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Head and Neck > Embryology > Flashcards

Embryology Flashcards

1
Q

What are pharyngeal arches

A

Pharyngeal arches are a sequence of ridges that form in the lateral walls of embryonic pharynx at the cranial end

Arches appear after 4wks and form the structures of the head and neck

Arches are formed of a mesenchyme core covered externally by ectoderm and internally by endoderm

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2
Q

What are found between pharyngeal arches externally

A

Pharyngeal clefts are found between pharyngeal arches

Clefts disappear as the 2nd arch grows down to over the others

1st cleft remains - forms external auditory meatus

Brachial clefts/fistulae can occur if there are remnants of the clefts - are found medial to SCM

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3
Q

What are found between pharyngeal arches internally

A

Pharyngeal pouches are found between pharyngeal arches

Glandular structures arise form these pouches

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4
Q

How are pharyngeal arches named

A

Pharyngeal arches are numbered 1-6 - 5th arch does not form in humans

1st arch is split into maxillary and mandibular prominences

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5
Q

What is associated with each arch

A

Artery

Nerve

Cartilage bar - 1st arch’s cartilage bar (Meckel’s cartilage) gives rise to mandible, malleus and incus bones

Cartilage becomes skeletal element of head and neck

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6
Q

What arteries and nerves are associated with each arch

A

Common, external and internal carotid arteries and branches are assocaited with 1st, 2nd and 3rd arches

Aortic arch and subclavian artery are assocaited with 4th arch

Pulmonary arteries are assocaited with 6th arch

Trigeminal nerve is associated with 1st arch

Facial nerve is associated with 2nd arch

Glossopharyngeal nerve is associated with 3rd arch

Vagus nerve is associated with 4th and 6th arches

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7
Q

What are the structural derivatives of the 1st arch

A

Muscles of mastication

Mylohyoid

Anterior belly of digastric

Tensor tympani

Tensor veli palatine

Maxillae and zygomatic bones

Meckel’s cartilage - mandible, malleus and inucs

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8
Q

What are the structural derivates of the 2nd arch

A

Muscles of facial expression

Stapedius

Stylohyoid

Posterior belly of digastric

Reichert’s cartilage - superior part of hyoid, stapes, styloid process, stylohyoid ligament

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9
Q

What are the structural derivates of the 3rd arch and what do the 3rd and 4th arches form

A

3rd arch: stylopharyngeus (pharynx muscle) and inferior part of hyoid body

3rd and 4th arch: epiglottis

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10
Q

What are the structural derivates of the 4th and 6th arches

A

Constrictor muscles of pharynx and muscles of soft palate (4th)

Levator palatini (4th)

Cricothyroid (4th)

Intrinsic muscles of larynx (6th)

Striated muscle of upper oesophagus

Cartilage of larynx

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11
Q

What structures are formed form the pharyngeal pouches

A

1st: tympanic caivty -> pharyngotympanic tube and middle ear cavity
2nd: palatine tonsil
3rd: inferior parathyroid and thymus
4th: superior parathyroid, C cells of thyroid

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12
Q

What does the face develop from

A

Face develops from facial primordia: frontonasal prominence, two maxillary prominences and two mandibular prominences

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13
Q

What do the parts of the facial primordia form

A

Frontonasal prominence: forehead, bridge of nose, upper eyelids, centre of upper lip

Maxillary prominences: middle third of face, upper jaw, most of the lip and sides of the nose

Mandibular prominences: lower third of face including the jaw and lip

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14
Q

What is some of the first evidence of facial development

A

The stomodaeum - depression in ectoderm on the ventral aspect of the head (future site of the mouth)

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15
Q

What is the first evidence of nose formation

A

Appearance of nasal placodes on either side of the midline, on ventrolateral aspect of frontonasal prominence

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16
Q

What are placodes

A

Placodes - area of ectoderm that starts to thicken and differentiate itself to form sensory structures

17
Q

How do nasal pits develop

A

Nasal placodes invaginate and form nasal pits

18
Q

What separates the nasal pits from the stomodaeum

A

The oronasal membrane - disappears so the oral and nasal cavities becomes continuous

19
Q

Describe the development of the palate

A

Maxillary prominences grow medially, pushing nasal prominences closer together in the midline

Maxillary prominences fuse with medial nasal prominences

Medial nasal prominences merge in the midline separating the nostrils from the mouth - forms the philtrum

Fusion of medial nasal prominences forms intermaxillary segment

Palatal shelves grow from each maxillary prominence towards the midline

Mandible grows large enough to allow tongue to drop so that palatal shelves can fuse in midline

Palatal shelves fuse together and with the primary palate to form secondary palate - fusion separates nasal cavity from oral cavity

Nasal septum develops as a midline down growth and fuses with palatal shelves to divide nasal cavity in two

20
Q

Where do the parts of the ear develop from

A

External auditory meatus develops from 1st pharyngeal cleft

Middle ear cavity and ossicles develop from 1st pharyngeal pouch and cartilage of 1st and 2nd arches respectively

Auricles develop from proliferation within 1st and 2nd arches surrouding the meatus

External ears develop initially in neck and then as mandible grows, ears ascend

21
Q

Name some congenital abnormalities of the face

A

Lateral cleft lip

Cleft lip

Cleft palate

22
Q

What is a lateral cleft lip

A

Failure of fusion of medial nasal prominece and maxillary prominence

One grows further over to compensate

Only affects primitive plate

23
Q

What is a cleft lip

A

Failure of fusion of medial nasal prominence with maxillary prominence

Have a cleft in the centre

Affects primary palate

24
Q

What is a cleft palate

A

Where there is failure of the palatal shelves to meet and fuse in the midline

Affects both primary and secondary palates

25
Q

What parts of the foetal system are particularly sensitive to alcohol

A

Neural crest migration and development

26
Q

What are two conditions caused by alcohol intake during pregnancy

A

Foetal alcohol syndrome - significant and prologned alcohol exposure

Alcohol related neurodegenerative delay - seen with lower levels of alcohol comsumption than FAS

27
Q

Describe the development of the pituitary gland

A

Posterior pituitary begins as downward growth of the forebrain twoards pharynx

Anterior pituitary is formed from Rathke’s pouch which is an invagination of the ectoderm that grows upwards towards developing forebrain. Ossification of the sphenoid pinches off Rathke’s pouch from the ectoderm

28
Q

Describe the formation of the tongue

A

Tongue begins as two lateral swellings and 3 median lingual swellings within arches 1-4

Lateral lingual swellings over-grow the tuberculum impar while at the same time the 3rd arch component over-grows the 2nd arch component, helping to form the tongue

Extensive degeneration occurs to free the tongue from the oral cavity floor though leaves the lingual frenulum

29
Q

How does the sensory innervation of the tongue relate to the pharyngeal arches that form the tongue

A

Mucosa of anterior 2/3s derived from pharyngeal arches 1 and 3 -> general sensory by CN V and XI

Posterior 1/3 is from 3rd and 4th arches -> general sensory and special sensory by CN IX and X

30
Q

What is the name given to the boundary between the anterior and posterior tongue

A

Sulcus terminalis

31
Q

Describe the development of the thyroid gland

A

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

The gland bifurcates and descends, becoming bi-lobed diverticulum joined in the midline by the isthmus

Thryoid gland origin is foramen cecum

32
Q

What is Di-George syndome

A

Congetial thymic aplasia and absence of thyroid glands

Syndromes include additional defects

Have disruption of 3rd and 4th pharyngeal arches and abnormal development of neural crest cells

33
Q

What is CATCH 22

A

Deletion on chromosome 22 causing Di George syndrome - CATCH 22 is mnemonic

Cardiac - aortic arch abnormalities, conotruncal, tricuspid atresia

Abnormal faces - hypertelorism, ear abnormalities

Thymic hypoplasia - cellular immune deficiency

Cellular immune deficiency, Cleft palate

Hypoparathyroidism with hypocalcaemia

22 chromosomal deletion

34
Q

What is CHARGE syndrome

A

CHD7 heteroxygous mutation. CHD7 required for production of multipotent NC

C - coloboma

H - heart defects

A - choanal atresia

R - growth and developmental retardation

G - genital hypoplasia

E - ear defects

Head and Neck (22 decks)

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