3 - Face nose and ears dev. Flashcards by Tyler Brown

Most Facial structures develop during weeks

4-8 (or the second month)

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Week 4

Pharyngeal arches appear; formation if maxillary and mandibular processes; buccopharyngeal membrane breaks down

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Weeks 5-6:

Nasal placode invaginates to form the nasal pit, creating medial & lateral nasal processes; nasal pits deepen to form the nasal cavity

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Week 7

Facial swellings fuse to create the rudiment of the face; secondary palate is formed

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Week 10

Fetal development:

Cranium expands; ears move superiorly; eyes move medially; nose becomes more prominent; facial proportions normalize as acquire teeth & paranasal sinsues

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Fetal period

3 mo. To birth. Nose becomes more prominent and well defined.

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Balance in proportions occurs with

maxillary and mandibular development as well as the establishment of the paranasal sinuses

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Week 4: Facial Primordia

5 facial primordia develop as bulging prominences around the stomodeum:

Frontonasal prominence 
Maxillary prominences (2)
Mandibular prominences (2)

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Buccopharyngeal membrane separates the primitive oral cavity from the

developing gastrointestinal tract. In the early 5th week the buccopharyngeal membrane disintegrates.
(Oropharyngeal = buccopharyngeal = oral membrane)

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By the end of the second month we can

identify recognizable facial features.

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Cranium expands to accompany

growing brain, which causes eyes to shift anteriorly & medially

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Fetal Period

Ears move superiorly

Nose becomes more prominent

At first, facial skeleton appears small in comparison to rest of skull. Proportions become more normal once maxilla & mandible grow to allow space for teeth and once acquire paranasal sinuses

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Development of the Nose: Nasal Placodes

End of 4th week: 2 ectodermal thickenings develop within frontonasal prominence:
the nasal placodes

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Mesenchyme surrounding the placodes

proliferates, forming elevations:

Medial nasal prominences (2)
Lateral nasal prominences (2)

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Facial Development: Month 2-3

Facial features more pronounced, Eyes move medially

Ears move superiorly, 1st ossification centers in skull

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Beginning of month 3

limbs still small in proportion to body

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Both nasal pits deepen and expand dorsally into

nasal sacs, which will form the right and left nasal cavities

Week 5 (33-day embryo)

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Epithelium of nasal placodes sinks down into underlying

mesenchyme to form depressions: nasal pits (the future nostrils (nares))

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Nasal pits also appear to sink in due to

surrounding elevations (the medial & lateral nasal prominences)

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Both nasal sacs will form the

right and left nasal cavities

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Oronasal membrane separates

nasal cavities from oral cavity; ruptures at end of week 6. Nasal & oral cavities now in communication through primordial choanae

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buccopharyngeal membrane had disintegrated by the early part of the

5th week.

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Buccopharyngeal membrane disintegrates, then,

Oronasal membrane ruptures & disintegrates. (6th week)

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Nasal & oral cavities now in communication through

primordial choanae

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Development of secondary palate establishes the definitive

choanae separating nasal cavities from nasopharynx

Neuroectoderm gives rise to

Olfactory epithelium

Nasal conchae develop from

lateral walls of nasal cavity.

Mandibular prominences fuse at

midline first (day 28)

Maxillary prominences grow in size soon after

mand prominences fuse, move medially, compressing medial nasal prominences in midline

After compressed medial nasal prominences in mideline,

Medial nasal prominences fuse

Nasolacrimal Groove

Cleft between the lateral nasal prominences and the maxillary prominences: the nasolacrimal groove

The nasolacrimal groove is lost when

the lateral nasal prominences fuse with the maxillary prominences

Nasolacrimal Duct

Ectoderm proliferates into underlying mesenchyme & forms a solid rod that separates from surface & canalizes to become the nasolacrimal duct

Superior end of nasolacrimal duct dilates to form

nasolacrimal sac, and inferior end opens up into inferior meatus of nasal cavity

Medial nasal prominences fuse

intermaxillary segment:

Philtrum

of upper lip (labial component)

Premaxillary part of maxilla

(upper jaw component) – 4 incisors & associated gingiva

Primary palate

(palatal component; the 1° palate is only the most anterior portion of the hard palate)

Secondary palate

the remainder of the hard palate + the soft palate (+ uvula

Week 6:

Two plates of mesenchyme – lateral palatine processes – extend medially from the maxillary prominences

Palatine processes project inferomedially, then swing

upwards to assume horizontal position, and fuse with each other, with 1° palate, & with nasal septum

The palatal processes close by the end of the

10th week, but are fused by the 12th week.

Incisive foramen

marks where secondary palate fuses with primary palate; used to indicate anterior & posterior palatal defects

Median palatine raphe

marks where lateral palatine processes fused together

Primary palate and anterior portion of secondary palate will ossify forming

the bony hard palate

Posterior-most portion of the secondary palate does not ossify – extends

posteriorly to form the soft palate & uvula

Cleft Lip

An anterior palatal defect caused by failure of medial nasal prominences to fuse with maxillary prominences on one or both sides

Cleft lip can result in

cleft lip (unilateral, bilateral, or at midline), cleft palate (between primary and secondary palates)

Unilateral cleft lip & palate

Failure of MXP on one side to fuse with merged MNPs

Bilateral cleft lip & palate

Failure of MXPs on both sides to fuse with merged MNPs

Week 4: Inner Ear is the

first to develop

inner ear Develops as a

bilateral thickening in surface ectoderm at the level of the caudal hindbrain: otic placodes (2)

Ectoderm invaginates in each placode, forming an

otic pit, the edges of which pinch off to form an otic vesicle that separates from surface ectoderm --> will become the membranous labyrinth for each ear

Otic Vesicle is going to give rise to the

membranous labyrinth

Inner Ear Development - Diverticulum extends from

otic vesicle to form the endolymphatic duct & sac

Otic vesicle can be divided into two regions:

``` Utricular region (dorsal)  utricle + semicircular ducts Saccular region (ventral)  saccule + cochlear ducts ```

The cochlear duct grows out as extension from

saccular region and coils to form the membranous cochlea

Vacuoles develop in cartilage surrounding the

cochlear duct and unite to form the perilymphatic space (two divisions: scala vestbuli and scala tympani, both filled with perilymph

Cartilage surrounding cochlear duct ossifies to form

the bony labyrinth encasing the inner ear structures

The cochlear duct grows out as extension from

saccular region and coils to form the membranous cochlea

Cells in walls of coiled duct form the

spiral organ of Corti

Cell bodies of CN VIII migrate along coils of

cochlear duct and form the spiral ganglion

External Ear: Auricle (Pinna) develops from

auricular hillocks: mesenchymal proliferations surrounding the 1st pharyngeal groove (mesenchyme from 1st & 2nd pharyngeal arches)

Auricles develop at level of

1st pharyngeal groove. Auricles will shift to final position (eye level)

Optic Vesicles -->

Optic Cups & Optic Stalks

Lens development -->

Lens placode --> Lens pit

Remember that the lens is derived from the invagination of

surface ectoderm.

Hyaloid canal remains as a space left in the

vitreous humor

Distal portions of the hyaloid a. & v.

degenerate - note that the hyaloid v. is not shown in all of the depictions.

Central retinal a.

(incorporated into optic n.)

Coloboma

“Key hole” appearance of the iris due to failure of the retinal fissure to close in the 7th week

Iris

from neural crest

Pupillae mm

from neuroectoderm

The iris forms from

mesenchyme (migrated neural crest)

Development of the Cornea - lens induces

cornea

Corneal Layers

outer: ectoderm | middle & inner: mesenchyme (migrated neural crest)

Eyelids are from

From mesenchyme (migrated neural crest)

Eyelids are fused

weeks 8-27; Open in the 28th week

While the eyelids are adherent, there is a closed

conjunctival sac anterior to the cornea.

Placode

thickening of ectoderm

Stomodeum

primitive mouth

Mitral cells

in olfactory bulb

Bipolar cells

CN1

Nerves and vessels form

before bone

Retinal fissure

Opening to allow for vasculature to supply developing eye

Cornea

inner and outer layer - outer is completley continous with surface ectoderm, inner continuous with sclera

Ciliary body

comes from choroid and neural retina components

Cells of ciliary process produce

aqueous humor