Week 10.0 - Development of midline structures

Question 1

What is the sella turcica?

Answer 1

-The bony pocket where the pituitary sits

Question 2

What is the infundibulum with regards to pituitary development?

Answer 2

-A downward outgrowth of the forebrain which gives rise to the posterior pituitary and the neural stalk

Question 3

What is rathke’s pouch?

Answer 3

-An outpocketing of ectoderm of the stomatodeum which grows dorsally towards the developing forebrain and becomes the anterior pituitary after ossification of the skull

Question 4

Describe how the pharayngeal arches contribute to the development of the tongue

Answer 4

1) Mesenchyme proliferations in each of the pharyngeal arches appear in the floow of the oral cavity at the same time as the palate develops
- Ph A1-> two lateral swellings and medial tuberculum impat
- Ph A2,3 and 4 -> cupola
- Ph A4 (6) -> epiglottal swelling
2) Lateral swellings overgrow TI and the 3rd arch copula overgrows the 2nd
3) Extensive degeneration by apoptosis occurs freeing the tongue from the oral cavity (lingual frenulum)

Question 5

What tethers the tongue to the floor?

Answer 5

-Lingual frenulum

Question 6

What/where is sulcus terminalis?

Answer 6

-grooves on the posterior 1/3 of the tongue

Question 7

What/where is foramen cecum?

Answer 7

-Demarkation on the tongue where sulcus terminalis meet. denotes the point of descent of the thyroid

Question 8

Describe the sensory innervation to the tongue

Answer 8

• Ant 2/3 -> special sensory = chorda tympani (VII), general sensory = V3 (lingual branch)
• Post 1/3 gen and special = CNIX (small section by CNX)

Question 9

Through what part of the ear does chorda tympani pass? What is the clinical significance of this?

Answer 9

• Middle ear

- Can affect taste in otitis media and other middle ear infections

Question 10

From where do the muscles of the tongue develop?

Answer 10

-Myogenic precurors of occipital somites which migrate into the developing tongue

Question 11

Describe the motor innervation of the tongue

Answer 11

-Hypoglossal

Question 12

Where does the primordia of the thyroid gland appear?

Answer 12

-In the floor of the pharynx between tuberculum impar and cupola

Question 13

Describe the descent of the thyroid gland

Answer 13

• Begins at what is later the foramen cecum and bifurcates and descends as a bi-lobed diverticulum connected by an isthmus
• Remains connected to tongue during descent by thyroglossal duct
• Looses patency after developed

Question 14

What is a pyramidal lobe of the thyroid?

Answer 14

-Normal variant which remains in 50% of the population and is associated with a remnant of the thyroglossal duct

Question 15

What is a thyroglossal cyst?

Answer 15

-Cyst which forms in a persistent thyroglossal duct

Question 16

Why can the development of the thyroid gland make it possible to get ectopic thyroid tissue?

Answer 16

• Remnants of the thyroglossal duct

- Failed descent of all or part of the thyroid

Question 17

Name some differentials of swellings in the neck (not tumour)

Answer 17

• Branchial cyst
• Thyroid goitre
• Cerivcal lymphadenopathy
• Thyroglossal cyst

Question 18

What is the cause of a cleft lip and palate?

Answer 18

-Failed fusion of the FNP with the palatal shelves of the maxillary prominence of the 1st Ph A

Question 19

What is first arch syndrome?

Answer 19

-A spectrum of defects in development involving the eyes, ears mandible and palate as a result of failed colonisation of the 1st Ph A with neural crest cells

Question 20

What is treacher-collins syndrome?

Answer 20

• Form of first arch syndrome which is an autosomal dominant condition
• Characterised by hypoplasia of the mandible and facial bones

Question 21

What is di-george syndrome?

Answer 21

-Disorder of the pharyngeal pouches resulting in congenital thymic aplasia and absence of the parathyroid gland due to abnormal development of neural crest cells
CATCH 22 (deletion of Chromosome 22)
-Cardiac abnormality
-Abnormal facies
-Thymic aplasia
-Cleft palate
-Hypoparathyroidism