H&N Development of midline structures Flashcards
What is the location of the pituitary gland i.e. where does it sit?
Sella Turcica or Pituitary Fossa
of Sphenoid bone
What are the 2 components of the pituitary gland?
Anterior Lobe
Posterior Lobe
Describe the anterior lobe of the pituitary gland
Adenohypophysis
Rathke’s pouch derivation
Ectoderm origin
Endocrine
Describe the posterior lobe of the pituitary gland
Neurohypophysis
Infundibulum derivation
Neuroectoderm origin
Neuroectoderm function
How is the posterior lobe of the pituitary formed?
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)
What is Rathke’s pouch?
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
What blood vessels link the anterior pituitary lobe to the hypothalamus and posterior lobe?
Hypophyseal portal system
What do Rathke’s pouch and the Infundibulum go on to create?
Rathke’s pouch - Anterior pituitary
Infundibulum - Pituitary Stalk & Posterior Pituitary
What can remnants of Rathke’s pouch form?
Cysts
When does the tongue develop?
Week 4
What swellings develop into the tongue?
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
How is the tongue developed?
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)
What is the (general) sensory innervation to the tongue?
Ant 2/3rds
- Lingual nerve (CN V3 Mandibular) 1st Ph Arch
Post 1/3rd
- Glossopharyngeal nerve (CN IX) 3rd Ph Arch
Describe the special sensory innervation to the tongue
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
What do the intrinsic & extrinsic muscles of the tongue develop from?
Myogenic precursors
Migrate into developing tongue
- Palatoglossus (CN X)
- All other muscles of tongue (CN XII)
How does the thyroid gland develop?
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
Describe the descent of the thyroid
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
What cells are found in the thyroid gland?
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
What are thyroglossal cysts?
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
What are thyroglossal fistulae?
Thyroglossal cyst connected to the outside by a fistulous canal
Usually arise secondarily after rupture of a cyst
May be present at birth
Where might ectopic thyroid tissue be found?
Anywhere along path of descent of thyroid
Commonly base of tongue
Just behind foramen cecum
Subject to same diseases as thyroid gland itself
What is first arch syndrome?
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
What is Di-George syndrome?
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
What is CHARGE syndrome?
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
