Head and Neck: Embryology of the Midline Structures Flashcards
What is the infundibulum?
A downwards outgrowth of the forebrain that grows to make contact with the developing pharynx at Rathke’s pouch
What is Rathke’s pouch?
What is its clinical significance?
An out pocketing of the ectoderm of the stomatodeum which is an invagination of the roof of the oropharynx. It grows towards the developing forebrain to meet the infundibulum
If it does not regress there can be Rathke’s pouch cysts in the anterior pituitary
What does the infundibulum and Rathkes pouch form?
Rathkes pouch pinches off from the face to form the anterior pituitary
The Infundibulum forms the stalk and the posterior pituitary
How is the tongue attached to the floor of the mouth?
Via the lingual frenulum (can be congenitally short which limits mobility of the tongue)
What is the foramen cecum and sulcus terminalis?
The sulcus terminalis is the border between the anterior 2/3rds and posterior 1/3rd of the tongue
The foramen cecum is at the centre of the sulcus terminalis and is the landmark of the upper end of the thyroglossal duct
Which pharyngeal arches is the tongue formed from?
Has contributions from all of them
Arch 1: 2 lateral lingual swelling and the tuberculum impar
Cupola formed from arch 2,3 and 4
arch 4: epiglottal swelling
(look at an image)
How does the tongue go from being derived from all the arches and adhered to the floor to a mobile tongue?
Lateral lingual swelling overgrow the tuberculum impar
Extensive degeneration (apoptosis) occurs to free the longue from the floor of the oral cavity, just leaving the lingual frenulum
What is the initial and final position of the thyroid gland?
Primordia of the thyroid begins in the floor of the pharynx between the tuberculum impar and the cupola.
The final position is in the anterior neck
Describe the descent of the thyroid
Origin of the descent is later marked at the foramen cecum
It bifurcates and descends as a bi-lobed diverticulum. It remains connected to the tongue via the thyroglossal duct which remains patent in 50% of the population.
Migrates anterior to the pharyngeal gut, hyoid bone and laryngeal cartilages
What are the contents of the thyroid?
Where are they derived from?
Follicular cells (make thyroxin and triidothyronine) - formed from the thyroid diverticulum
Parafollicular C cells (make calcitonin) - formed from the ultimobranchial body of the 4th Ph pouch
Where can ectopic thyroid tissue be present?
Anywhere along the route of the thyroid descent
What are thyroglossal cysts and fistulae?
If the duct remains patent the duct can connect to the surface causing a fistulae.
Thyroglossal cysts can form anywhere along the descent but branchial cysts will be on the border of SCD
What is first arch syndrome?
Give an example?
Defects in the development of the eyes, ears, mandible and palate due to failure of neural crest cells to colonise the first arch.
Treacher-Collins syndrome is an example - characterised by hypoplasia of the mandible and facial bones, abnormal pinna
What is di-george syndrome?
Abnormal development of the neural crest causing thymic aplasia and absence of parathyroid glands.
Use CATCH22 C-cardiac abnormalities esp ToF A-abnormal facies T-thyroid aplasia C-cleft palate H-hypocalcaemia 22- deletion on chromosome 22
What is CHARGE syndrome?
A mutation in CHD7 which is essential for production of the multipotent neural crest
C-coloboma (madelaine mcann eye)
H-heart defects
A-choanal Atresia (nasal passage blocked)
R-retardation
G-genital hypoplasia
E-ear defects
