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Head And Neck > Embryology Of Head And Neck > Flashcards

Embryology Of Head And Neck Flashcards

1
Q

What are the Pharyngeal/ Branchial Arches?

When do they begin forming?

A

A series or ridges that form in the Lateral Walls of the Embryonic Pharynx

Week 4 (once folding is completed)

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2
Q

Describe the tissue composition of each Pharyngeal Arch

A
  • Large Mesenchyme core (some neural crest cells migrate in)
  • Covered by Ectoderm on external surface
  • Covered by Endoderm on internal surface
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3
Q

What exists between each arch on their external surfaces?

What happens to these structures/ landmarks as the embryo develops?

A

Pharyngeal Clefts/ Grooves

All clefs eventually disappear, except Cleft 1 which becomes the External Auditory Meatus

(Cleft 1 is between Arch I and II)

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4
Q

What exists between each arch on their internal surfaces?

List 3 important glandular structures that arise from these structures/ landmarks?

A

Pharyngeal Pouches (similar grooves to external surface)

  • Parathyroids
  • Thymus
  • Tonsils
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5
Q

What structures are collectively known as the Pharyngeal Apparatus?

A
  • Pharyngeal Arches
  • Pharyngeal Clefts/ Grooves
  • Pharyngeal Pouches
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6
Q

How many Pharyngeal Arches do humans have? How do they change as we move towards the Caudal end?

A

5 PAs (1,2,3,4 and 6. PA 5 doesn’t form in humans)

Arches get progressively smaller as we move caudally, with PA 1 being the largest

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7
Q

What 3 things are associated with each Pharyngeal Arch?

A
  • Cartilage (As a cartilage bar)
  • A nerve
  • An artery
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8
Q

In a Pharyngeal Arch, how does the Cartilage arise?

What does the cartilage eventually become?

A

The cartilage arises as a Cartilage Bar, and eventually develops into a skeletal element of the Head & Neck

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9
Q

Relate the innervation of the Pharyngeal Arches to that of their derivatives

A

Derivatives of each PA will be innervated by the same cranial nerve that innervated the PA

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10
Q

Identify the Cranial Nerves innervating each Pharyngeal Arch

A
  • PA 1: Trigeminal (V)
  • PA 2: Facial (VII)
  • PA 3: Glossopharyngeal(IX)
  • PA 4: Vagus (X) (Superior Laryngeal Branch)
  • PA 6: Vagus (X) ( Reccurrent Laryngeal Branch)
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11
Q

Identify the Arteries supplying each Pharyngeal Arch

A
  • PA 1,2 and 3: Common, External and Internal carotid arteries and branches (arteries of PA 1 and 2 disappear, leaving PA 3 with Internal Carotid)
  • PA 4: Aortic arch (left) and Subclavian artery (right)
  • PA 6: Pulmonary arteries/ arch
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13
Q

What are the Muscular derivatives of PA 1?

PA 1 derivatives therefore Trigeminal innervation

A
  • The muscles of mastication
  • Mylohyoid
  • Anterior belly of Digastric

(Also, Tensor tympani and Tensor veli palatine)

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14
Q

What are the Muscular derivatives of PA 2?

PA 2 derivatives therefore Facial innervation

A
  • Muscles of facial expression
  • Stapedius
  • Stylohoid
  • Posterior belly of Digastric
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15
Q

What is the Muscular derivative of PA 3?

PA 3 derivative therefore Glossopharyngeal innervation

A

Stylopharyngeus

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16
Q

What are the Muscular derivatives of PA 4,6?

PA 4,6 derivatives therefore Vagus innervation

A

PA 4;

  • Pharynx constrictor muscles
  • Soft palate muscles (Levator veli palatine)

PA 6;
- Intrinsic muscles of larynx

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17
Q

What is the name for the Cartilage bar of PA 1?

What are its derivatives?

A

Meckel’s cartilage

  • Lays out template for Mandible (Via Endochondral Ossif)
  • Malleus and Incus bones
  • Maxillae and Zygomatic bones
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18
Q

What is the name for the Cartilage bar of PA 2?

What are its derivatives?

A

Reichert’s Cartilage

  • Superior hyoid
  • Stapes
  • Styloid process
  • Stylohyoid ligament
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19
Q

What are the derivatives of PA 3 and 4?

What are the derivatives of PA 4 and 6?

A

3: Inferior part of hyoid bone
3 and 4: Epiglottis

4 and 6: Cartilages of Larynx (Thyroid, Cricoid, Arytenoids)

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20
Q

List the derivatives of the Pharyngeal Pouches

A
  • PA 1: Pharyngoympanic/ Eustachian tube + Middle ear cavity
  • PA 2: Palatine tonsil
  • PA 3: Inferior Parathyroid + Thymus
  • PA 4: Superior parathyroid + C cells of thyroid
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21
Q

Which Pharyngal Pouch has no derivative?

A

PP 6

22
Q

What does the facial skeleton arise from?

A

The Facial Primordia

Frontonasal prominence and PA 1

23
Q

What 2 things can we get if one of the Pharyngeal Clefts don’t disappear?

A
  1. A brachial cyst (Fluid filled remnant of the cleft)

2. A branchial fistula

24
Q

What are the 5 building blocks that the face develops from?

A
  • Frontonasal prominence/ process (FNP)
  • 2 Maxillary prominences (Part of PA 1)
  • 2 Mandibular prominences (Part of PA 1)
25
Q

What is the Stomadaeum?

What is it the first sign of?

A
  • A depression in the ectoderm on the ventral spect of the head
  • The site of the future mouth

First sign of face development

26
Q

The 5 prominences/ processes fold around the Stomadaeum to create the face.

What do they form?

A

Frontonasal Prominence (FNP);

  • Forehead
  • Bridge of nose
  • Philtrum and centre of upper lip
  • Upper eyelids

Maxillary processes;

  • Upper lip
  • Upper jaw
  • Cheeks

Mandibular processes;

  • Lower jaw
  • Lower lip
27
Q

Eventually the Mandibular and Maxillary prominences fuse together to complete the face

What 2 abnormalities can result from failure of this fusion

A
  • Facial clefts

- Cleft lip

28
Q

What is a Placode?

A

An area of ectoderm that starts to thicken and differentiate itself from its surrounding tissue to give rise to sensory structures

(Ear develops from an Otic Placode)

30
Q

What happens to the Nasal Placodes as development progresses?

A
  • Invaginate and form deep Nasal Pits, with the entrance of each pit being a future nostril
  • Medial and Lateral nasal prominences form either side of the Nasal Pits
31
Q

The deepening nasal pits lie dorsal to the Stomadaeum.

What structure separates them and what happens to it?

A

The Oronasal Membrane (thin sheet of cells)

This disappears and the Oral and Nasal cavities become one continuous space

32
Q

Which structure needs to develop to separate the Nasal and Oral cavities once the Oronasal Membrane has disappeared?

Which structures are involved in the development of this new structure?

A

The Palate, whose development involves the Maxillary and Medial Nasal Prominences

33
Q

Describe the formation of the Palate from the Maxillary and Medial Nasal Prominences

A
  • MPs grow medially, pushing the MNPs together
  • MNPs fuse together in the midline, forming the Philtrum and the Primary Palate/ Premaxillary portion of palate (a small component of the palate)
  • Palatal Shelves from MPs fuse with each other and with the Primary Palate-> forming the Secondary Palate
34
Q

Clefts of the Nose/ Lip/ Palate can occur due to failed fusion between structures of the developing face

What does a Cleft Lip arise from?
What does a Cleft Lip and Palate arise from?

A

Cleft Lip: Failed fusion of MNP and MP

Cleft Lip and Palate: Failed fusion of MNP and MP, alongside failure of Palatal Shelves to meet

35
Q

Describe the aetiology of why clefts occur

A

Genetic and environmental factors are thought to be involved

Majority tend to only involve upper lip and/or palate

36
Q

What are 2 methods of diagnosis of a cleft lip/ palate?

What are 3 consequences of a cleft lip/ palate?

A

Diagnosis:

  • Ultrasound scans antenatally
  • After delivery

Consequences:

  • Aesthetic implications
  • Feeding difficulties
  • Speech development difficulties
37
Q

A cleft lip/ palate affects 1 in 700 babies and is the most common facial birth defect in the UK.

How can a paediatrician check for the presence of a cleft?

A

Feeling upper part of newborn’s mouth (Hard palate) with a gloved finger

38
Q

At what age can cleft lips and palate repairs be corrected by surgery?

A

Cleft lips: 3 months (Mainly for cosmetic reasons)
Palate repairs: 9-12 months

(Specialist feeding techniques can be used up until this point)

39
Q

Where do external ears develop initially?

A

In the neck

As mandible grows, they ascend to side of head to lie in line with the eyes

40
Q

How does the mandible facilitate formation of the Secondary Palate?

A

Grows to allow tongue to ‘drop’ allowing Palatal Shelves to meet in midline

41
Q

In Fetal Alcohol Syndrome, why can repeated, excessive alcohol intake during pregnancy lead to facial deformities?

(Incidence of FAS and Alcohol Related Neurodevelopmental Disorder is 1 in 100)

A
  • Facial skeleton derived from Neural Crest Cells in Pharyngeal Arches
  • Neural crest migration and brain development are extremely sensitive to alcohol (alcohol very good at killing neural crest cells)
42
Q

The tongue lies partly in the Oral Cavity and partly in the Pharynx, and is composed of Intrinsic and Extrinsic muscles

What structure allows its high mobility?

A

Lingual Frenulum (a short one leads to reduced mobility of tongue)

43
Q

The tongue is split into an Anterior 2/3rds and Posterior 1/3rd.

What marks the boundary?
What is the Foramen Cecum?

A

Boundary: A V-shaped Sulcus Terminalis

FC- Posterior tip of Sulcus Terminalis

44
Q

The Primordia of the tongue appear around the same time as when the palate begins to form

Describe its derivation from the Pharyngeal Arches

A

Receives a component from Pharyngeal Arches 1,2,3 and 4

45
Q

The developing tongue is made up of 2 Lateral Lingual swellings and 3 Median Lingual Swellings

Relate these to the Pharyngeal Arches

A
  • PA 1: Makes up the LLSs and the Tuberculum Impar (Below and central to the LLSs)
  • PA 2,3 and 4: Each make up a MLS and the Cupola (part of each PA)
  • PA 4: Makes up the Epiglottal Swelling (An MLS)
46
Q

Describe how the Lateral and Medial Lingual swellings develop after formation

A
  • LLSs overgrow the Tuberculum Impar
  • PA 3 part of Cupola overgrows the PA 2 part
  • Extensive degeneration occurs freeing tongue from floor of oral cavity (Originally tongue is just a series of lumps on the oral cavity floor)
47
Q

Where does the Primordium of the Thyroid Gland start?

A

In floor of pharynx between Cupola and Tuberculum Impar

48
Q

Describe the Descent of the Thyroid Gland

A
  • Foramen Cecum marks the point of origin, from which the thyroid gland descends (Enters FC and descends through Thyroglossal Duct)
  • Bifurcates and descends as a bi-lobed diverticulum connected by a central Isthmus
  • During descent, Thyroid Gland remains connected to tongue by Thyroglossal Duct
49
Q

List 3 thyroid abnormalities

A
  • Ectopic thyroid tissue
  • Thyroglossal Cyst
  • Thyroglossal Fistula
50
Q

What is the first sign of nose formation?

A

Appearance of 2 Nasal Placodes (ectodermal thickenings) on the Ventrolateral aspect of the Frontonasal prominence

51
Q

Each PA is associated with an Aortic Arch blood vessel (Vessel runs through the mesenchyme core)

As embryo develops, the organisation of the blood vessels is lost.

Describe the result of this on the Recurrent Laryngeal Nerve’s relationship to the arterial system

A

RL branch of Vagus nerve;

  • Loops under Aortic Arch on left side
  • Loops under Subclavian Artery on right side

Head And Neck (20 decks)

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