Development 2

Question 1

Whar are the 2 parts of the pituitary developed from

Answer 1

• The pituitary has ectoderm AND neurectoderm origins

• Rathke’s pouch is the Ectoderm component
- Anterior pituitary

• Infundibulum is Neurectoderm component (derived from neuroectoderm)
- Posterior pituitary and stalk

Little bit of ectoderm becomes specialised - grows up as rates pouch. Infundibulum grows down - a bit of neuroectoderm. They join together
Then bones get ossified. Removes link between rathkes pouch and oropharynx.

Question 2

Descirb the infunibulum

Answer 2

• Neural tube component
• Downward out-growth of the forebrain
• grows towards the roof of the pharynx

Question 3

What is rathkes pouch

Answer 3

• Out-pocketing of ectoderm of the stomatodeum
• An evagination of the roof of the (oro-) pharynx
• Grows dorsally towards the developing forebrain

Question 4

What is the lingual frenulum

Answer 4

Cord that tethered the base of tongue to floor of oral cavity

Question 5

What is the sulcus terminalis

Answer 5

Boundary between anterior 2/3 and posterior 1/3 of the tongue
V shape
Point of the V is the foramen cecum

Question 6

When does the tongue begin to develop

Answer 6

• Primordia of the tongue appear at about the same time as the palate begins to form
• Receives a component from
each of the Pharyngeal arches

Question 7

What are the lingual swellings

Answer 7

Lingual swellings grow up from loot of pharynx. Each is a mass of tissue.

• 2 lateral lingual swellings
From Ph Arch 1

• 3 median lingual swellings:

• Ph Arch 1: Tuberculum impar
• Ph Arch 2 & 3 (+4): Cupola
• Ph Arch 4: Epiglottal swelling

Question 8

How do the lingual swellings develop

Answer 8

• Lateral lingual swellings over-grow the tuberculum impar
• The 3rd arch component of the
cupola over-grows the 2nd arch component
• Extensive degeneration occurs,
freeing tongue from the floor of the oral cavity
• lingual frenulum - mainatains connection

Question 9

Describe teh sensory innervation of the tongue

Answer 9

• Mucosa of anterior 2/3s derived from Ph As 1 & 3 therefore General sensory innervation CN V & IX
• Posterior 1/3 derived from Ph A 3 (& 4) therefore General & special sensory CN IX & X

• taste buds develop in papillae - Special sensory innervation CN VII

Question 10

Describe the development of chorda tympani

Answer 10

• branch of CN VII, nerve of second arch • BUT
• passes into first arch
• THEREFORE
• passes through middle ear (which is a structure which develops between ph arch 1-2)

Question 11

Describe teh motor innervation of the tongue

Answer 11

• Both intrinsic & extrinsic muscles of the tongue develop from myogenic precursors that MIGRATE into the developing tongue
• CN XII
Myogenic precursors come from somites.. each somite receives a branch from the cn xii. Move caudal to cranial, taking cn xii with them. Allows function of the tongue movement - changing shape and position

Question 12

Where foes the thyroid gland initially appear

Answer 12

• Primordium of the thyroid gland appears in
the floor of the pharynx between the tuberculum impar and the cupola
• Final position is anterior neck
• HOW????

Question 13

Describe the descent of the thyroid

Answer 13

• Point of origin for the descent of the thyroid is later marked by foramen cecum
• Bifurcates and descends as a bi-lobed diverticulum connected by the isthmus
• During its descent the thyroid gland remains connected to the tongue by the thyroglossal duct
• Pyramidal lobe (remnant of duct)
• Approx 50% of population

Question 14

What a re some thyroid abnormalities

Answer 14

• Thyroglossal cysts & fistulae
Fluid filled cyst -
Sometimes duct can have abnormal opening onto surface - fistulae but these are less common
• Ectopic thyroid tissue - At some point along the descent - some gets left behind

Question 15

How can you tell the difference between a thyroglossal cyst and a bronchial cyst

Answer 15

Thyroiglossal cyst will like along path of decent of thyroid. A bronchial cyst is a remnant of one of the pharyngeal cleft - the anatomical landmark to determine is the SCM

Question 16

What is fist arch syndrome

Answer 16

• First arch syndrome
• spectrum of defects in development of the eyes, ears, mandible &
palate
• Thought to result from failure of colonisation of the 1st arch with
neural crest cells
• Example – Treacher Collins Syndrome

Question 17

What is treacher-Collins syndrome

Answer 17

• Characterised by hypoplasia of mandible & facial bones
• Inherited, autosomal dominant condition
• Haploinsufficiency of Treacle, a serine/alanine rich nucleolar phosphoprotein. It is involved in
ribosomal DNA gene transcription as well as in processing of the pre-ribosomal RNA. Deficiency of
treacle leads to insufficient ribosome biogenesis, and impacts on NC migration

Question 18

Describ eteh syndromes resulting from the abnormal deveopment of first and second pharyngeal arches

Answer 18

Ss

Question 19

What is di-George syndrome

Answer 19

• Congenital thymic aplasia & absence of parathyroid glands
• Syndrome including a variety of additional defects
• “C!TCH22”
• Deletion on Chromosome 22
• Disruption of development of 3rd and 4th pharyngeal pouches
• Abnormal development of neural crest

Question 20

What is charge syndrome

Answer 20

• CHD7 (chromodomain helicase DNA- binding domain, ATP-dependant
chromatin remodeller) 
• CHARGE syndrome
  - CHD7 heterozygous mutation
• CHD7 expression essential for the
production of multipotent NC