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Pharyngeal Endoderm Fates


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What are the 3 fates of pharyngeal endoderm?
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?
-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?
What is cretinism?
3 symptoms:
Form of dwarfism
-Mental retardation
-Growth retardation
-Dry skin
What 2 conditions can develop from a Persistent Thyroglossal Duct?
What is the main difference between a cyst and fistula?
Cysts - not usually open

Fistula - sinuses which are the result of a ruptured cyst.
What is a Persistent Thyroglossal Duct Cyst?
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:
-Retains connection to pharynx
-Becomes auditory tube, middle ear cavity
Fate of 2nd Pharyngeal Pouch:
Palatine tonsil
Fate of 3rd Pharyngeal Pouch:
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?
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.

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