S11) Development of Midline Structures Flashcards

1
Q

Describe the structure and location of the pituitary gland

A
  • Location: closely related to the hypothalamus
  • Structure:

I. Anterior lobe – endocrine secretion

II. Posterior lobe – neuroendocrine secretion

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2
Q

Describe the embryological origins of the pituitary gland

A
  • Ectoderm → Rathke’s pouch → Anterior pituitary
  • Neurectoderm → Infundibulum → Posterior pituitary
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3
Q

What is Rathke’s pouch?

A
  • 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
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4
Q

What is the infundibulum?

A

The infundibulum is a downward out-growth of the forebrain which grows towards the roof of the pharynx

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5
Q

What is the sulcus terminalis?

A

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

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6
Q

What is the foramen cecum?

A
  • 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
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7
Q

Describe the embryonic origins of the tongue

A

The tongue receives a component from each of the pharyngeal arches

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8
Q

When does the tongue begin to form?

A

Primordia of the tongue appear at about the same time as the palate begins to form

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9
Q

Describe the second stage in the development of the tongue (lingual swellings)

A
  • 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

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10
Q

Describe the final stage in the development of the tongue (overgrowth & lingual frenulum)

A
  • 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)
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11
Q

What is the lingual frenulum?

A

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

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12
Q

Describe the embryonic development & sensory innervation of the anterior and posterior parts of the tongue

A
  • 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

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13
Q

Describe the embryonic development & sensory innervation of the taste buds

A

Taste buds develop in papillae

⇒ Special sensory innervation CN VII

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14
Q

Describe the embryonic development & motor innervation of muscles of the tongue

A

Both intrinsic & extrinsic muscles of the tongue develop from myogenic precursors that which migrate into the developing tongue

⇒ Motor innervation CN XII

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15
Q

Where does the initial embryonic development of the thyroid gland occur?

A

Primordium of the thyroid gland appears in the floor of the pharynx between the tuberculum impar and the cupola

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16
Q

Describe the descent of the thyroid gland

A
  • Thyroid gland bifurcates and descends as a bi-lobed diverticulum connected by the isthmus
  • Thyroid remains connected to the tongue by the thyroglossal duct
17
Q

What marks the point of origin for the descent of the thyroid?

A

Point of origin for the descent of the thyroid is marked by foramen cecum

18
Q

The thyroid gland is a midline diverticulum in floor of pharynx.

Where does the thyroid gland descend to?

A

Thyroid gland migrates anterior to pharyngeal gut, hyoid bone & laryngeal cartilages

19
Q

Identify some thyroid abnormalities that have embryonic origins

A
  • Thyroglossal cysts & fistulae
  • Ectopic thyroid tissue
20
Q

What is Treacher-Collins Syndrome?

A
  • 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
21
Q

What is Di-George Syndrome?

A
  • 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
22
Q

What is CHARGE Syndrome?

A
  • 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