Flashcards in H&N 9.3 Development of the nose and face Deck (50):
When does the neural tube form in embryonic development?
What structures lead to the formation of the head and neck?
The pharyngeal arches/ branchial arches
What drives development of the face?
-Expansion of the neural tube
-development of the special sense organs
-the appearance of tissues involved in the cranial gut tube and the developing heart outflow.
What are neural crest cells?
a specialised population of cells that originate within the neurectoderm.
("a 4th germ lineage")
Where about do the neural crest cells come from?
The lateral border of the neurectoderm
They then enter the mesoderm and migrate (to contribute with various head and neck structures)
What are the major features of the face?
What is the philtrum?
the groove in the upper lip that extends up to the nose.
What are the palpebral fissues?
the openings in the eye lids
What are the major bones and muscles of the face, and their origins?
-Facial skeleton- from the neural crest of the 1st pharyngeal arch
-muscles of mastication- from the mesoderm of the 1st pharyngeal arch
-muscles of facial expression- from the mesoderm of the second pharyngeal arch
What are the primary facial primordia?
-1st pharyngeal arch (maxillary and mandibular prominence)
What is the stomatodeum?
A depression in the developing face that will go on to give the mouth.
It contains the buccopharyngeal membrane at it's center.
Where is the fronto-nasal prominence found?
Around the ventro-lateral aspects of the brain.
What external features does the FNP give rise to?
-bridge of nose
What external features does the maxillary prominence give rise to?
-lateral upper lip
-lateral upper jaw
What external features does the mandibular prominence give rise to?
-the lower lip and jaw.
What are the nasal placodes?
How do they develop?
Depressions which apprear fairly laterally on the FNP.
They sink to form nasal pits, which will eventually become nostrils.
Either side of the nasal pits you get medial and lateral prominences.
How do the medial nasal prominences develop?
They get pushed more medially by the development of the maxillary prominence.
They eventually fuse at the midline, and fuse with the maxillary prominence.
What is formed when the medial nasal prominences and the maxillary prominence fuse?
The intermaxillary segment.
What does the intermaxillary segment go on to form in the mature face?
-the labial component of the philtrum (middle upper lip)
-the primary palate
-the medial 4 upper incisors.
What is the secondary plate formed of in the face?
The palatal shelves of the maxillary prominences and the pallatine bones.
How are the nasal pits and the oral membrane initially separated?
What happens to this?
Via the oronasal membrane
This quickly ruptures, in the mature face there is connection between the 2 cavities.
Initially, how do the pallatal shelves of the maxillary prominence develop?
They grow vertically downwards, into the oral cavity, either side of the developing tongue
What must happen in order for the pallatal shelves to be able to fuse and form the secondary palate?
The mandible must grow large enough, allowing the tongue to 'drop' further down, and out of the way.
The pallatal shelves of the maxillary prominence fuse together, what else fuses with them?
The nasal septum, which grows down from above.
The lip and palate have dual origin, what are the 2 components?
The maxillary prominence
the intermaxillary segment
What common condition can result from a failure of all the tissues of the mouth developping properly?
A cleft lip.
What is meant by a lateral cleft lip?
There has been failure of the fusion of the medial nasal prominence and the maxillary prominence of one side.
only the lip is involved, not the pallate.
What is meant by a cleft lip and cleft plate?
There has been failure of both the fusion of the medial nasal prominence's and the maxillary prominence,
The maxillary prominences have failed to meet in the midline.
Why does a cleft lip and palate need correctional surgery more so than just a lateral cleft lip?
The child will have difficulty feeding, and later on would lead to speech issues
The cleft lip would be more manageable. (but will still be corrected for cosmetic reasons)
What is the fate of the lateral nasal prominences?
Form the sides of the nose
How do the eyes begin development?
As out-pocketings of the forebrain in the 4th week.
They make contact with the overlying ectoderm.
What are the optic placodes?
What do they represent
Bulges found on the ventro-lateral aspects of the developping face,
Represent the pushing forebrain.
How do the optic placodes go on to form the eye sockets?
optic vesicles (extensions of forebrain) grow out and make contact with the lens placode.
Then there is invagination and pinching off of the lens placode.
What do the optic placodes go on to form?
The lens of the eye
What do the optic vesicles go on to form in the mature face?
The retina of the eye (therefore the retina is made of forebrain, because that's what the optic vesicle is made of)
Where do the eyes begin development, and how does this change?
Begins on the sides of the head
As other facial prominences grow, they push the eyes toward eachother, so they end up on the front of the face, allowing for binocular vision.
Where is the external auditory meatus formed from in the embryo?
The 1st pharyngeal cleft (the only one that should remain)
Where do the auricles of the ear develop from in the embryo?
From the 1st and 2nd pharyngeal arches (those that are either side of the meatus, which is formed from the pharyngeal cleft between the 2)
Where do the ears initially develop?
How does this change?
Initally they develop in the neck.
As the mandible grows, the ears ascend until they lie in line with the eye
What developmental process' depends on the mandible?
-The fusion of the maxillary prominences
-the normal positioning of the ears
From what structure does the inner ear develop from?
The otic placodes
Where are the otic placodes originally found in the embryo?
The posterior head
What do the otic placodes go on to form?
The membranous labrynth of the semilunar canals, and the cochlea.
What is ARND?
Alcohol related neurodevelopmental delay
How common is ARND and FAS?
Seen in around 1 in 100 births.
What is FAS?
Fetal alcohol syndrome
What are some signs of FAS in the newborn?
-small eye openings
-low nasal bridge
-small head (microcephaly)
Why is alcohol so dangerous to unborn fetus?
It is a small mollecule therefore eaily crosses the placental membane, and exert it's teratogenic effects.
Which part of the development of the fetus is affected by alcohol?
The migration of the neural creast cells (which facial development is dependant on)
And development of the brain