Session 5: Development of the Head & Neck 1 Flashcards
In which week does the development of the head begin?
4th week
What begins growing in the 4th week of embryonic development.
Pharyngeal arches.
Where do the pharyngeal arches form?
In the lateral walls of the embryonic pharynx.
Explain the properties of the pharyngeal arches.
They have a mesenchyme core and ectoderm on its external surface.
On its internal surface they are lined in endoderm.
How many pharyngeal arches form?
Theoretically 6 but only 5 in humans.
Pharyngeal arches 1-4 and then 6.
First arch is the biggest one.
What are the pharyngeal arches associated with?
Cartilage, nerve and artery.
What kind of cartilage does the 1st pharyngeal arch form?
Meckel’s cartilage
What does Meckel’s cartilage give rise to?
Mandible, malleus, and incus bones.
What kind of cartilage does the 2nd pharyngeal arch form?
Reichert’s cartilage - stapes (ear) and also of the upper part of the hyoid bone
What kind of cartilage do the 3rd and 4th pharyngeal arches form?
3rd - Inferior parth of body of hyoid
3rd and 4th - Epiglottis
What kind of cartilage do the 4th and 6th pharyngeal arch form?
Larynx cartilage:
Thyroid cartilage
Arytenoids cartilage
Cricoid cartilage
What arteries do the 1st and 2nd pharyngeal arch form?
None
They disappear
What arteries does the 3rd pharyngeal arch form?
Common, external and internal carotid arteries with their branches.
What arteries does the 4th pharyngeal arch form?
Aortic arch and the brachiocephalic trunk
What arteries does the 6th pharyngeal arch form?
Pulmonary arteries
What nerve does the 1st pharyngeal arch form?
Trigeminal nerve (CN V)
What nerve does the 2nd pharyngeal arch form?
Facial nerve (CN VII)
What nerve does the 3rd pharyngeal arch form?
Glossopharyngeal nerve (CN IX)
What nerve do the 4th and 6th pharyngeal arches form?
Vagus nerve (X)
What muscles does the 1st pharyngeal arch form?
Muscles of mastication
What muscles does the 2nd pharyngeal arch form?
Muscles of facial expression
Stapedius
What muscles does the 3rd pharyngeal arch form?
Stylopharyngeus
What muscles do the 4th and 6th pharyngeal arches form?
Inner muscles of the larynx
What can be found between each arch on their external surface?
Pharyngeal clefts
What can be found between each arch on their internal surface?
Pharyngeal pouches
What do the pharyngeal clefts give rise to?
They will all disappear and the only one to remain will be the first pharyngeal cleft.
The 1st pharyngeal cleft will form the external auditory meatus.
What happens if the pharyngeal clefts don’t disappear?
Remnant pharyngeal clefts can become branchial (pharyngeal) cysts anterior to SCM or branchial (pharyngeal) fistulae.
What do the pharyngeal pouches give rise to?
Important glandular structures.
What does the 1st pharyngeal pouch give rise to?
Becomes the tympanic cavity.
Forms the eustachian tube and the middle ear cavity.
What does the 2nd pharyngeal pouch give rise to?
Palatine tonsil
What does the 3rd pharyngeal pouch give rise to?
Inferior parathyroid
Thymus
What does the 1st pharyngeal pouch give rise to?
Superior parathyroid
C cells of the thyroid
What are the arches, clefts and the pouches collectively called?
Pharyngeal apparatus
The development of the face involves five building blocks.
Which?
There is a sixth structure involved. Which?
Frontonasal prominence
Two maxillary prominences
Two mandibular prominences
6th:
Stomatodaeum
What do the two maxillary prominences arise from?
1st pharyngeal arch
What do the mandibular prominences arise from?
1st pharyngeal arch.
What will the frontonasal prominence form?
Forehead
Bridge of nose
Medial and lateral nasal prominences.
What will the medial and lateral nasal prominences form?
Medial: Philtrum, first palate and mid upper jaw
Lateral: Sides of the nose
What will the maxillary prominences form?
Cheeks
Upper jaw
Lateral upper lip
Sides of the nose
What will the mandibular prominences form?
Lower third of the face
Lower jaw
Lower lip
What will the stomatodaeum become?
The future mouth and the buccopharyngeal membrane
Briefly explain the development of the face derived from the five building blocks.
The five prominences will fold around the stomatodaeum to form the face.
Explain the development of the nose.
Two ectodermal thickenings known as nasal placodes will thicken and differentiate. They will form on either side of the midline on the frontonasal prominence.
The nasal placodes will invaginate to form the nasal pits. The entrance to each pit will become the nostrils. Medial and lateral nasal prominences form on either side of the pits.
The nasal pits are separated by the oronasal membrane. This membrane will disappear and the oral and nasal cavities will become one continuous space.
In adults the oral and nasal cavities are not one continous space. How are they separated?
By the palate.
Explain the development of the palate.
The maxillary prominences start to grow medially. This pushes the nasal prominences closer together in the midline.
The medial nasal prominences merge in the midline to separate the nostrils from the mouth to create the intermaxillary segment and forms the philtrum. They also form a small midline component known as the primary palate.
The maxillary prominences gives rise to two palatal shelves. The mandible grows large enough to allow the tongue to drop. The palatal shelf from each maxillary prominence grows towards the midline. These palatal shelves fuse with the primary palate to form the secondary palate. The main part of the palate in adults is the secondary palate.
The secondary palate separates the nasal cavity from the oral cavity.
Give examples of different cleft lips.
Lateral cleft lip
Cleft lip & cleft palate
Explain how lateral cleft lip comes about.
Failure of fusion of the medial nasal prominent and the maxillary prominence.
Can also involve the primary palate.
Explain how cleft lip & cleft palate come about.
Combined failure of fusion of medial nasal prominence and maxillary prominence
with
failure of palatal shelves to meet in the midline.
Causes of cleft lip
Genetic and environmental
How to diagnose cleft lip.
Ultrasounds scan in utero.
Or after delivery
Complications of cleft lip.
Aesthetics
Troubles feeding
Speech development
Treatment of cleft lip.
Cleft lips are treated around 3 months old by surgery.
Cleft palates are treated around 9-12 months old by surgery
Briefly explain the development of the ear.
External auditory meatus develops from the 1st pharyngeal cleft.
The middle ear cavity develop from the 1st pharyngeal pouch.
The ossicles develop from the cartilages of the 1st and 2nd arches (Meckel’s and Reichert’s)
The auricles (external ear) develpo from the proliferation (swelling) within the 1st and 2nd pharyngeal arches to surround the meatus.
Explain the positioning of the ears.
External ears develop initially from the neck and as the mandible grows the ears will be pushed upwards and to the sides of the head to lie in line with the eyes.
(All common chromosomal abnormalities have associated external ear anomalies)
Explain fetal alcohol syndrome.
No known safe level of alcohol consumption during pregnancy.
The facial skeleton derives from neural crest cells and populate the pharyngeal arches. The neural crest migration as well as the development of the brain are known to be extermely sensitive to alcohol.
