L1 Flashcards
During fourth embryonic week
Merging, not
Note: merging, not fusing, takes place between facial processes.
4th embryonic week: The groove seen in the image between maxillary and median nasal processes is gradually
eliminated
If the maxillary process or processes do not merge with the median nasal process by the 5th embryonic week,
unilateral or bilateral clefting of the upper lip occurs
Although rare, if the mandibular processes do not merge with each other by the 5th embryonic week,
clefting of the lower jaw occurs
End of week 4: Groove between
median and maxillary processes is still evident:
its length is lessened and median process is narrower
Merging of facial processes complete by
y 5th embryonic week. If merger is not completed by this week, facial clefts occur
Review of the fate of the 3 boundaries of the stomodeum:
Frontal prominence:
after the appearance of nasal pits becomes:
* right and left lateral nasal facial processes
* median nasal facial process
Review of the fate of the 3 boundaries of the stomodeum:
Cardiac plate:
*replaced by the mandibular facial processes during 4th week IU
Review of the fate of the 3 boundaries of the stomodeum:
Buccopharyngeal membrane
*ruptures in 4th week allowing opening to the foregut that becomes the nasal and oral pharynx
Note: the buccopharyngeal membrane is the site of the pillar of fauces
Boundaries of Stomodeum (S):
3rd embryonic week
Superior: 1 = Frontal prominence
Inferior: 2 = Cardiac plate
Posterior 3 = Buccopharyngeal membrane
Tongue : Appearance and Formation during
fourth embryonic week.
Four lingual swellings appear during the 4th embryonic week along the ventral, inside surface
of mandibular process of branchial arch I, II and III. During this same 4th week the buccopharyngeal membrane ruptures and, the 4 lingual swellings merge to become the t o n g u e
Fate of 4 lingual swellings during 4th embyronic week:
Position of the 4 lingual swellings along the front wall of the pharynx and their
contributions to the t o n g u e:
Tuberculum Impar and 2 Lateral lingual swellings become anterior two - thirds of tongue
Copula becomes posterior third or root of tongue
Copula becomes
posterior third or root of tongue
The stomodeum will begin to partition
into oral and nasal cavities in the following
6th embryonic week:
Fifth Embryonic Week
Appearance of structures within the stomodeum that enter into formation of palate:
Primary palate: Nasal septum: Palatine folds or shelves:
Primary palate arises from
inner surface of median nasal facial process
Nasal septum arises from
primary palate
Palatine folds arise from
inner surface of maxillary facial processes
Outer surface of median facial process become what parts of face?
Frontal: note vertical position of palatine folds or shelves lateral to tongue
Outer surface of maxillary processes become what parts of face?
Axial
Tongue appears in what embryonic week ?
4th
Primary palate:
inner surface of median nasal process:
median nasal process gives rise to the nasal septum
Palatine folds or shelves: arise from
medial or stomodeal surfaces of maxillary processes
Histologic: Frontal view
Fifth embryonic week
The palatine folds or shelves, that arise from the inner surfaces of the
maxillary processes, are vertical in position on either side of the tongue
The palatine folds or shelves have
lining epithelium that is connected to an underlying
mesenchymal tissue also called ectomesenchyme (originates in ectoderm primary germ layer)
5th week Palatine folds move from a vertical position to a
horizontal position above the tongue:
Cecum
blind duct
Fifth Embryonic Week:
Frontal: palatine folds in
horizontal position above tongue
B Looking up: position relationships of anterior of palatine folds with primary palate:
The edges of these structures outline the letter ‘Y’
Mesenchyme tissues of the palatine folds and nasal septum flow
toward each other:
Structures that fuse to form the palate:
PP = Primary palate
N = Nasal septum
PF = Palatine folds
Note again ‘Y’ outline at edge of structures
Palate: Epithelial Fusion:
Begins in the
sixth embryonic week with the epithelial fusion of:
primary palate (PP) with palatine folds (PF) (arms of the ‘Y’)Epithelial fusion progressing
posteriorly:
epithelium of palatine folds fuse with each other
and with epithelium of nasal septum
A: Palatal view of:
Initial Fusion between:
Primary Palate(PP) and
Palatine Folds (PF)Note: most of fused epithelial cells undergo
cell death, some remain within the mesenchyme, as epithelial rests
Axial views: Stages of (secondary) palate formation
Epithelial fusion and mesenchymal union occurs between
6 and 8 weeks IU +
Formative stages of oral and nasal cavities: (E)
stomodeum no longer present
Oral cavity view of palate
Epithelial fusion line and area of mesenchymal union between palatine folds and primary palate
( between 6 to 8 weeks IU+)
Note that the fusion line is in the shape of a Y : Arms of Y is fusion of anterior ends of palatine folds with primary palate: Stem of Y is fusion of palatine folds with each other and above (not seen) with the nasal septum.
Formation:
an organization level involved in the growth and development of an organ and an organism.
(The way a particular spatial arrangement (shape) of something occurs)
Growth:
increase in weight and spatial dimensions (shape) that an organ and organism undergoes
Development:
the growth of an organ or organism through various formative stages on its way to maturation
Third embryonic week: Crown- rump measurement
3mm
(Note: In the 8th week in utero, start of fetal stage,
crown-rump measurement is 30 mm)
The stomodeum (stomatodeum) is a depression between the brain (A) and the
pericardium (B) in an embryo; it appears in the third embryonic week and becomes the nasal and oral cavities between 6th and 8th embryonic week. And gives rise to Rathke’s pouch ®, precursor of the anterior lobe of the
pituitary gland.
Boundaries of stomodeum
Superior: Frontal prominence
Inferior: Cardiac plate (swelling)
Posterior: Buccopharyngeal membrane
The branchial arches and clefts, as such, appear and disappear in the
fourth embryonic week In this week:
Arch I becomes right and left maxillary facial processes and right and left mandibular facial processes:
Some of the mesenchymal tissue in the branchial arches
originates in the
ectoderm germ layer and thus is called ectomesenchyme*
Ectomesenchyme has similar properties to
mesenchyme. The major difference is that ectomesenchyme arises from
neural crest cells which are a group of cells that arise from the ectoderm germ layer and form in the cranial region during early development. Ectomesenchyme plays a critical role in the formation of the hard and soft tissues of the head and neck, such as bones, muscles and tooth tissues: (dentin, cementum, pulp)
The place where the upper maxillary and lower mandibular processes meet at
either side of the stomodeum becomes the
commissura labiorum oris
The 2 Mandibular facial processes replace the
cardiac plate as the lower boundary of the stomodeum,
the 2 Maxillary facial processes become the posteriolateral boundaries of stomodeum
Nasal pits appear within the
frontal prominence: After appearance of nasal pits, the frontal prominence becomes three (3) facial processes:
Median Nasal facial process and a Right and a Left Lateral Nasal facial process
replacing the frontal prominence as the superior boundary of the stomodeum
Nasal pits deepen and become
nasal ducts that open into the stomodeum.
The ducts become nostrils that open into nasal cavities during
formation of nasal and oral cavities
Frontal prominence becomes 3 of the 7 facial processes:
Right and left lateral nasal process (2)
Median nasal proces (1)
Paired branchial arch I beome 4 of the 7 facial processes:
Right and left maxillary processes (2)
Right and left mandibular processes (2)
Median Nasal Process
Becomes:
- midline of nose
* philtrum of upper lip
Lateral Nasal Processes
Become
- lateral sides and ala of nose
* infraorbital part of face
Median and lateral nasal facial processes arose
from what structure that was present in the 3rd week IU?
Frontal prominence
Maxillary Processes:
Become:
- upper part of cheeks
* lateral parts of upper lip
Mandibular Processes:
Become:
- lower part of cheeks
- lower lip
- chin
Maxillary and Manibular processes arose
from what basic structures?
Branchial arch I
How many processes form upper lip =
3.
How many processes form lower lip =
2.
How many processes for cheeks =
4.
7 overall processes for
face.
Each Arch I becomes 4 facial processes:
2 maxillary, 2 mandibular
Each Cleft I becomes the external auditory meatus
Each Arch II becomes an emrbyonic fold of tissue called:
o p e r c u l u m: (cover)
The operculum covers Arches III and IV and Clefts II, III, IV
The operculum becomes sides of neck below external auditory meatus
Branchial cleft I becomes
external acoustic (auditory) meatus Each second (II) branchial arch elongates as an embryonic fold, the operculum, that overlaps clefts II and III, and arches III and IV to become the sides of the neck
