5. Embryology Of Head And Neck Flashcards
What does the endoderm tube develop into?
Glandular development:
- parathyroid
- thymus
- palatine tonsils
- thyroid
What are the pharyngeal arches?
Comprised of a system of mesenchymal proliferations in the neck region
5 in total (1-6, 5 does not form)
Together will frontonasal prominence constitute the building blocks for the head and neck region
What does each pharyngeal arch have?
An associated artery, nerve (cranial nerve) and cartilage bar
Which cranial nerves are associated with pharyngeal apparatus?
CNV, VII, IX, X
Where do muscles of mastication originate from?
Pharyngeal arch 1 derivatives
Where do muscles of facial expression originate from?
Pharyngeal arch 2 derivatives
What muscles derives from the third pharyngeal arch?
Stylopharyngeus
What muscles derive from the 4th pharyngeal arch?
Cricothyroid
Levator palatini
Constrictors of the pharynx
What muscle derives from the 6th pharyngeal arch?
Intrinsic muscles of the larynx
What do the cartilages of first pharyngeal arch become?
Malleus and incus plus a template for formation of the mandible
What do the cartilages for the second pharyngeal arch become?
Stapes plus upper part of hyoid bone
What do the cartilages of the third pharyngeal arch become?
Remainder of thyroid bone
What do the cartilages of the 4th and 6th pharyngeal arches become?
Cartilages of the larynx
What happens to the 1st and 2nd arch arteries?
Disappear
What does the 3rd arch artery become?
Internal carotid artery
What does the 4th arch artery become?
Arch of aorta (L) and brachiocephalic (R)
What does the 6th arch artery become?
Pulmonary arch
What are pharyngeal pouches?
Endoderm lined pockets in the pharynx
What does the first pharyngeal pouch become?
Tympanic cavity
What does development of the pharyngeal pouches result in?
Formation of palatine tonsils and parathyroid glands and the thymus
Which is the only pharyngeal cleft that remains and what does it become?
1st cleft
Becomes external acoustic meatus
What happens to most of the pharyngeal clefts?
2nd arch grows down to cover them, obliterating them
What happens if the 2nd arch does not develop normally and does not cover all clefts?
Branchial cyst may form
Branchial fistula may form
What drives development of the face?
Expansion of the cranial neural tube
Appearance of a complex tissue system
Development of the sense organs and the need to separate respiratory tract from GI tract
What forms the facial primordia?
1st pharyngeal arch
Frontonasal prominence
What are the components of the face embryologically?
Stomatodeum - buccopharyngeal membrane
Frontonasal prominence
1st pharyngeal arch - maxillary and mandibular prominences
What does the frontonasal prominence develop into?
Forehead
Bridge of nose
Nose
Philtrum
What does the maxillary prominence develop into?
Cheeks
Lateral upper lip
Lateral upper jaw
What does the mandibular prominence develop into?
Lower lip and jaw
How does the nose develop?
- Nasal placodes appear on frontonasal prominence
- Then sink to become the nasal pits
- Medial and lateral nasal prominences form on either side of the pits
- Maxillary prominences grow medially, pushing the nasal prominences closer together in the midline
- Maxillary prominences fuse with medial nasal prominences
- medial nasal prominences then fuse in midline
How are the nasal and oral cavities separated?
Fusion of medial nasal prominences creates the intermaxillary segment
- labial component: philtrum
- upper jaw: 4 incisors
- palate: primary palate
What is a lateral cleft lip?
Failure of fusion of medial nasal prominence and maxillary prominence
What is a cleft lip and cleft palate?
Combined failure of palatal shelves to meet in midline
What component of the ear develops from the 1st pharyngeal cleft?
External auditory meatus
What do the middle ear cavity and ossicles develop from?
1st pharyngeal pouch and cartilages of 1st and 2nd arches
What do auricles develop from?
Proliferation within the 1st and 2nd pharyngeal arches surrounding the meatus
Where does the tongue lie?
Partly in the oral cavity and partly in the pharynx
What attaches the tongue to the floor of the mouth?
Lingual frenulum
What separates the anterior 2/3 from the posterior 1/3 of the tongue?
Sulcus terminalis
What is the point of the sulcus terminalis called?
Foramen cecum
When do the primordia of the tongue appear?
At same time as palate begins to form
Which pharyngeal arch contributes to the tongue?
All of them
What do the 2 lateral lingual swellings develop from?
Pharyngeal arch 1
What do the 3 median lingual swellings develop from?
Pharyngeal arch 1 - tuberculum impar
Pharyngeal arch 2,3,4 - cupola
Pharyngeal arch 4 - epiglottal swelling
How is the lingual frenulum formed?
Extensive degeneration occurs, freeing tongue from the floor of the oral cavity
Where does the primordium of the thyroid gland appear?
In floor of pharynx between the tuberculum impar and cupola
Where is the point of origin for the descent of the thyroid?
Marked y the foramen cecum
What happens in the descent of the thyroid?
Bifurcated and descendsas a bi-lobed diverticulum connected by the isthmus
How does the thyroid gland remain connected to the tongue?
By the thyroglossal duct
What are some thyroid abnormalities?
Thyroglossal cysts and fistulae
Ectopic thyroid tissue
What structures in the developing face must rise to form the upper lip and jaw?
Maxillary prominence and medial nasal prominences
To what structures in the head and neck do neural crest cells contribute?
Cartilage bars in each of the pharyngeal arches leading to development of the skeleton of the face
What structures develop from the 3rd and 4th pouches?
Parathyroid glands and thymus
