Pharyngeal Endoderm Fates
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- What are the 3 fates of pharyngeal endoderm?
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1. Salivary glands
2. Thyroid gland
3. Pharyngeal pouches - What tissue type are the salivary glands derived from?
- Ectoderm - from epithelial ectoderm that invaginates into adjacent mesenchyme.
- What is the difference between exocrine and endocrine glands?
- Exocrine retain a connection with surface epithelium
- What 2 types of abnormalities occur with salivary gland devo?
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-Agenesis (rare) - decreased saliva production
-Ranula - enlarged gland due to a nonpatent duct - Where does Thyroid Gland formation begin?
- As a diverticulum between the lingual swellings -> Foramen cecum in adult
- What arches contribute the Thyroid?
- 1 and 2
- What is the thyroglossal Duct?
- What we call the thyroid after the initial diverticulum disconnects from the pharynx and becomes hollow (patent)
- In what direction does the thyroglossal duct displace?
- Caudally - to the neck from the pharynx.
- What happens to the thyroglossal ductal connection from the pharynx to the neck after migration of the bilobed thyroid?
- It disappears.
- What does agenesis of the thyroid lead to?
- Cretinism
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What is cretinism?
3 symptoms: -
Form of dwarfism
-Mental retardation
-Growth retardation
-Dry skin - What 2 conditions can develop from a Persistent Thyroglossal Duct?
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-Cysts
-Fistulas - What is the main difference between a cyst and fistula?
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Cysts - not usually open
Fistula - sinuses which are the result of a ruptured cyst. - What is a Persistent Thyroglossal Duct Cyst?
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A midline cyst occurring anywhere between the tongue and normal thyroid position.
-any age
-not normally open to skin - What is the common name for an aberrant thyroid tissue in the tongue?
- Lingual thyroid
- Where is a lingual thyroid usually located?
- Within the body of the tongue at the foramen cecum.
- Fate of 1st Pharyngeal Pouch:
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-Retains connection to pharynx
-Becomes auditory tube, middle ear cavity - Fate of 2nd Pharyngeal Pouch:
- Palatine tonsil
- Fate of 3rd Pharyngeal Pouch:
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Two Wings:
-Dorsal = inferior parathyroids
-Ventral = Thymus - Fate of 4th Pharyngeal Pouch:
- Superior parathyroids
- Fate of 5th Pharyngeal Pouch:
- Ultimobranchial body; gets infiltrated by neural crest cells; Becomes C Cells of thyroid.
- What is the main thyroid devo defect to remember?
- Di George syndrome
- What are the symptoms of Di George Syndrome?
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Low ears, hypoplastic mandible
Thymic aplasia, hypoparathyroids
Heart defects, cleft palate - What is thought to be the cause of Di George syndrome?
- Insufficient neural crest cell migration.