Podcast
Questions and Answers
What do the outer layer of the tympanic membrane and the external auditory meatus derive from?
What do the outer layer of the tympanic membrane and the external auditory meatus derive from?
- First pharyngeal cleft (correct)
- Third pharyngeal pouch
- Fourth pharyngeal pouch
- Second pharyngeal cleft
What anomaly results from the failure of obliteration of the cervical sinus?
What anomaly results from the failure of obliteration of the cervical sinus?
- Branchial cyst (correct)
- Cervical sinus
- Branchial fistula
- Branchial sinus
Which structure is formed from the third pharyngeal pouch?
Which structure is formed from the third pharyngeal pouch?
- Eustachian tube
- Palatine tonsils
- Skeletal muscle
- Thymus gland (correct)
What is the main component found in the mesoderm of each pharyngeal arch?
What is the main component found in the mesoderm of each pharyngeal arch?
What do the second, third, and fourth clefts contribute to?
What do the second, third, and fourth clefts contribute to?
From which source does the ultimo-branchial body originate?
From which source does the ultimo-branchial body originate?
What occurs if a branchial cyst ruptures on the surface?
What occurs if a branchial cyst ruptures on the surface?
Which structure does not arise from the pharyngeal pouches?
Which structure does not arise from the pharyngeal pouches?
Flashcards
Pharyngeal Arches
Pharyngeal Arches
Cylindrical elevations formed from mesoderm on the lateral wall of the pharynx during early embryogenesis.
Pharyngeal Clefts
Pharyngeal Clefts
Four pairs of ectodermal grooves on the external surface of the pharynx. They correspond to pharyngeal pouches internally.
Pharyngeal Pouches
Pharyngeal Pouches
Five pairs of endodermal grooves on the internal surface of the pharynx. They correspond to pharyngeal clefts externally.
First Pharyngeal Cleft Derivative
First Pharyngeal Cleft Derivative
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Second, Third, and Fourth Pharyngeal Cleft Derivatives
Second, Third, and Fourth Pharyngeal Cleft Derivatives
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Branchial Cyst
Branchial Cyst
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Branchial Sinus
Branchial Sinus
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Branchial Fistula
Branchial Fistula
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Study Notes
Pharyngeal Arches
- Pharyngeal arches are six cylindrical elevations formed from the mesoderm of the lateral pharyngeal wall.
- Each arch has an outer ectodermal covering, an inner endodermal lining, and a mesodermal core.
- Four pairs of ectodermal pharyngeal clefts appear externally, and five pairs of endodermal pharyngeal pouches appear internally.
- These clefts and pouches meet closely, corresponding in position.
Branchial Arch Derivatives (Ectoderm)
- First Cleft: Forms the external auditory meatus and part of the tympanic membrane.
- Second, Third, and Fourth Clefts: The mesoderm of the arches pushes the overlying ectoderm, burying these clefts.
- This results in (potential) cervical sinus cavities which disappear completely, often causing anomalies like branchial cysts, sinuses, or fistulas.
Branchial Arch Derivatives (Endoderm)
- First Pouch: Develops into the Eustachian tube, middle ear cavity, mastoid antrum, and the inner ear drum.
- Second Pouch: Develops into the palatine tonsils.
- Third Pouch: Results in the thymus gland and inferior parathyroid glands.
- Fourth Pouch: Develops into the superior parathyroid glands.
- Fifth Pouch: Forms the ultimo-branchial body, incorporating into the thyroid gland later.
Mesodermal Derivatives of the Arches
- First Arch: Includes Meckel's cartilage (part of the mandible), malleus and incus, sphenomandibular ligament, muscles of mastication (temporalis, masseter, medial and lateral pterygoids, mylohyoid, and the anterior belly of the digastric), and mandibular nerve.
- Second Arch: Develops into the stapes, part of the hyoid bone (lesser horn and upper body), stylohyoid ligament, muscles of the face and posterior belly of digastric, and the facial nerve.
- Third Arch: Forms the greater horn and lower part of the hyoid bone, along with the stylopharyngeus muscle, and the glossopharyngeal nerve
- Fourth Arch: Forms the thyroid cartilage, cricothyroid muscle, and the superior laryngeal nerve.
- Fifth Arch: This arch degenerates.
- Sixth Arch: Includes all laryngeal cartilages (except thyroid) and muscles (except cricothyroid). Recurrent laryngeal nerve.
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