Lecture 10- Development of the face and nose Flashcards
- External human face develops between
4th and 6th week
- The palate begins to develop between the
6th and 8th week
the palate
- Distinction between the nasal and oral cavities
development of the fsace and nose complete by
12th week
There are two important tissue structures involved in development of the nose and face –
the pharyngeal arches and neural crest cells.
- Neural crest cells
- are a specialised cell lineage which originate from neuroectoderm.
- As the neural tube forms, cells from the lateral border of the neuroectoderm are displaced into mesoderm, and from there they migrate throughout the body to form various structures.
- Of relevance to the head and neck, these cells enter the pharyngeal arches to help contribute to their derivatives.
- the external face is derived from two sources
- frontonasal prominence
- 1st pharyngeal arch
- Mandibular and maxillary prominences
oropharangeal membrane
- Week 3- oropharyngeal membrane appears at the site of the future face- comprised of ectoderm and endoderm- externally and internally, respectively
- During week 4- this membrane begins to break down to become the future oral cavity
- A space lies between the maxillary prominences called the ……………..- precursor to mouth and pituitary gland
stomotodeum
Major facial features:
palpebral fissures, oral fissures, nares (nostril), philtrum
what does the frontal nasal prominence go on to form
- Forehead
- Nose
- Bridge of nose
- Philtrum
what do the maxiallary prominences go on to form
- Cheeks
- Lateral upper lip
- Lateral upper jaw
what does the mandibular prominence go onto form
- Lower lip and jaw
Development of the nose instigated by
the appearance of raised bumps called nasal placodes (thickening of ectoderm) on both sides of the frontal nasal prominence
nasal placodes invaginate to form
nasal pits, with medial and lateral nasal prominences on either side
how are the nasal promincnes pushed closer to the midline to form classic nose
- As the maxillary prominences expand medially, the nasal prominences are pushed closer to the midline
- the maxillary prominences then fuse with the medial nasl proninces
- nmedial nasla prominences then fuse int he mdiline
outline the formation of the definitive palate
- Fusion of medial nasal prominences creates the intermaxillary segment- forms the primary palate (anterior 1/3 of the definitive palate)
- Intermaxillary segment contributes to the:
- Labial component= philtrum
- Upper jaw= 4 incisors
- Palate: primary palate
- Main part of definitive palate is secondary palate
- Maxillary prominences expand medially downwards to give rise to palatal shelves
- At the same time the mandible expands to increase the size of the oral cavity- tongue can drop out of the way of the growing palatal shelves
- These fuse superior to the tongue
- Palatal shelves fuse in the horizontal plane,
- Nasal septum in vertical plane
- Cleft palate=
- palatal shelves from maxillary prominences fusing fails
- Can occur in isolation when the palatal shelves fail to fuse in the midline or in combination with cleft lip
cleft lip and palate summary slide
the external auditroy meatus develops from the
1st pharnagela arch
Positioning of the ear
- External ear develops initially in the neck
- As the 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
The tongue
- Lies partly in the oral cavity and partly in the pharynx
- Highly mobile
- Lingual frenulum- attaches tongue to floor of mouth
- Comprises intrinsic and extrinsic muscles
- Boundary between anterior and posterior determined by the sulcus terminalis
- Foramen cecum = point of V shape sulcus terminalis
- the tongue is derived from pharyngeal arches
1-4 (forms the mucosa of the tongue) and the occipital somite’s (forms the musculature of the tongue)
outline the devolopment of the tongue
Pharyngeal Arches (Mucosa)
In the first stage of development, lingual and medial swellings appear:
- Lateral lingual swellings (x2) – derived from the 1st pharyngeal arch. Contributes to the mucosa of the anterior 2/3 of the tongue.
-
Medial swellings (x3):
- Tuberculum impar – derived from the 1st pharyngeal arch. Contributes to the mucosa of the anterior 2/3 of the tongue.
- Cupola (hypobranchial eminence) – derived from the 2nd, 3rd and 4th pharyngeal arches. Forms the mucosa of the posterior 1/3 of the tongue.
- Epiglottal swelling – derived from the 4th pharyngeal arch. Forms the epiglottis.
During the 4th week, the lateral lingual swellings overgrow the tuberculum impar and merge together – forming the mucosa of the anterior 2/3 of the tongue. Their line of fusion is marked by the median sulcus of the tongue.
Within the cupola, the 3rd pharyngeal arch component overgrows the 2nd arch, and forms the mucosa of the posterior 1/3 of the tongue. The anterior 2/3 and posterior 1/3 fuse – forming a V-shaped groove known as the terminal sulcus. At the centre of this groove is the foramen cecum, a pit which represents the place of origin of the thyroid gland.
As the tongue forms, it is initially is tethered to the floor of the oral cavity. A process of carefully programmed cell death known as sculpting apoptosis releases the tongue, leaving in place the lingual frenulum to anchor the tongue in the mouth.
Occipital Somites (Musculature)
- The intrinsic and extrinsic muscles of the tongue are derived from occipital somites, which are segments of mesoderm in the region of the upper neck.
- The somites migrate from the neck anteriorly to give rise to the muscles of the tongue.
Development of the thyroid gland
- The thyroid gland begins development as a proliferation of endodermal cells between the cupola and tuberculum impar of the primitive tongue (the site of the future foramen cecum).- floor of the pharynx
- This proliferation of cells bifurcates and descends into the neck as a two-lobed diverticulum. By week 7, it has reached its destination in the anterior neck, and is formed of two lateral lobes connected by a central isthmus.
- The descent of the developing thyroid gland forms the thyroglossal duct – an epithelialised tract that connects the gland to its origin at the foramen cecum. It usually regresses by the 10th week of gestation but can persist in some individuals.
thryoglossal cysts and fistulae
- Ectopic thyroid tissue
Can appear anywhere along the path of descent
classic facial characteristic
small ehad
epicanthal folds- inner nose near eyes
small eay openings
low nasal bridge
short nose
thin upper lip
smooth philtrum
