Pharyngeal Pouch (Embryology)

Pharyngeal Pouch General Facts:

• Also known as branchial pouches.
• 6 Pouches altogether.
• Important in the development of vertebrate animals.
• Form on the endodermal side between the branchial arches.
• Pharyngeal clefts (or grooves) form the lateral ectodermal surface of the neck region so separating the arches.
• All the pouches line up with their respective clefts.
• The thin segments between the pouches become gills in fish.

First Pouch:

• The endoderm lines the following future structures - auditory tube, middle ear, mastoid antrum, & inner layer of the tympanic membrane.
• Also lines the origin of the Mandibular nerve & Maxillary artery.

Second Pouch:

• Contributes to the middle ear, palatine tonsils.
• Supplied by the facial nerve.

Third Pouch:

• This pouch has Dorsal & Ventral wings.
• Products of the dorsal wings include the inferior parathyroid glands.
• The ventral wings fuse to form the cytoreticular cells of the thymus.
• Main nerve supply to the derivatives of this pouch is cranial nerve IX (glossopharyngeal nerve).

Fourth Pouch:

• Produces superior parathyroid glands & ultimobranchial body.
• The ultimobranchial body forms the parafollicular C-Cells of the thyroid gland.
• Also produces the muscles & cartilage of larynx (with the sixth pharyngeal pouch).

Fifth Pouch:

• This is a rudimentary structure.
• Becomes part of the fourth pouch where it contributes to the thyroid C-cells.

Sixth Pouch:

• Together with the fourth pouch, contributes to the formation of the laryngeal musculature & cartilage.

Image Pattern of the Pharyngeal Arches:

• I-IV branchial arches, 1-4 brancial pouches (inside) &/or pharyngeal grooves (outside),
• a - Tuberculum laterale
• b - Tuberculum impar
• c - Foramen cecum
• d - Ductus thyreoglossus
• e - Sinus cervicalis

Image: Pharyngeal Pouches I-IV by Wikipedia User: Uwe Gille (GNU Free Documentation License)

Tags: Embryology - Larynx - Middle Ear - Palatine Tonsils - Parathyroid Gland - Pharyngeal Pouch - Thymus - Thyroid C Cells - Ultimobranchial Body
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