ANA 307 Development of The Face Flashcards
When do facial developments occur?
Facial development occurs mainly between the fourth to eighth weeks.
At the end of the fourth week what occurs?
Facial prominences consisting primarily of neural crest-derived mesenchyme and formed mainly by the first pair of pharyngeal arches appear.
What are the facial prominanences?
The single frontonasal prominence
The paired maxillary prominences
The paired mandibular prominences
Discuss the paired maxillary and mandibular prominences
The paired maxillary and mandibular prominences are derivatives of the first pair of pharyngeal arches.
The paired maxillary prominences form the lateral boundaries of the stomodeum, and the paired mandibular prominences constitute the caudal boundary of the stomodeum.
Discuss the frontonasal prominence
The frontonasal prominence (FNP) surrounds the ventrolateral part of the forebrain, which gives rise to the optic vesicles that form the eyes. The frontal part of the FNP forms the forehead; the nasal part of the FNP forms the rostral boundary of the stomodeum and nose.
What occurs by the end of the 5th week
By the end of the fifth week, the primordia of the auricles (external part of the ears) have begun to develop.
Six auricular hillocks (three mesenchymal swellings on each side) form around the first pharyngeal groove (three on each side), the primordia of the auricle, and the external acoustic meatus, respectively.
Initially the external ears are located in the neck region however, as the mandible develops, they are located on the side of the head at the level of the eyes.
What occurs by the end of the 4th week
By the end of the fourth week, bilateral oval thickenings of the surface ectoderm,nasal placodes, have developed on the inferolateral parts of the FNP.
Initially these placodes are convex, but later they are stretched to produce a flat depression in each placode.
Mesenchyme in the margins of the placodes proliferates, producing horseshoe-shaped elevations-the medial and lateral nasal prominences.
As a result, the nasal placodes lie in depressions-the nasal pits. These pits are the primordia of the anterior nares (nostrils) and nasal cavities.
Proliferation of mesenchyme in the maxillary prominences causes them to enlarge and grow medially toward each other and the nasal prominences.
This expansion results in movement of the medial nasal prominences toward the median plane and each other.
Hence, the upper lip is formed by the two medial nasal prominences and the two maxillary prominence.
The lower lip and jaw form from the mandibular prominences that merge across the midline.
Each lateral nasal prominence is separated from the maxillary prominence by a cleft called the nasolacrimal groove.
Ectoderm in the floor of this groove forms a solid epithelial cord that detaches from the overlying ectoderm.
After canalization, the cord forms the nasolacrimal duct; its upper end widens to form the lacrimal sac.
Following detachment of the cord, the maxillary and lateral nasal prominences merge with each other.
The nasolacrimal duct then runs from the medial corner of the eye to the inferior meatus of the nasal cavity, and the maxillary prominences enlarge to form the cheeks and maxillae.
The nose is formed from five facial prominences which are:
The nose is formed from five facial prominences:
the frontal prominence gives rise to the bridge
the merged medial nasal prominences provide the crest and tip
the lateral nasal prominences form the sides.
The intermaxillary segment gives rise to what?
Phitrum of the lip
premaxillary part of the maxilla, that bears the upper 4 incisors and associated gums
Primary Palate
Discuss the secondary palate
The secondary palate is the primordium of the hard and soft palate
it begins to develop early in the sixth week from two mesenchymal projections that extend from the internal aspect of the maxillary prominences
List the development of the palate
Inter-maxillary process
Palatine processes of maxillary process maxillary process
primary/primitive palate
fusion of primary palates with palatine processes of maxillary process
fusion of pallets in processes in the midline
Secondary palate
philtrum
maxilla with 4 incisors
Describe the DEVELOPMENT OF NASAL CAVITIES
•During the sixth week, the nasal pits deepen considerably, partly because of growth of the surrounding nasal prominences and partly because of their penetration into the underlying mesenchyme.
•At first, the oronasal membrane separates the pits from the primitive oral cavity by way of the newly formed foramina, the primitive choanae.These choanae lie on each side of the midline and immediately behind the primary palate.
•Later, with formation of the secondary palate and further development of the primitive nasal chambers, the definitive choanae lie at the junction of the nasal cavity and the pharynx.
Paranasal sinus
Some paranasal sinuses begin to develop during late fetal life, such as the maxillary sinuses; the remainder of them develop after birth. They form from outgrowths or diverticula of the walls of the nasal cavities and become pneumatic (air-filled) extensions of the nasal cavities in the adjacent bones, such as the maxillary sinuses in the maxillae and the frontal sinuses in the frontal bones. The original openings of the diverticula persist as the orifices of the adult sinuses.
