3/6/2009
The beginning thru week one
Embryology
Woman’s ovum fertilized
by man’s sperm forming
a zygote
Zygote undergoes mitosis
t form
to
f
a hollow
h ll off cells
ll
called a blastocyst
Development of the Head and Neck
The blastocyst becomes
implanted in uterus
A placenta and umbilical form
allowing passage of bloodborne
substances from mother to embryo
Embryonic second week
Embryonic third week
Ectoderm
Ectoderm
Mesenchyme
(mesoderm)
Endoderm
Blastocyst becomes embryo
during this period, is an
embryo for eight weeks
During second week, cells proliferate
and the ball shaped embryo becomes a
flattened bilaminar disc of ectoderm and
endoderm (an oreo cookie with NO filling)
Things to Remember
Endoderm
Bilaminar disc becomes trilaminar when mesenchyme
is formed in between two layers (an Oreo cookie WITH filling)
Mesenchyme generates connective tissue forming cells
(fibroblasts, osteoblasts) as well as another germ layer
called mesoderm
Ectodermal Dysplasia
• Ectoderm forms nerves, skin, hair, glands, enamel
of teeth
• Mesoderm forms muscles, bones, blood vessels,
connective tissue, dentin and pulp of teeth
• Endoderm forms respiratory and digestive system,
liver, pancreas
Predict what would occur if a person had the condition
ectodermal dysplasia?
Ectodermal dysplasia: complete or partial anodontia,
absence of hair, sweat glands, melanin
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Embryonic third week - Disc
Disc develops a depression called a
“primitive streak” dividing the disc
into left and right
•
•
•
•
•
•
Caudal end
Disc also forms a caudal end (tail)
And cephalic end (head)
right now the
Embryo is the size
of a pinhead
Steps in tissue formation
Primitive streak
ectoderm
Cephalic end
Mesenchyme
(mesoderm)
endoderm
Teratogens
• A teratogen is any substance, agent,
chemical, etc that causes abnormal fetus
development
• Examples of teratogens are radiation,
alcohol, cocaine, microorganisms, etc
• If several abnormal affects occur together,
it’s called a “syndrome”
Induction: The beginning
Proliferation: multiply
Histodifferentiation (cell type)
Morphodifferentiation (shape)
Apposition
Maturation
PREDICT what would happen if a disturbance occurs
during any of these steps.
Congenital syphilis
Hutchinson’s incisors
Mulberry molars
PREDICT the term used to describe this underformation
of tooth structure.
hypoplasia
Neuroectoderm – third week
Neuroectoderm forms
neural crest cells that
migrate to mesoderm,
help form brancial arches
pulp, dentin, PDL
Ectoderm differentiates
into neuroectoderm,
forms neural tube (spine)
Somites – third week
Somites appear as bulges
beside neural tube, somites
will develop into bones,
muscles, blood vessels, etc
Mesoderm differentiates into 38
pairs of somites
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Fourth week – embryonic folding
Neural tube
somites
Embryo – tube shape
At cephalic end, orophryngeal membrane fills gut,
temporarily closes off forgut. This membrane is the
posterior boundry of the stomadeum (primitive mouth)
endoderm
ectoderm
mesoderm
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How the embryo actually appears at four
weeks
Stomodeum
Face/neck development (during fourth week)
Six phryngeal (brancial) arches
appear- develop into part of face,
hyoid bone, pharynx
Right now, embryo is about
the size of a small pea
Mandibular arch (1st brancial
arch) gives rise to mandible,
part of maxilla
maxilla, upper lip
lip, all
teeth
B
Brancial
i l Arches
A h
Mandibular arch starts off as
Meckel’s cartilage
5th cranial nerve (trigeminal)
associated with 1st brancial
arch structures
Face/neck development (during fourth week)
2nd brancial arch starts as
Reichert’s cartilage
Face development (during fourth week)
Stomodeum
Reichert’s cartilage gives
rise to muscles of facial
expression, others
Frontal (frontonasal) process
Maxillaryy pprocess ((develops
p from
Mandibular arch)
Cranial nerve 7 (facial
nerve) associated
with 2nd brancial arch
Brancial arches 3 – 6 form
hyoid bone, pharynx, etc.
hypoglossal, glossophryngeal
nerves associated
Face development (during fifth week)
Frontal process growing downward,
will form middle of upper lip
(intermaxillary process)
Maxillary process growing toward
midline, will form sides of
upper lip
1st brancial (mandibular) arch
2nd brancial arch
Frontal view
Face development (during fifth week)
Optic placodes forming, will
begin moving toward midline
Nasal placodes form
Mandibular arch fused at midline
2nd brancial arch forming facial
muscles
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Face development (during sixth week)
Medial nasal process (philtrum)
contacts maxillary process
(site of cleft)
Face development (during seventh week)
Median nasal process and
Maxillary process fully fused
Face taking on human
appearance
llateral
t l nasall process forms
f
side
id
of nose
Auricular hillocks form
Nasolacrimal groove forms
PREDICT What would happen if
fusion of median nasal process and
maxillary process does not occur?
Lip Pits
Cleft Lip
Median nasal processes
Intermaxillary segment
Maxillary process
PREDICT in which week of
development a disturbance
occurred that caused cleft lip?
4 Types of Cleft Lips
• 1) Unilateral failure
of maxillary process
on 1 side to meet &
fuse w/ medial nasal
process, which results
in a division of lip.
Nasal distortion results
2) Bilateral
• Same but on both
sides
id
• Both unilateral &
bilateral may/or may
not be associated
w/cleft palate
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4 Types of Cleft Lip (cont)
3) Median Cleft Lip
• Extremely rare; partialcomplete failure of medial
nasal processes to merge.
merge
• Only one that can be
called a “hare lip”.
Derived from rabbits-have
a cleft in middle of lip
Neck development (during seventh week)
Only 1st brancial groove forms
a structure, external auditory
meatus
Phryngeal pouches develop in
conjunction with arches, grow
toward midline, form many
neck structures
4) Median Cleft of Mandible
• Rare condition
• Failure of mesenchymal masses of
mandibular processes to merge together at 5
wks
• Dimple of chin is slightest form of
incomplete merging of the 2 mandibular
processes
Palate development – seventh thru eleventh week
Primary palate (premaxilla)
From intermaxillary segment,
contains maxillary incisors
Palatal shelves from
maxillary
ill
process grow
across, fuse at midline,
Form the secondary palate
PREDICT what would happen if palatal shelves
did not fuse?
http://www.med.unc.edu/embryo_images/unithednk/hednk_htms/hednktoc.htm
Cleft Palate
Primary palate formed
(no cleft lip)
Palatal shelve fusion
forming secondary palate
did not occur
Nasal cavity
PREDICT in which week of development a
disturbance occurred that caused cleft palate?
7th – 9th week
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Classifications of Clefts
• Class 1- Cleft of the tip
of the uvula
• Class 2- Cleft of the
uvula (bifid uvula)
Classification of Clefts
• Class 4- Cleft of the
soft and hard palate
Classification of Clefts
• Class 3- Cleft of the
soft palate
Classification of Clefts
• Class 5- Cleft of the
soft & hard palates
that continues through
alveolar
l l ridge
id on one
side of premaxilla;
usually associated
with cleft lip of same
side
Classifications of clefts
• Class 6- Cleft of soft
& hard palates that
continues through
alveolar
l l ridge
id on both
b h
sides, leaving a free
premaxilla; usually
associated with
bilateral cleft lip
• Class 7- Submucous cleft in which muscle
union is imperfect across soft palate. The
palate is short;; uvula is bifid;; a groove
p
g
is
situated at midline of soft palate; and
closure to pharynx is incompetent.
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Tongue development
The Tongue
Body of tongue
Base of tongue
Body of tongue forms from three
parts, two laterals and central
tuberculum impar (mesenchyme
from 1st brancial arch)
Base of tongue formed from
mesenchyme
h
off 22, 3rd and
d 4th
arches (precursor is called the
copula).
Body of tongue
separated from base by
terminal sulcus
Tongue development
Body of tongue
Taste buds
Thyroid tissue forms at foramen
caecum, migrates to location
in neck following thyroglossal
duct
Base of tongue
Taste buds from epithelium
Innervated by 7th nerve
ankyloglossia
Macroglossia
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Cysts
During embryonic development if clumps of epithelial cells
(epithelial rests) get trapped and left behind, they may later
grow to form cysts
Lymphoepithelial
(Brancial cleft) cyst
Nasopalatine cyst
Thyroglossal track cyst
Median cysts
Globulomaxillary cyst
Median Mandibular cyst
At midline in mandible
Palatine
Always occurs between maxillary lateral and cuspid
Dermoid cyst
Nasolabial Cyst
Found in floor of mouth, cyst wall contains hair, sweat glands
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Pseudocyst – traumatic bone cyst
Pseudocyst – Stafne bone cyst
Pseudocyst - Aneurysmal bone cyst
Blood filled, spaces containing giant cells
Described as “honeycombed”, associated with trauma
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