Makindo Medical Notes

Related Subjects: |Embryology Heart and Fetal circulation |Embryology Pharyngeal arch derivatives |Embryology of Nervous system |Embryology of Organ Development |Embryology of Blood and Immune System |Embryology of Limb Development

Pharyngeal Structures

• 5 Arches: Arches 1, 2, 3, 4, and 6 (Arch 5 is rudimentary and disappears): Derived from mesoderm.
• 4 Pouches: Pouches 1, 2, 3, and 4: Derived from endoderm.
• 4 Clefts: Clefts 1, 2, 3, and 4: Derived from ectoderm.

Pharyngeal Arch 1

• Cartilage (Meckel's Cartilage): Mandible, malleus, incus, sphenomandibular ligament.
• Muscles: Muscles of mastication (masseter, temporalis, medial and lateral pterygoid), tensor tympani, tensor veli palatini, mylohyoid, anterior belly of the digastric.
• Nerve: Mandibular branch of Trigeminal Nerve (Cranial Nerve V).

Pharyngeal Arch 2

• Cartilage (Reichert's Cartilage): Stapes, styloid process, lesser horn of the hyoid bone, stylohyoid ligament.
• Muscles: Muscles of facial expression, stapedius, stylohyoid, posterior belly of the digastric.
• Nerve: Facial Nerve (Cranial Nerve VII).

Pharyngeal Arch 3

• Cartilage: Greater horn of the hyoid bone.
• Muscle: Stylopharyngeus.
• Nerve: Glossopharyngeal Nerve (Cranial Nerve IX).

Pharyngeal Arch 4 to 6

• Cartilages: Laryngeal cartilages (thyroid, cricoid, arytenoid, corniculate, cuneiform).
• Muscles:
  • 4th Arch: Pharyngeal constrictors, cricothyroid, levator veli palatini (related to swallowing and speech).
  • 6th Arch: Intrinsic muscles of the larynx (except cricothyroid), important for vocal cord movement.
• Nerve:
  • 4th Arch: Superior laryngeal branch of Vagus Nerve (Cranial Nerve X).
  • 6th Arch: Recurrent laryngeal branch of Vagus Nerve (Cranial Nerve X).

Clefts

• 1st Cleft: Forms the external auditory meatus and contributes to the external surface of the tympanic membrane.
• 2nd - 4th Clefts: Temporary structures that form cervical sinuses, which normally obliterate during development. If not obliterated, they may form branchial cleft cysts.

Pharyngeal Pouch Derivatives

• 1st Pouch: Forms the middle ear cavity, Eustachian tube, and mastoid air cells.
• 2nd Pouch: Contributes to the epithelium of the palatine tonsils.
• 3rd Pouch: Develops into the inferior parathyroid glands and the thymus.
• 4th Pouch: Forms the superior parathyroid glands and contributes to the formation of the thyroid gland.

Conclusion

Understanding the development and derivatives of the pharyngeal arches, pouches, and clefts is crucial in the field of embryology and clinical medicine. Abnormalities in these structures can lead to various congenital anomalies and syndromes. Comprehensive knowledge of these embryological structures aids in the diagnosis and management of related medical conditions.

References

• Embryology Reference. Pharyngeal Arch Structures. Available at: https://www.makindo.co.uk
• Medical Textbook. Development of the Pharyngeal Arches. Available at: https://www.makindo.co.uk
• Clinical Embryology. Pharyngeal Clefts and Pouches. Available at: https://www.ncbi.nlm.nih.gov
• Gray's Anatomy. Head and Neck Anatomy. Available at: https://www.ncbi.nlm.nih.gov