H&N Development of midline structures

Question 1

What is the location of the pituitary gland i.e. where does it sit?

Answer 1

Sella Turcica or Pituitary Fossa

of Sphenoid bone

Question 2

What are the 2 components of the pituitary gland?

Answer 2

Anterior Lobe

Posterior Lobe

Question 3

Describe the anterior lobe of the pituitary gland

Answer 3

Adenohypophysis
Rathke’s pouch derivation
Ectoderm origin
Endocrine

Question 4

Describe the posterior lobe of the pituitary gland

Answer 4

Neurohypophysis
Infundibulum derivation
Neuroectoderm origin
Neuroectoderm function

Question 5

How is the posterior lobe of the pituitary formed?

Answer 5

Down-growth of the diencephalon (forebrain) forms in midline - Infundibulum
Infundibulum extends down towards roof of developing oral cavity, retaining its connection with the brain (pituitary stalk)

Question 6

What is Rathke’s pouch?

Answer 6

Out-pushing (ectoderm of stomatadaeum) from roof of oral cavity (Rathke’s pouch) grows up to meet infundibulum
Loses connection with roof of mouth
Lies anterior to infundibulum
Wraps around pituitary stalk

Question 7

What blood vessels link the anterior pituitary lobe to the hypothalamus and posterior lobe?

Answer 7

Hypophyseal portal system

Question 8

What do Rathke’s pouch and the Infundibulum go on to create?

Answer 8

Rathke’s pouch - Anterior pituitary

Infundibulum - Pituitary Stalk & Posterior Pituitary

Question 9

What can remnants of Rathke’s pouch form?

Answer 9

Cysts

Question 10

When does the tongue develop?

Answer 10

Week 4

Question 11

What swellings develop into the tongue?

Answer 11

2 Lateral Lingual swellings (1st Ph arch)
3 Medial Lingual swellings
 - 1st Ph Arch - Tuberculum Impar
 - 2nd & 3rd Ph Arch - Cupola
 - 4th Ph Arch - Epiglottal swelling

Question 12

How is the tongue developed?

Answer 12

Lateral lingual swelling overgrow the Tuberculum Impar
3rd Arch component of Cupola overgrows 2nd arch part
Extensive degeneration occurs
Tongue freed from floor of oral cavity
Except from Lingual Frenulum (mobile connection)

Question 13

What is the (general) sensory innervation to the tongue?

Answer 13

Ant 2/3rds
- Lingual nerve (CN V3 Mandibular) 1st Ph Arch
Post 1/3rd
- Glossopharyngeal nerve (CN IX) 3rd Ph Arch

Question 14

Describe the special sensory innervation to the tongue

Answer 14

Ant 2/3rds
- Chorda Tympani (CN VII)
- Nerve of 2nd Ph arch but passes into 1st Ph arch through middle ear
Post 1/3rd
- Glossopharyngeal nerve (CN IX) 3rd Ph Arch

Question 15

What do the intrinsic & extrinsic muscles of the tongue develop from?

Answer 15

Myogenic precursors
Migrate into developing tongue
- Palatoglossus (CN X)
- All other muscles of tongue (CN XII)

Question 16

How does the thyroid gland develop?

Answer 16

Appears in floor of pharynx
Expansion of mesenchyme between Tuberculum Impar & Cupola
Between 1st & 2nd Ph arches
Marked in the adult by the Foramen Cecum

Question 17

Describe the descent of the thyroid

Answer 17

Final position is the anterior neck
At its point of origin, the thyroid bifurcates & descends as a bi-lobed diverticulum
Connected by the isthmus
During descent, it remains connected to the tongue - Thyroglossal duct

Question 18

What cells are found in the thyroid gland?

Answer 18

Follicular cells
- Secrete thyroxine & Triiodothyronine (T4/T3)
- Formed by thyroid diverticulum (1st & 2nd arch)
Parafollicular cells
- Secrete Calcitonin
- Formed by ultimobranchial body of 4th pouch

Question 19

What are thyroglossal cysts?

Answer 19

Cystic remnant of thyroglossal duct
Any point along migratory path of thyroid
Always near or in the midline
~50% cysts close to, or just inferior to body of hyoid bone

Question 20

What are thyroglossal fistulae?

Answer 20

Thyroglossal cyst connected to the outside by a fistulous canal
Usually arise secondarily after rupture of a cyst
May be present at birth

Question 21

Where might ectopic thyroid tissue be found?

Answer 21

Anywhere along path of descent of thyroid
Commonly base of tongue
Just behind foramen cecum
Subject to same diseases as thyroid gland itself

Question 22

What is first arch syndrome?

Answer 22

Spectrum of defects in development of eyes, ears, mandible & palate
Failure of colonisation of 1st Arch with neural crest cells
Treacher-Collins syndrome - Autosomal Dominant
- Hypoplasia of mandible & facial bones

Question 23

What is Di-George syndrome?

Answer 23

Congenital Thymic asplasia
Absence of parathyroid glands
Deletion on chromosome 22
CATCH 22
C ardiac abnormality (esp tetralogy of Fallot)
A bnormal facies
T hymic asplasia (no development)
C left palate
H ypocalcaemia/ Hypoparathyroidism

Question 24

What is CHARGE syndrome?

Answer 24

CHD7 Heterzygous mutation
CHD7 essential for production of multipotent neural crest cells
C oloboma (keyhole shape hole in iris)
H eart defects
A tresia (bloackage of post nasal cavity)
R etardation of growth & development
G enital hypoplasia
E ar defects