Overview
- Branchial apparatus (pharyngeal apparatus)
- branchial clefts (branchial grooves)
- derived from ectoderm located between the arches
- branchial arches
- derived from mesoderm (muscles, arteries) and neural crest cells (bones, cartilage)
- each arch is associated with a cranial nerve
- branchial pouches
- branchial clefts (branchial grooves)
- derived from endoderm which line the foregut
Branchial arch innervation
- 1st arch derivatives
- CN V2 and V3: muscles for “chewing”
- 2nd arch derivatives
- CN VII: muscles for “facial expression”
- 3rd arch derivatives
- CN IX
- 4th and 6th arch derivatives
- supplied by CN X: muscles for “swallowing” and “speaking”
- CN V3, VII, IX, and X are both sensory and motor.
- CN V2 is only sensory
Branchial arch derivatives
Branchial pouch derivatives
- 1st pouch
- forms
- epithelial (endoderm derived) lining of middle ear cavity and eustachian tube
- mastoid air cells
- forms
- 2nd pouch
- forms epithelial lining of palatine tonsil
- 3rd pouch
- dorsal wings
- forms inferior parathyroids
- 3rd pouch derivatives end up below the 4th derivatives
- dorsal wings
- 4th pouch dorsal wings
- forms superior parathyroids
- DiGeorge syndrome (22q11 deletion)
- 3rd and 4th pouches fail to differentiate into thymus and parathyroid glands
- Symptoms
- ↓ PTH due to parathyroid aplasia
- tetany due to hypocalcemia
- T cell deficiency due to thymic aplasia
- recurrent viral/fungal infections
- cell mediated immunity still functional and can fight bacterial infections
- congenital heart and great vessel defects
- absent thymic shadow on CXR
- ↓ PTH due to parathyroid aplasia
- MEN 2A
- mutation of germline RET (neural crest cells)
- pheochromocytoma
- parathyroid tumor
- derived from 3rd/4th pharyngeal pouch
- medullary thyroid cancer
- derived from parafollicular cells from the 4th/5th pharyngeal pouch
- mutation of germline RET (neural crest cells)
- NOTE: 5th pouch degenerates during development