11 - Embryology of midline Flashcards
Where is the pituitary gland found?
In sella turcica, sphenoid bone
What are the two lobes of the pituitary gland and why are there two?
Anterior, endocrine, derived from ectoderm - Rathke’s pouch
Posterior, neuroendocrine, derived from neurectoderm - infundibulum
Describe the growth of infundibulum
Neural tube component
Downward growth of forebrain
Grows towards roof of pharynx
Describe the growth of Rathke’s pouch
Out-pouching of ectoderm of stomatodeum
Envagination of rood of pharynx
Grows dorsally towards forebrain
Describe how the tongue develops
2 lateral lingual swellings - 1st pharyngeal arch
3 median lingual swellings - Pharyngeal arches 1- tuberculum impar, 2-3 - cupola, 4 - epiglottal swelling
Lateral lingual swellings over grow tuberculum impar (1pa)
3rd arch part of cupola overgrows 2nd arch part
Extensive degeneration frees tongue from floor of oral cavity, connected only by lingual frenulum
Explain how the sensory innervation of tongue is linked to its development
Mucosa of anterior 2/3 derived from 1st and 3rd pharyngeal arches - innervated by CN V and IX
Taste buds develop in papillae - VII
Posterior 1/3 derived from 3rd and 4th pharyngeal arches - IX and X
Why does the chorda tympani pass through the middle ear if it is a derivative of the 2nd arch, CN VII?
Travels through the 1st p arch, so it passes through the middle ear
Why is the motor innervation of the tongue different to its sensory innervation?
Intrinsic and extrinsic muscles of the tongue develop from myogenic precursors outside the tongue and migrate in, so innervated by CN XII
How does the thyroid reach its final position?
Descends from the foramen cecum - floor of pharynx
Bifurcates and descends as a bilobed diverticulum connected by the isthmus
Travels anterior to hyoid bone and laryngeal cartilage
Remains connected to the tongue by thyroglossal duct
What abnormalities can form due to problems with the descent of the thyroid?
Thyroglossal cysts and fistulae
Ectopic thyroid tissue
What embryonic structures contribute to the development of the face?
Frontonasal prominence and 1-2nd pharyngeal arches
What structures must fuse to form the upper lip and jaw?
Frontonasal prominence and medial nasal prominence
How is the palate formed?
Palatal shelves from maxillary prominence grow medially into oral cavity
When mandible has enlarged enough that the tongue can drop, the palatal shelves meet in the midline and fuse
How do cleft lip/palates arise?
Failure of frontonasal prominence to fuse with maxillary prominence and failure of palatal shelves to fuse
What is the function of the neural crest in the development of the face?
Form cartilage bars that form the facial structure
