOgy RepRoductive ` REPRODUCTIVE—EmbRyOlOgy SectioN iii 621
Pharyngeal pouch derivatives
POUCH DERIVATIVES NOTES mNEmONIC
1st pharyngeal pouch Middle ear cavity, eustachian 1st pouch contributes to Ear, tonsils, bottom-to-top:
tube, mastoid air cells endoderm-lined structures 1 (ear)
of ear 2 (tonsils)
2nd pharyngeal pouch Epithelial lining of palatine 3 dorsal (bottom for inferior
tonsil parathyroids)
3 ventral (to = thymus)
3rd pharyngeal pouch Dorsal wings inferior 3rd pouch contributes to 3 4 (top = superior
parathyroids structures (thymus, left and parathyroids)
Ventral wings thymus right inferior parathyroids)
3rd-pouch structures end up
below 4th-pouch structures
4th pharyngeal pouch Dorsal wings superior
parathyroids
Ventral wings
ultimopharyngeal body
parafollicular (C) cells of
thyroid
Cleft lip and cleft Distinct, multifactorial etiologies, but often occur together.
palate
Cleft lip Due to failure of fusion of the maxillary and
merged medial nasal processes (formation of
1° palate).
Cleft palate Due to failure of fusion of the two lateral
palatine shelves or failure of fusion of lateral Frontonasal prominence
palatine shelf with the nasal septum and/or Medial nasal prominence
1° palate (formation of 2° palate). Lateral nasal prominence
Intermaxillary segment
Roof of mouth (1° palate)
Nasal septum
Maxillary prominence
Uvula
Palatine shelves (2° palate)
Uvula
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