Embryology II Flashcards
What are the two parts of the pituitary?
Posterior lobe - neuroendocrine
Anterior lobe - Endocrine
How does the embryonic development of pituitary explain the two parts?
It has both ectoderm and neuroectoderm origins
Ectoderm = Ratke’s pouch = anterior pituitary
Neuroectoderm = infundibulum = posterior pituitary
What is the infundibulum?
A derivative of the neural tube
It is a downwards outgrowth of the forebrain.
It grows towards the pharynx.
What is Rathke’s pouch?
Out-pocketing of ectoderm of the stomatodeum
An evagination of the roof of the oro-pharynx.
Grows dorsal towards the developing forebrain.
How do these growths become pituitary?
Bones ossify
What is the sulcus terminalis?
A V shaped line in the tongue that separates posterior and anterior tongue.
Foramen caecum is the point of the v.
How does the tongue develop?
Primordial of the tongue appear at about the same time as the palate begins to form.
Receives a component from each of the pharyngeal arches.
Lateral lingual swelling over-grow the tuberculum impar.
The 3rd arch component of the cupola over-grows the 2rd arch component.
Extensive degeneration occurs, freeing the tongue from the floor of the oral cavity. -So it is just attached by the lingual frenulum.
How much of the lingual frenulum remains dictates how mobile the tongue it.
What parts of the tongue develop from each pharyngeal arch?
1st - 2 lateral lingual swellings.
2nd - 3 median lingual swellings.
2nd and 3rd - cupola
4th - Epiglottal swelling
How does the development of the tongue explain the sensory innervation?
Mucosa of anterior 2/3s derived from Ph A 1&3 -General sensory innervation CN V & IX
Posterior 1/3 derived from Ph A 3 (&4) -General & special sensory CN IX & X
Taste buds develop in papillae - Special sensory innervation CN VII
How can you explain the fact that taste buds are innervation by CN VII?
Chorda tympani - branch of the facial nerve (nerve of second arch)
BUT, passes into first arch and therefore through the middle ear.
How can you explain the motor innervation of the tongue?
Both intrinsic and extrinsic muscles of the tongue develop from myogenic precursors that MIGRATE into the developing tongue - CN XII (hypoglossal).
Where does the primordium of the thyroid first appear?
Floor of pharynx between the tuberculum impar and the cupola
Describe the descent of the thyroid
Thyroid begins at the foramen caecum
It bifurcates and descends as a bi-lobed diverticulum connected by the isthmus.
What is the thyroglossal duct?
The thyroglossal duct is what connects the thyroid to the tongue during its descent.
How do cleft lip and palate form?
Palate is formed from palatal shelves which grow medially into oral cavity from the maxillary prominence.
Once mandible has enlarged sufficiently to allow the tongue to “drop” the palatal shelves meet in the midline and fuse.
Cleft lip and palate result from failure of FNP to fuse with Max P and failure of palatal shelves to fuse.
