Session 6 - development of the head and neck Flashcards
how do the parathyroids, thymus, palatine tonsils and thyroid develop
develop from endoderm lined gut tube in the pharynx
what are the building blocks for the head and neck region
pharyngeal arches and frontonasal porminence
each arch has an associated artery, nerve and cartilage bar
what are the pharyngeal arches
prominent expansion of tissue in the embryonic
head and neck, one of a series of segments in this
region
what is a pharyngeal pouch
the internal surface of a pharyngeal arch, lined by
endoderm of the primitive gut tube
each arch has an associated pouch
which arches are associated with which cranial nerve
1 - CNV 2- CNVII 3- CNIX 4- CNX 6-CNX CNXI and CNXII have relationship with the pharyngeal arch system
how many arches are there
5 in total numbered 1-6
the 5th does not form in humans
what is derived from pharyngeal arch 1
muscles or mastication
meckel’s :malleus and incus plus a template for the formation of the mandible
what is derived from pharyngeal arch 2
muscles of facial expression
reichert’s: stapes plus upper part of hyoid
what is derived from pharyngeal arch 3
stylopharyngeus- The stylopharyngeus is a muscle in the head that stretches between the temporal styloid process and the pharynx. raise the pharynx and larynx during deglutition (swallowing) and laterally draws the pharyngeal walls up
remainder of hyoid bone
what is derived from pharyngeal arch 4
circothyroid
levator palatini
constrictors of the pharynx
cartilages of the larynx
what is derived from pharyngeal arch 6
intrinsic muscles of the larynx
cartilages of the larynx
what does the first pouch become
it is the largest
and becomes the tympanic cavity where the middle ear develops
what happens to the pharyngeal clefts
the first cleft becomes the external acoustic meatus
the second arch grows down to cover others, obliterating all other celfts
what happens if there is abnormal development of the pharyngeal clefts
you get branchial cysts or fistulae
occur on anterior border of SCM
allows tissue fluid to develop in neck
what derives the development of the face
expansion of the cranial neural tube
appearance of a complex tissue system associated with- the cranial gut tube and the outflow of the developing heart
development of the sense organs and the need to separate the respiratory tract from the GI tract
what does the face develop from
• Facial primordia
– 1st pharyngeal arch becomes the maxillary and mandibular prominences
– Frontonasal prominence (FNP)
Surrounds ventro-lateral part of the forebrain
• Primordia of eyes
what does the FNP give rise to
forehead
bridge of nose
nose
philtrum
what does the maxillary prominence give rise to
cheeks
lateral upper lip
lateral upper jaw
what does the mandibular prominence give rise to
lower lip and jaw
how does the nose develop
• Nasal placodes (thickening of ectoderm) 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 the midline
how do the nasal and oral cavities seperate
• Fusion of medial nasal prominences creates the intermaxillary segment
– Labial component: philtrum
– Upper jaw: 4 incisors
– Palate: primary palate
• Main part of definitive palate is secondary palate
– Derived from palatal shelves derived from maxillary prominences
what gives rise to the two palatal shelves
maxillary prominence
the two palatal shevles grow vertically downwards into the oral cavity on each side of the developing tongue
what happens when the two palatal shelves grow
they grow towards each other and fuse in the midline
the nasal septum develops as a midline down-growth and ultimately fuses with the palatal shelves
how do you get a lateral cleft lip
Failure of fusion of medial nasal prominence & maxillary prominence
how do you get a cleft lip and palate
Failure of fusion of medial nasal prominence & maxillary prominence
Combined with failure of palatal shelves to meet in midline
other than aesthetics what problems might occur with a cleft lip and palate
impaired speech development and ability to feed
how does the ear develop
• External auditory meatus develops from the 1st Ph cleft
• Middle ear cavity and ossicles develop from 1st pharyngeal pouch and cartilages of 1st and 2nd arches
respectively
• Auricles develop from proliferation within the 1st and 2nd Ph Arches surrounding the meatus
how do the ears reach their correct position
• External ears develop initially in the neck • As mandible grows the ears ascend to the side of the head to lie in line with the eyes • All common chromosomal abnormalities have associated external ear anomalies
what are the features of fetal alcohol syndrome
small head, low nasal bridge, smooth philtrum, small eye openings, short nose, thin upper lip, flat midface, epicanthal folds
why should you not even drink a small amount of alcohol during pregnacny
- There is no known safe level of alcohol consumption during pregnancy
- Facial skeleton derived from neural crest cells populating the pharyngeal arches
- Neural crest migration as well as development of the brain are extremely sensitive to alcohol
- Incidence of FAS & ARND = 1 / 100 births
