Pharyngeal arches, pouches, and clefts

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Pharyngeal arches, pouches, and clefts


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USMLE® Step 1 questions

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High Yield Notes

13 pages


Pharyngeal arches, pouches, and clefts

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USMLE® Step 1 style questions USMLE

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A 6- year-old girl presents to the office to evaluate dry skin, fatigue, sensitivity to cold, and constipation. The patient’s mother recalls that the patient had surgery to remove a “benign mass” at the base of her tongue three months ago because of trouble swallowing. Which of the following best describes the embryological origin of this mass?  

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Branchial arch derivatives p. 643-643

Branchial cleft derivatives p. 643

Cranial nerves p. 301, 523

branchial arch derivation p. 644

Facial nerve (CN VII) p. 521, 523

branchial arch derivation p. 644

1st branchial arch p. 643

4th--6th branchial arches p. 644

Glossopharyngeal nerve (CN IX) p. 523

branchial arch derivative p. 644

Incus (ossicles)

branchial arch derivative p. 644

Mesoderm p. 504

branchial arches derivation p. 643

2nd branchial arch p. 643

3rd branchial arch p. 643


branchial arch derivation p. 644

Trigeminal nerve (CN V) p. 523

branchial arch derivation p. 644

Vagus nerve (CN X) p. 523

branchial arch derivation p. 644


Early in development, the embryo is a flat, disc-shaped organism made up of three layers of pluripotent cells called germ layers: an inner layer, called endoderm, a central layer, called mesoderm, and an outer layer, called ectoderm.

These three specialized cell layers give rise to all the organs and tissues in the body.

By week 4 of development, the embryo takes on a more recognizably human form—but to be honest, it still looks more like a shrimp than a baby.

At the cranial (head) end of this little shrimp-like creature, a set of structures called the pharyngeal apparatus begins to develop, consisting of pharyngeal arches, clefts, and pouches.

The pharyngeal apparatus starts forming around weeks 4 and 5, when six little bars of mesoderm, the pharyngeal arches, sprout from the primitive pharynx.

The pharyngeal arches develop in a craniocaudal fashion—meaning they form at the head and continue developing towards the tail end of the fetus.

These paired, symmetrical bumps are numbered from 1 to 6—it’s important to note that the fifth arch either never forms, or it quickly regresses, so it doesn’t develop into any structures.

Between the five pharyngeal arches, four pharyngeal clefts form and cover the external part of the corresponding arch with ectoderm cells, while four pharyngeal pouches line the internal part of their corresponding arches with endoderm.

The components of the pharyngeal apparatus develop into various head and neck structures, and sometimes multiple arches join together to give rise to a single structure.

Each pharyngeal arch, with its associated pouch and cleft, carries its own cranial nerve that innervates the structures that develop from that arch.


Pharyngeal arches, pouches, and clefts are structures that develop in the embryonic stage of human development and are involved in the formation of various head and neck structures, including the face and ears. The pharyngeal arches are derived from mesoderm and give rise to many of the bones and muscles in the head and neck. The pharyngeal clefts derive from the ectoderm, forming structures in the ear canals. The pharyngeal pouches arise from endoderm cells, and these form parts of the ears, as well as the early tonsils, and many portions of the parathyroid glands and thyroid.


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