Development Of The Midline Structures Flashcards
Where is the pituitary gland derived from?
Ectoderm and neuroectoderm
How does the posterior lobe of the pituitary develop?
Down-growth from the diencephalon forms in the midline, called the infundibulum
The part of the diencephalon from which the infundibulum arises becomes the floor of the hypothalamus
What does the connection between the diencephalon and the infundibulum become?
The pituitary stalk
How does the anterior lobe of the pituitary develop?
Get an out-pocketing of the the ectoderm of the stomatodeum/roof of the oropharynx which grows up and dorsally to meet the infundibulum.
Called Rathke’s pouch
Loses its connection with the roof of the oropharynx and comes to lie anteriorly to the infundibulum and wrap around the pituitary stalk
What can remnants of Rathke’s pouch produce?
Cysts
What is derived from the infundibulum?
Pituitary stalk and posterior pituitary
What is derived from Rathke’s pouch?
Anterior pituitary
Where does the tongue lie?
Partly in the oropharynx and partly in the oral cavity
What marks the boundary between the anterior and posterior thirds?
Foramen cecum - tip of a V
What connects the tongue to the oral cavity floor?
Lingual frenulum
In which week does the tongue start to develop?
Same time as palate begins to form - 4th week
Which pharyngeal arches make up each of the lingual swellings?
2 lateral lingual swellings
-1st Ph arch
3 medial lingual swellings
- tuberculum impar - ph arch 1
- cupola - ph arch 2 and 3 (+4)
- epiglottal swelling - ph arch 4
What are the lingual swellings?
Proliferations of mesenchyme of pharyngeal arches
What happens to the lingual swellings?
Lateral lingual swellings overgrow the tuberculum impar
The third arch component of the cupola overgrown the second arch component
Apoptosis occurs, freeing the tongue from the floor of the oral cavity except for the lingual frenulum
What is tongue tie?
In a newborn when the frenulum is too short
Affects sucking, feeding and speech development
Sensory innervation of the anterior two thirds of the tongue? Which arches is it derived from?
Pharyngeal arches 1 and 3
General sensory is mandibular branch of trigeminal and glossopharyngeal nerve
Innervation of the posterior third of the tongue and which arches is if derived from?
Pharyngeal arch 3
General is glossopharyngeal arch
Special sensory innervation of the tongue? Why?
Chorda tympani of CNVII
Taste buds develop in papillae
Why does the facial nerve pass through the middle ear cavity?
CNVII is a nerve of the second pharyngeal arch
Passes into the first pharyngeal arch so has to go through the first pharyngeal pouch, from which the middle cavity is derived
Where do the intrinsic and extrinsic muscles develop from?
Myogenic precursor cells that migrate into the developing tongue
Innervation of the muscles of the tongue?
Hypoglossal (CNXII)
Except for the palatoglossus - CNX (vagus)
Where does the primordium of the thyroid gland appear?
Floor of the pharynx between the tuberculum impar and the cupola
Appears as an expansion of mesenchyme between the first and second pharyngeal arches and marked in adults by the foramen cecum
Does the thyroid bifurcate before or after its descent?
Before - so travels as a bilobed diverticulum connected by a central isthmus
What keeps the thyroid connected to the tongue after its descent?
Thyroglossal duct
What are the two main cell types of the thyroid and what is their function?
Follicular cells
- thyroxine (T3)
- triiodothyronine (T4)
Parafollicular cells (C-cells) -calcitonin
Where are the two types of thyroid cells formed from?
Follicular
-thyroid diverticulum (first and second pharyngeal arches)
Parafollicular
-ultimobranchial body of the fourth pouch
What is a thyroglossal cyst?
Cystic remnant of the thyroglossal duct
Where are thyroglossal cysts found?
At any point along the migratory pathway of the thyroid near midline of the neck
Approx 50% near to or just inferior to the hyoid bone
What is a thyroglossal fistula?
When a thyroglossal cyst opens to the outside, connected by a fistulous canal
May arise after rupture of a cyst or at birth
Where is ectopic thyroid tissue normally found?
Anywhere along the pathway of descent of the thyroid
Commonly in base of tongue, just behind foramen cecum and subject to the same diseases as the thyroid gland itself
What is first arch syndrome?
Spectrum of defects in the development of eyes, ears, mandible and palate
Result of failure of colonisation of the first arch with neural crest cells
What is presentation of first arch syndrome called?
Treacher-Collins syndrome
What is the inheritance of Treacher-Collins syndrome?
Autosomal dominant
Signs of first arch syndrome?
Hypoplasia of mandible and facial bones, low-set ears
What is DiGeorge syndrome?
Congenital thymic aplasia and absence of parathyroid
Signs and symptoms of DiGeorge syndrome?
Cardiac abnormalities Abnormal face Thymic aplasia Cleft palate Hypocalcaemia/hypoparathyroidism 22 - deletion of chromosome 22
What is CHARGE syndrome?
When there is a heterozygous mutation of CHD7 protein
It is essential for production of multipotent neural crest cells
Signs and symptoms of CHARGE syndrome?
Coloboma (hole in iris) Heart defects Atresia (choanal) - blockage of posterior nasal cavity Retardation of growth and development Genital hypoplasia Ear defects
What type of control are the two lobes of the pituitary under?
Posterior - neuroendocrine
Anterior - endocrine
