11 - Development Of Midline Structures Flashcards Preview

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Flashcards in 11 - Development Of Midline Structures Deck (20):

Where is the pituitary gland located?

The sella turcica/pituitary fossa of the sphenoid bone


What are the two parts of the pituitary gland?
What are the tissue origins of these parts?

Anterior lobe - ectoderm origin (forming endocrine tissue)
Posterior lobe - neuroectoderm origin (neuro-endocrine tissue)


How is the posterior pituitary gland formed?

Posterior lobe grows down from the forebrain in the midline to form the infundibulum.
Extends down to the roof of oral cavity and keeps its connection with the brain which will form the pituitary stalk


How is the anterior pituitary gland formed?

An outpocketing of ectoderm from the roof of the oral cavity (Rathke's pouch) grows up towards the developing brain. It loses its connection with the roof of the mouth. It comes to lie anterior to the infundibulum and wraps around the pituitary stalk. The cells differentiate in to endocrine cells.


What happens after the anterior pituitary gland has lost its connection with the roof of the oral cavity?

Ossification of the sphenoid bone to separate the oral cavity from the cranial cavity


When does development of the tongue begin?

In the 4th week
It appears at the same time as the development of the secondary palate


What is the sulcus terminalis?

The boundary between the anterior 2/3 and the posterior 1/3 of the tongue. The v created at this point is the foramen caecum


How is the primitive tongue tethered to the floor of the oral cavity?

By the lingual frenulum
(Cord-like structure - highly mobile)


What are the key components of the developing tongue?

2 lateral lingual swellings from PA1
Tuberculum impar from PA1
Cupola from PA2,3,4
Epiglottal swelling from PA4


What happens in the development of the tongue?

The lateral lingual swellings grow over the tuberculum impar and extend anteriorly. The 3rd arch component of the cupola grows over the 2nd arch component. The anterior and posterior parts of the tongue fuse with each other. Extensive degeneration occurs to free the tongue from the floor of the oral cavity.


What is special about the chorda tympani?

It passes in to the first arch to pass through the middle ear cavity to innervate special sense to the anterior 2/3 of the tongue


How does the tongue receive motor innervation?

The intrinsic and extrinsic muscles come from myogenic precursors that migrate from occipital somites. They are innervated by the hypoglossal nerve.


What happens in the development of the thyroid gland?

An epithelial growth called the thyroid diverticulum arises from the foramen cecum. It descends along the anterior midline of the neck and the distal end becomes bi-lobed. It remains attached to the foramen cecum by the thyroglossal duct. It descends anterior to the hyoid bone and the larynx.


What structure is a remnant of the thyroglossal duct?

Pyramidal lobes of the thyroid gland


The thyroid gland is composed of different cell types. What are their embryonic origins?

The follicular cells originate from the thyroid decent from the foramen cecum. The parafollicular cells (C cells) come from the ventral aspect of the fourth pharyngeal pouch (ultimobranchial body)


What are thyroglossal cysts?
Where are they found?

Abnormal portions of the thyroglossal duct
These are always midline structures.


What is meant by a first arch syndrome?

A spectrum of defects in development of the eyes, ears, mandible and palate. It is due to neural crest cells failing to colonise the first PA


What is the role of CHD7 expression?

It is essential for the production of multipotent neural crest cells


What happens in Treacher-Collins syndrome?

Inherited autosomal condition characterised by hypoplasia of the mandible and facial bones, low set ears


What is meant by a CHARGE syndrome?

Coloboma (hole in the iris)
Heart defects
Atresia (choanal)
Retardation of growth and development
Genital hypoplasia
Ear defects