S11) Development of Midline Structures Flashcards
Describe the structure and location of the pituitary gland
- Location: closely related to the hypothalamus
- Structure:
I. Anterior lobe – endocrine secretion
II. Posterior lobe – neuroendocrine secretion
Describe the embryological origins of the pituitary gland
- Ectoderm → Rathke’s pouch → Anterior pituitary
- Neurectoderm → Infundibulum → Posterior pituitary
What is Rathke’s pouch?
- Rathke’s pouch is an out-pocketing of ectoderm of the stomatodeum
- It is formed from an evagination of the roof of the (oro-) pharynx and grows dorsally towards the developing forebrain
What is the infundibulum?
The infundibulum is a downward out-growth of the forebrain which grows towards the roof of the pharynx
What is the sulcus terminalis?
The sulcus terminalis is a V-shaped shallow groove that separates the dorsum of the tongue into a superior oral surface, and a posterior pharyngeal surface
What is the foramen cecum?
- The foramen cecum is a shallow depression in the posterior midline of the tongue which marks beginning of the terminal sulcus
- It is also the point of attachment of the thyroglossal duct and is formed during the descent of the thyroid diverticulum in embryonic development
Describe the embryonic origins of the tongue
The tongue receives a component from each of the pharyngeal arches
When does the tongue begin to form?
Primordia of the tongue appear at about the same time as the palate begins to form
Describe the second stage in the development of the tongue (lingual swellings)
- 2 lateral lingual swellings → Ph Arch 1
- 3 median lingual swellings:
I. Ph Arch 1 → tuberculum impar
II. Ph Arch 2,3&4 → cupola
III. Ph Arch 4 → epiglottal swelling
Describe the final stage in the development of the tongue (overgrowth & lingual frenulum)
- Lateral lingual swellings over-grow tuberculum impar
- 3rd arch component of the cupola over-grows the 2nd arch component
- Extensive degeneration occurs, freeing tongue from oral cavity floor (lingual frenulum)
What is the lingual frenulum?
The lingual frenulum is a small fold of mucous membrane extending from the floor of the mouth to the midline of the underside of the tongue
Describe the embryonic development & sensory innervation of the anterior and posterior parts of the tongue
- Ph Arch 1&3: mucosa of anterior 2/3s
⇒ General & special sensory innervation CN V & IX
- Ph Arch 3&4: mucosa of posterior 1/3
⇒ General & special sensory innervation CN IX & X
Describe the embryonic development & sensory innervation of the taste buds
Taste buds develop in papillae
⇒ Special sensory innervation CN VII
Describe the embryonic development & motor innervation of muscles of the tongue
Both intrinsic & extrinsic muscles of the tongue develop from myogenic precursors that which migrate into the developing tongue
⇒ Motor innervation CN XII
Where does the initial embryonic development of the thyroid gland occur?
Primordium of the thyroid gland appears in the floor of the pharynx between the tuberculum impar and the cupola
Describe the descent of the thyroid gland
- Thyroid gland bifurcates and descends as a bi-lobed diverticulum connected by the isthmus
- Thyroid remains connected to the tongue by the thyroglossal duct
What marks the point of origin for the descent of the thyroid?
Point of origin for the descent of the thyroid is marked by foramen cecum
The thyroid gland is a midline diverticulum in floor of pharynx.
Where does the thyroid gland descend to?
Thyroid gland migrates anterior to pharyngeal gut, hyoid bone & laryngeal cartilages
Identify some thyroid abnormalities that have embryonic origins
- Thyroglossal cysts & fistulae
- Ectopic thyroid tissue
What is Treacher-Collins Syndrome?
- Treacher Collins Syndrome is an inherited, autosomal dominant condition characterised by hypoplasia of mandible & facial bones
- It is thought to result from the failure of colonisation of Ph Arch 1 with neural crest cells
What is Di-George Syndrome?
- Di-George Syndrome is a condition characterised by congenital thymic aplasia & absence of parathyroid glands due to a deletion on chromosome 22
- It is caused by the disrupted development of the 3rd and 4th pharyngeal pouches and the abnormal development of neural crest
What is CHARGE Syndrome?
- CHARGE Syndrome is a condition caused by a heterozygous mutation of the CHD7 protein which is essential for the production of multipotent neural crest
- It presents with coloboma, heart defects, choanal atresia, growth & developmental retardation, genital hypoplasia and ear defects
