Exam 1 Flashcards
No ameloblasts = no ______
enamel
There are X # of crystals per ameloblast
one
Since ameloblasts are lost after eruption enamel … 1) 2)
1) has to be the hardest tissue
2) can not regenerate
What %organic and %inorganic component is enamel
organic= 4% Inorganic= 96% (mineral)
enamel can not be regenerated but it can be ___ (to a certain extent
remineralized
Between dentin and enamel, which material can be repaired?
Dentin. Enamel can NOT be repaired.
What are the inorganic components that make up enamel?
- crystalline calcium phosphate (hydroxyapatite) subsatued with carbonate
- ions such as strontium, Mg, Pb, fluoride
What structure helps maintain hard brittle enamel?
a resilient underlying dentin
What will likely happen to enamel if underlying dentin is lost?
Will easily fracture, its hard but very brittle
What color is enamel
translucent, light yellow to gray-white
What are the various thickness of enamel?
max 2.5mm(working surfaces) to a thin featheredge on cervicle line
how does enamel differ from other hard tissues? 8 things
1) there is no pre-enamel (unlike dentin, bone, cementum)
2) crystals grow against the secretory surface of ameloblasts
3) enamel proteins do not play any major structuring function
4) enamel is already 30% mineralized when its being layed down
5) elasticity
6) color
7) no matrix vessicles
8) enamel lacks mineral modulating molecules (promoters and inhibitors)
What are the fundamental similarities between enamel and other hard tissues?
1) composed of hydroxyapatite crystals
crystalline calcium phosphate substituted with carbonic ions
Enamel crystals are organized into 2 units called ____.
Rods and interrods
Crystals are ____ shape in cross-section and run in a _____ direction along rods.
1) hexagonal
2) longitudinally
In regards to rod organization, name 2 characteristics regarding geometry and shape.
1) not a regular geometry
2) cylindrical
How does interrod enamel compare to rod?
Interrods have the same crystal morphology, but a different orientation.
What is found in the interface between rod and interrod enamel?
an organic sheath
Rods and interrods are closely packed and long ribbon-like carbanoatoaptite crystals measuring what width and thickness?
width: 60-70nm
thickness: 25-30nm
How does the structure of enamel change as it matures?
1) crystals become thicker
2) crystals have a different orientation
3) become more hexagonal
4) linear pattern can be seen in older crystals due to reflection of crystalline lattice (artifact)
What is the zone of confluence?
areas that crystals from interrod enamel enters the rod.
young enamel is a _____ texture compared to mature enamel
younger enamel is a uniform texture, has no rod sheaths
What are two steps that occur during mineralization?
1) crystals grow wider and thicker
2) phenotypic changes occur in ameloblasts
What are the phenotypic changes of ameloblasts
1) presecretory ( morphogenetic & histodifferentiation)
2) secretory
3) maturation
When does amelogenesis begin?
After a few microm of dentin is deposited at the DEJ
What happens during the presecretory stage of amelogenesis?
Cells differentiate, acquire phenotype, change polarity, develop and extensive protein synth machinery, prepare to secrete an organic matrix of enamel.
1) morphogenetic stage
2) histodifferentiation
What happens in the morphogenetic stage of amelogenesis?
the shape of the crown is determined
What happens during the histodifferentiation stage of amelogenesis?
cells of the inner dental epithelium are differentiating into ameloblasts
The presecretory stage starts from what are of the developing tooth?
starts from the cusp tip outlines
Describe the secretory stage of amelogenesis.
Ameloblasts elaborate and organize entire enamel thichkness.
Tomes processes develop at apical end of ameloblasts.
Amelogenin accumulates.
What is Tomes processes?
Short conical processes that develop at the apical end of the ameloblast.
What is the main protein that accumulates during amelogenesis? And at what stage?
Amelogenin, secretory stage
Name two main things that happen during the Maturation stage of amelogenesis.
1) transportation of ions
2) mineralization
How do ameloblasts contribute to maturation?
1) modulate and transport ions
2) become more active in absorption of water and organic matrix-contributes to mineralization phase
3) secrete an organic cuticle on the surface of enamel= primary cuticle
What is a primary or developmental cuticle
an organic cuticle on the surface of enamel formed by ameloblasts after they have completed their contributions to the mineralization phase.
The protection phase of amelogenesis is characterized by…
1) ameloblasts are shorter
2) ameloblasts contact the stratum intermedium and outer dental epithelium
3) The above fuse to form the reduced dental epithelium
4) when tooth erupts the reduced enamel epithelium is destroyed, but the cervical parts become the junctional epithelium
How is junctional epithelium formed and where?
As the tooth erupts the incisal part of the reduced dental epithelium is destroyed, but the epithelium present cervically interacts with oral epithelium to become junctional epithelium.
Ameloblasts can be described as what type of cell?
Tall columnar
What happens to ameloblast’s nuclei?
Reverse polarization
The initial layer of enamel is ____.
Rodless, but composed of interrods that extend to make a honeycomb like structure. End layer of enamel is also rodless.
Which way do ameloblasts move in reference to the dental papilla?
Ameloblasts move away from dental papilla, causing a change in vascular supply.
What happens after full thickness formation?
1) maturation of enamel starts
2) ameloblasts shorten
3) loss of distinct layers of dental organ
4) blood vessels invaginate but dont violate papillary layer
What happens when enamel is fully mature?
ameloblastic and papillary layers become reduced enamel epithelium
What does the reduced enamel epithelium do?
1) protects enamel from follicular cells
2) helps form the junctional epithelium
Describe the life cycle of ameloblasts in 7 steps.
1) morphogenic
2) histodifferentiation
3) initial secretory stage (no tomes’ processes)
4) secretory stage (tomes’ processes)
5) ruffle-ended ameloblast of the maturative stage
6) smooth-ended ameloblast of maturative stage
7) protective stage
What is modulation?
Going back and forth between the ruffle-ended emeloblast to the smooth ended ameloblast. Occurs during maturative phase.
Describe presecretory morphogenietic stage ameloblast cells.
1) cuboidal to lowpcolumnar
2) centrally placed nuclei
3) poorly defined golgi
4) cells can still divide
Describe what happens to ameloblas (cellularly) during presecretory histodifferentiation step. 8 things
1) elongation of cells
2) reverse polarization
3) breakup of the basal lamina
4) golgi apparatus moves distally
5) RER
6) development of tomes processes (proximal)
7) Cell division seizes!!
8) junctional complexes and terminal webs
What happens in the secretory stage of amelogenesis? 5 things
1) constitutive secretion (continuous, no storage of secretory granules)
2) proteins are released against the mantle dentin
3) mineralization starts concomitantly
4) tomes distal processes develop
5) formation of pit, interrod, and rod enamel
What happens to tomes processes during the secretory stage of amelogenesis?
they become longer and thinner, move distally (called Tomes distal processes)
What proteins are released against mantle dentin during secretory stage?
1) amelogenin (90%)
2) ameloblastin
3) enamelin
What happens to the basal lamina separating ameloblasts from predentin?
1) differentiating ameloblasts send cytoplasmic projections into it
2) basal lamina is fragmented and removed before active deposition of enamel matrix
Where do secretory granules of ameloblasts go?
- translocated into tome’s processes
- accumulate by secretory surfaces
- recognized by infoldings of membrane
What are the two parts of Tomes process?
1) proximal tomes process (ppTP)- extends from the junctional complex to the surface of the enamel layer
2) Distal tomes process (dpTP) penetrates into enamel.
Which of tome’s process is first present?
the proximal part of tomes process
the interrod growth site is associated with witch tome’s process?
the proximal portion of Tome’s crocess
Rod growth cites are associated with which part of Tome’s process?
the distal portion of tomes process
Where are secretory granules released?
the infoldings of tome’s processes
how long does maturation of newly formed enamel take?
4 years
what happens (ultrastructural) in maturation of amelogeneisis?
1) crystals mature, enlarge, harden
2) matrix proteins and fluid are replaced
3) apoptosis of ameloblasts start (enamel knot at cusp tip)
4) modulation
5) secretion of basal lamina material that adheres/protects enamel (hemidesmosomes)
What is the significance of modulation?
Maintaining an enviornment that allows for accretion of mineral content, and loss of organic matrix. Ph alters which facilitates the process.
What do ruffle-ended ameloblasts produce and why?
Produce bicarbonate ions to 1) protect enamel from decalcification
2) maintenance of pH for matrix degrading enzymes
3) pumping of calcium into enamel
What do smooth-ended ameloblasts do?
leak small proteins and water out of enamel.
Which form of ameloblast exists at low pH?
ruffled-ended ameloblasts @ ph 5.5
smooth-ended ameloblasts @ 7
What form (ruffled or smooth) do ameloblasts spend most of their lives in?
ruffled
what do ameloblasts secrete as they enter modulation stage?
basal lamina (nueva)
What do ameloblasts form in basal lamina nueva?
hemidesmosomes, laminin-5, amelotin, NO type IV collagen.
What are some characteristics of amelogenin proteins?
1) have several isoforms
2) present in both x & y chromosomes
3) undergo major and minor extracellular processing
4) epithelial mesenchymal events
What is the function of amelogenins?
controls growth in thickness and with of crystals by forming nanospheres.
What happens in loss of function of amelogenins?
enamel defects that affect overall thickness and enamel rod strucure
Name the disorder in which a patient does not form enamel rods and what protein is involved?
Hypoplastic amelogenesis imperfecta, amelogenins
What is the function of ameloblastin protein?
in newly formd enamel it helps stabilize the DEJ by adhering (secretory stage)
What results in loss of function of ameloblastin?
terminal differentiating ameloblasts detach from dentin and enamel formation is aborted
What is the function of the enamelin protein?
promotes crystal elongation
What is the result of loss of function of enamelin?
no defined enamel layer
What are three things amelotin protein is involved in?
1) modulating emeloblasts
2) basal lamina
3) junctional epithelium
2 things apin is associated with are…
1) modulating ameloblasts
2) calcifying epithelial odontogenic tumor
Name two proteinases of anamelogenesis.
1) enamelysin
2) kallikrein-4
What does enamelysin do?
cleaves ameloblstin and enamelin in the secretory stage- short term processing of enamel proteins
3 things about Kallikrein-4
1) serine proteinase
2) during modulation
3) loss of function = enamel hypomutation
loss of function of enamelysin =
formation of a thin hypomutated enamel layer….related to amelogenesis imperfecta hypomaturation type
When is kallikrein4 secreted and where?
secreted into full thickness enamel when ameloblasts loose their tomes processes and start their modulation cycle.
What is the function of kallikrein4?
slowly degrades residual amelogenins and framents from nonamelogenins
loss of function of kallikrein4 results in ___
hypomature enamel
Calcification mechanism: deposition of calcium salts on ____.
collagen fibrils
calcification is induced by.. 1__ 2___
1) high affinigy calcium binding proteins
2) proteoglycans
calcification is aided by ___
alkaline phosphatase
name 2 ways calcium moves from the blood?
through intercellular and transcellular routes
where do calcium crystallites form?
against mantle dentin
dentin may provide ___ for enamel crystallites.
nucleation (helps start crystal formation)
surface enamel is ____
most highly mineralized
what does the degree of mineralization do as it moves towrds the DEJ?
degree of mineralization decreases
mineralization _______ at the innermost layers
increases
what type of arrangement do rods have around the long axis?
circumferential
rods do not have a straight course except for where?
in the cervical, inner 2/3s adjacent groups intertwine
rods are oriented _____ to dentin surface
perpendicular with a slight inclnation toward cusp
what unique rod orientation is seen near the cusp tip?
gnarled enamel… vertical and twisted rods
rods are ____ at the cervix.
parallel
where do rods deviate in arrangement?
the CEJ
what are striae of retzius?
- ground sections of calcified teeth
- incremental lines or weekly rhythm of enamel production
what is a neonatal line?
an enlarged striae of retzius
accented striae of rezius could be cause by ___.
systemic disturbances.
what are perikymata and where are they found?
- endpoints of striae of retzius found on surace of enamel
- appear as shallow furrows, circumferentially horizontal lines
what are cross striations?
-changes in the organization of crystals
_structural interrelations of interrods and rods
describe bands of hunter-schreger
- an optical phenomenon when rods change direction
- seen in grounds sections, inner 2/3
- appears as light and dark zones
What are enamel tufts and where do they form?
greater concentrations of enamel protein that appear from the DEJ into the enamel a short distance.
-developmental
_branched
_no clinical significance
What are lamellae and where do they form?
- defects filled with organic material (trapped enamel organ or CT)
- form from surface to varying distances within enamel
- different from cracks
what are enamel spindles?
entrapped cytoplasmic processes of odontoblasts
-make a scalloped pattern
Name some changes enamel goes through with age.
1) lack of regeneration
2) enviornmental structural changes ex attrition, bruxism, abrasion
3) discoloration extrinsic and intrinsic
4) decreased permeability
5) progressive increase in Fl content
3 patterns of acid etching (dependent on crystal orientation)
Type 1- loss of rods
Type 2- loss of interrod enamel
Type 3- haphazard
acid etching can be done in which procedures?
fissure sealants, bonding, cementing, removal of plaque and increase of enamel porosity
Name an ex. of hereditary enamel defects
amelogenesis imperfecta
name 2 examples of developmental enamel defects.
1) hypoplasia caused by accidens, febrile disease, flurosis
- tetracycline staining
What does fluroide to to crystals?
makes them more resistant to acid dissolution by precipitating calcium phosphate
Name the process of tooth development
1) bud stage
2) cap stage
3) bell stage
4) Dentinogenesis
5) amelogenesis
6) crown formation
7) root formation and eruption
8) function
When does tooth development begin?
37 days of development
What is the primary epithelial band?
a continuous horseshoe-band of thickened epithelium in the location of upper and lower jaws, signifies the initiation of tooth development, forms the Buccal and Li vestibules
When/where does dental lamina appear?
Dental lamina appears as a thickening of the oral epithelium adjacent to condensation of ectomesenchyme. It begins to function in the 6th week of prenatal dev- contues to 15th yr after birth (3rd molars)
what is sucessional lamina?
lamina from which permanent teeth develop
Tooth development can be divided into 3 major stages…
1) bud stage
2) cap stage
3) bell stage
Describe bud stage.
characterized by rounded, localized growth of epithelium surrounded by proliferating mesenchymal cells, wich are packed closely beneath and around epithelial buds.
Describe the enamel organ in bud stage.
in bud stage the enamel organ consists of peripherally located low columnar cells and centrally located polygonal cells.
Describe cap stage.
- Condensation of the ectomesenchyme next to the tooth bud (caused by a lack of extracelluar matrix secretion by the cells, prevents separation)
- histodifferentiation begins at the end of cap stage
- epithelial outgrowth called enamel organ (will form enamel)
- dental papilla
Describe dental papilla in the cap stage.
ball of condensed ectomenenchymal cells
-will form dentin and pulp
Which cells differentiate into odontoblasts?
peripheral cells adjacent to the inner dental epithelium enlarge and differentiate into odontoblasts
What is the dental follicle or sac?
the condensed ectomesencymal tissue surroundign the enamel organ and dental papilla. It gives rise to cementum and the PDL.
Where do the PDL and cementum come from?
the dental follicle or sac
Describe lateral lamina.
An extension from the dental lamina that is connected to the enamel organ.
Describe an enamel niche.
An artifact produced during sectioning of the the tissue. Occurs because the enamel organ is in sheets rather than strands.
When are the inner and outer dental epithelium organized
cap stage
Describe an enamel knot.
A densely packed, nondividing accumulation of cells projecting from the inner enamel epithelium into the enamel organ. Exact role not known, maybe cusp develoment.
What is a dental organ or tooth germ?
A term used to constitute the structure that has enamel organ, dental papilla, dental follicle.
p21 gene expression is related to the appearance of what structure?
enamel knot precursor cells
Name two temporary structures that disappear before enamel formation begins.
Enamel knot and enamel cord
What are the functions of the enamel knot and the enamel cord?
Speculated that they are a resivor of dividing cells for the growing enamel organ.
Describe the bell stage.
- continuted growth
- enamel organ resembles a bell, deepening of the epithelium over the dental papilla.
- continuation of histodifferentiation
- *beginning of morphodifferentiation.
What is morphodifferntiation and when does it begin?
when the tooth crown assumes its final shape, begins in bell stage
Describe the inner dental epithelium during early bell stage.
- short columnar cells bordering dental papilla
- will eventually become ameloblasts (by differentiating into tall columnar cells)
- exert an organizing influence on mesenchymal cells of dental papilla which later form odontoblasts
What cells form odontoblasts?
mesenchymal cells in the dental papilla
What cells become ameloblasts?
inner dental epithelium
Describe the outer dental epithelium during the early bell stage.
- cuboidal cells that cover the enamel organ
- organize a network of capillaries that will bring nutrition to ameloblsasts
- later laid in folds which work with papillae to supply nutrition for enamel organ
What structure forms between the folds of the outer dental epithelium?
The dental sac forms papillae that contain capillary loops that provide the enamel organ vascular supply
Describe stellate reticulum.
- star-shaped cells with processes
- present between outer and inner dental epithelium
- secrete GAGs
- support/protect delicate enamel organ
- not present in root portions
Describe stratum intermedium.
- cell layer between the inner dental epithelium and stellate reticulum
- have high alkaline phosphate activit
- help inner dental epithelium (ameloblasts) form enamel, needed for calcification of enamel
Describe dental papilla in the bell stage.
- differentiate into odontoblasts under the organizing influence of the epithelium
- are first a cuboidal shape then acolumnar form and aquire the specific potential to make dentin
- separated from the enamel organ by the membrana preformativa just before dentin is formed.
What is the membrana preformativa?
the basement membrane that separates the enamel organ and the dental papilla just before dentin is formed
describe the cervical loop
- area where the inner and outer dental epithelium meet at the rim of the enamel organ
- point where cells continue to divide until crown is full size
- after crown formation will give rise to epithelium for root formation*
- critical for root formation
What is the “zone of reflexion”?
AKA cervical loop
- point where inner and outer dental epithelium meet
- critical in root formation
Where is the enamel cord located?
extends between the inner and outter dental epithelium
-we dont know significance yet
define epithelial pearls or cell rests of serre and name their clinical significance.
- epithelial cells that remain from dental lamina and lateral lamina that should have disintegrated
- clinical sig: cysts will develop (eruption systs), may form odontomas or supernumery teeth
How is crown pattern determined & when?
- bell stage
- folding of inner dental epithelium
- halting of mitotic activity within the inner dental epithelium determines shape
Describe the vascular and nerve supply during tooth development.
- clusters of blood vessels in dental follicle and papilla
- coincide with position of root formation
- enamel organ is avascular
Describe the nerve supply during tooth development.
- initally in the dental follicle during bud to cap stage
- seen in dental papilla during dentinogenesis
- nerve fibers do not enter enamel organ
What is ameloblastoma?
- tumors of odontogenic epithelium that may arise from cell rests of enamel organ or the developing enamel organ or other things.
- histology resembles enamel organ epithelium with peripheral columnar ameloblast-like cells surroundign stellate-reticulum like cells
What is odontogenic myxoma?
- tumor of the jaw that arise from odontogenic ectomesenchyme
- histologically looks similar to mesenchymal portion of a developing tooth (dental papilla)
Describe the formation of the permanent dentition.
- successional teeth develop from further proliferative activity within the dental lamina, lingual to decidous tooth germ
- perm tooth develops lingual from deciduous tooth
Where does permanent molar development come from?
-originate from dental lamina that extends posteriorly beneath the oral epithelium after the jaws have grown
The entire primary dentition is initiated during which weeks of embryonic development.
6-8 weeks
When are successional permanent teeth initiated in utero and after birth?
-20wks in utero and through 10th month after birth
When are permanent molar initiated?
-between 20th week in utero (fist molar) and 5th year of life (third molar)
When does hard tissue formation start?
at the late stages of the bell stage
Which is formed first, dentin or enamel?
dentin
Which structure initiates the formation of enamel?
Dentin
Deposition of dental hard tissue is called ____.
apposition
Where does the first layer of dentin appear?
the cusp tips
After the first layer of dentin appears, which direction is dentin layed?
cervically
What happens to columnar cells of the inner dental dpithelium?
- they become elongated
- reverse polarization (nuclei adj to stratum intermediate
- become ameloblasts
The boundary between the odontoblasts and the inner dental epithelium will be the future ____.
DEJ
What is reciprocal induction?
- differentiating odontoblasts and ameloblasts will recieve signals from each other
- necessary for dentinogenesis and amelogenesis to take place normally
What are the stages of apposition?
1) Elongation of inner ental epithelium
2) Differentiation of odontoblasts
3) formation of dentin
4) formation of enamel
What type of collagen is found in dentin?
Type I
What is the fist layer of dentin called?
Mantle dentin
What happens at the same time or soon after mantle dentin is formed?
Inner dental epithelial cells differentiate into ameloblasts and secrete enamel proteins
How do enamel proteins effect ectomenenchymal cells odontoblasts.
Aid in terminal differentiation
Formation of enamel is called _____.
amelogenesis
What cells do odontoblasts come form?
ectomesenchymal cells of dental papilla (need influence from inner dental epithelium)
How are any acellular zones eliminated uring apposition?
increase in size of papillar cells (differentiating odontoblasts)
If there is no inner dental epithelium there is also no ____.
dentin (or enamel)
What does the inner dental epithelium secrete that effects the ectomesenchymal cells of dental papilla?
signalling molecules and growth factors
Odontoblasts are highly _____.
polarized
Which direction is the odontoblast nuclei polarized?
away from the inner dental epithelium
What composes mantle dentin?
- von Korff’s fibers (type III collagen fibrils)
- type I collagen
What are dontoblast processes or Tomes fibers?
- stubby processes on odontoblasts at the side closer to the inner dental epithelium
- extend into the extracellular matrix
- elongate and become active in dentine matrix formation
What is another name for dentine matrix?
predentin
How does predentin become dentin?
mineralization
Which direction do odontoblasts move as dentin is deposited?
towards the center of the dental papilla
What do odontoblasts leave behind as they move towards the center of the dental papilla?
cytoplasmic extensions that become surrounded by dentin
-forms a tubular structure
The 2 steps of dentinogenesis include:
1) formation of collagen matrix (predentin)
2) deposition of calcium and phosphate crystals (hydroxapatite) in the matrix
- similar to bone
Amelogenesis can be simplified into 2 steps:
1) production of a partially mineralized matrix (30%)
- second step involves influx of additional minearal coincident with removal of organic material and water to get 96% mineral content
What are tomes processes?
short conical processes that develop at hte apical end of the ameloblast
What is the difference between tomes fibers and tomes processes?
Tomes fibers: AKA odontoblast process. starts as a stubby process on an odontoblast that elongates and becomes active in dentine matrix formation
Tomes processes: short connical processes that develop at the apical end of ameloblasts
Where does growth occur on the developing crown?
- cusp tips
- intercuspal region
- cervical region
When does root development begin?
-After the enamel and dentin formation has reached the future CEJ
What is Hertwig’s epithelial root sheath?
- epithelial cells from the inner and outer dental ep cells at the cervical loop that proliferate to form the root(s)
- the root sheath determines if a tooth will have a single or multiple roots as well as their shape.
What are epithelial cell rests of malassez?
- fragments of root sheath that form discrete clusters
- persist in adults within the PDL adjacent to cementum
What is the epithelial diaphragm?
- the proliferating end of the root sheath bends at 45degree angle
- encircles the apical opeining of the dental pulp during root development
How do secondary apical foramens form?
-result of two or three tongues of epithelium growing inward toward each other resulting in multirooted tooth
What direction do roots grow?
Down, relative to the eruption of the crown
What also happens during root formation?
- tooth begins to erupt
- supporting structures (PDL, cementum) form
Which cells differentiate into cementoblasts?
-dental follicle cells that lie close to newly formed dentin
Which cells differentiate into the PDL fibers?
-cells of the dental follicle
Craniofacial defects as a result of damage during prenatal development would have to happen between which weeks?
4-8 weeks after fertilization
A ball of differentiating embryonic cells is called ___.
morula
How is a blostocyst different from a morula?
- morula grows into a blastocyst
- blastocyst has a primary yolk sac
- blastocyst has trophoblast and embroyblast layer
How many cell layers thick is the embryo during the 2nd week of gestation? What are these layers?
- 2 layers thick
- ectoderm and endoderm
- Called bilaminar germ disk
What forms the prechondral plate?
- a firm union between ectodermal and endodermal cells
- forms future head
How many layers thick is the embryo at 3 weeks of develoment?
- 3 layers, mesoderm formed
- called trilaminar embryonic disc
What does the primitive streak form?
-notochord
What is on either side of the notocord?
mesoderm
Name some major things that happen during the 4-8 weeks of development.
1) differentiation of major tissues and organs
2) differation of nervous tissue from ectoderm
3) differentiation of neural crest cells (ectoderm)
4) differentiation of mesoderm
5) folding of the embryo (2 plane- rostrocaudal & lateral)
What does the neural tube develop into?
forebrain, midbrain, hindbrain
what are somites?
segments of trunk paraxial mesoderm
Name the 3 components of somites.
1) clerotome- 2 adjacent vertebrae and disks
2) myotome- muscle
3) dermatome- connective tissue
What are somatomeres?
- fragments of paraxial mesoderm
- contributes to head and neck musculature
What does the intermediate mesoderm form?
urogenital system
What does lateral plate mesoderm form?
- CT of muscle and vicera
- serous membranes of pleura, pericardium and peritoneum
- blood and lymphatic cells
- cardiovascular system
- lymphatic system
- Spleen
- Adrenal cortex
What are rhombomeres?
- 8 bulges of hindbrain segments
- play an important role in development of the head
What is the buccopharyngeal membrane?
the structure that separates the stomatodeum from the gut
What is the stomatodeum and what is it lined with?
- a primitive oral cavity
- lined with ectoderm
What time frame does the embryo fold?
24 days to end of 4 weeks
The oral cavity originates from what type of tissue?
ectodermal tissue
The gut lining originates from what type of tissue?
endodermal
What are neural crest cells? What does it form?
- groups of cells that separate from the neuroectoderm, migrate, and differentiate
- form cranial sensory ganglia & most of the CT in the head
What do neural crest cells form?
- cranial and sensory ganglia and nerves
- adrenal medulla
- ectomesenchyme bone and skull
- dentin
- PDL
- alveolar bone
What does surface ectoderm form?
- epidermis
- hair
- nails
- cutaneous glands
- mammary glands
- anterior pituitary gland
- parenchyma of salivary gland
- enamel of teeth
- lense
- inner ear
What does neuroectoderm form?
posterior pituitary
pineal body
retina
CNS
What does the intermediate plate mesoderm form?
urogenital system
What does the paraxial mesoderm form?
muscles of trunk
skeleton except for skull
dermis of skin
CT (mesenchyme)
What direction do neural crest cells migrate?
laterally and forward
What is Treacher Collins Syndrome?
- defects of structures that are derived from te 1st and 2nd brachial arches
- due to failure of neural cress cell migration to the face region
- no mental handicap associated with the defect
What tissue is between the ectodermal and endodermal layers of the pharyngeal (branchial) arches?
lateral plate mesoderm
All arches have what type of tissue covering the outside (covers grooves)
ecotderm
What type of tissue lines the inside of the 1st branchial arch?
ectoderm
What type of tissue lines the inside of all but the 1st branchial arch?
endoderm
What is another name for the 1st brachial arch?
Mandibular arch
What is another name for the 2nd brancial arch?
hyoid arch
What is the fate of the 1st groove and pouch?
external auditory meatus tympanic membrane tympanic antrum mastoid antrum pharyngotympanic or eustachian tube *all related to ear
What is the fate of the 2nd, 3rd and 4th grooves?
they are obliterated by over growth of the second arch forming the cervical sinus
What happens if the cervical sinus persists?
branchial fistula that opens into the side of the neck extending from tonsillar sinus
congenital annomilie
What is the fate of the 2nd pouch?
obliterated by deveopment of palatine tonsil
What is the fate of the 3rd pouch?
dorsally- forms inferior parathyroid gland
ventrally- forms the thymus gland by fusing with counterpart from opposite side
What is the fate of the 4th branchial pouch?
dorsal: superior parathyroid gland
ventral: ultimobranchial body–> parafollicular cells of thyroid gland
What doe the 2nd and 5th branchial arch do?
grow towards each other to make branchial grooves disappear
What does each arch have?
cartilage
artery
nerve (motor and sensory)
The cartilage of the 1st arch is called ___.
Meckel’s
What is the cartilage of the 2nd arch called?
Reicherts
Some mesenchyme around arch cartilage gives rise to ___.
striated muscle
Sensory nerves from the branchial arches divide into 2 branches called ___.
1) postrematic branch: covers anterior half of the arch epith
2) pretrematic branch: covers the posterior half of the previous arch epithelium
What is Meckel’s cartilage relationship w/ developing mandible?
- indicates position of future mandible
- DOES NOT contribute to it
What type of ossification produces the mandible?
intramembranous ossification.
The malleus and the incus develop by ___.
endochondral ossification of the dorsal aspect of meckel’s cartilage
Meckel’s cartilage is associated with which CN?
CN V trigeminal
What develops from Reichert’s cartilage?
Dorsal end: stapes and styloid process
Ventral end: lesser horns of hyoid bone & superior part of the body of the hyoid bone
Reichert’s cartilage is associated w/ CN ___.
CN VII facial
What does the cartilage of the 3rd arch contribute to?
inferior part of the body and greater horns of the hyoid bone
What develops from the 4th and 6th arches fusing?
laryngeal cartilage
Name the nerve derived from the 1st (mandibular) arch.
Trigeminal CN V
Name the muscles derived from the 1st branchial arch.
muscles of mastication (temporalis, masseter, medial & lateral pterygoids) mylohyoid anterior belly of digastric tenor tympani tensor veli palatini
Name the skeletal structures derived from the 1st branchial arch.
malleus
incus
Name the ligments derived from the 1st branchial arch.
anterior ligament of malleus
spenomandibular ligament
Name the nerve derived form the 2nd branchial arch.
facial CNVII
Name the muscles derived from the 2nd branchial arch.
muscles of facial expression (buccinator, auricularis, frontalis, platysma, orbicularis oris and oculi)
stapedius
stylohyoid
posterior belly of digastric
Name the skeletal structures derived from the 2nd branchial arch.
stapes
styloid process
lesser horn of hyoid
upper part of body of hyoid bone
Name the ligaments derived from the 2nd branchial arch.
stylohyoid ligament
Name the nerve derived from the 3nd branchial arch.
glosspharyngeal CN IX
Name the muscle derived from the 3nd branchial arch.
stylopharyngeus
Name the skeletal structures derived from the 3nd branchial arch.
greater horn of the hyoid
lower part of the body of hyoid bone
Name the nerves derived from the 4th and 6th branchial archs.
superior laryngeal branch of vagus
recurrent laryngeal branch of vagus
Name the muscles derived from the 4th and 6th branchial archs.
cricothyroid levator veli palatini constrictors of pharynx intrinsic muscles of larynx striated muscles of esophagus
Name the skeletal structures derived from the 4th and 6th branchial archs.
thyroid cartilage cricoid cartilage arytenoid cartilage corniculate cartilage cuneiform cartilage
Aortic vasculature development: where are vessels in wk 4?
aortic vessels have passed through each branchial arch tissue and disappeared. pouches project laterally between each arch
Aortic vasculature development: where are vessels in wk 5?
-3rd branchial arch vessel becomes the common carotid which supplies the face by means of internal carotid and stapedial arterias
Aortic vasculature development: where are vessels in wk 7?
- prior to week 7: face,neck,brain supplied by the internal carotid
- Week 7: circulation to the face and neck switch from internal carotid to EXTERNAL CAROTID. Internal carotid still supplies the brain.
Which aortic arches disappear during development?
1,2,5
The vessel from arch 3 becomes what artery?
common carotid
The artery from arch 4 becomes what structure?
dorsal aorta
The artery from arch 6 becomes what vessels?
right and left pulmonary arteries
When do muscles in the 1st branchial arch become apparent? Spread to origin?
5th week become apparent
6th & 7th week migrate to origin
When do the muscles from the 2nd arch grow upward toward the face?
Week 7
Describe apparent fusion
fusion of facial processes by elimation of furrows
Describe true fusion
fusion of facial processes by breakdwon of surface epithelium
Muscles of the tongue come from
occipital somites
motor innervation does not come from branchial arches
Between which days of gestation does the face develop?
24-38th days
When does the 1st branchial arch divide into the mx and mn arches?
24th day
How is the middle portion of the upper lip formed?
By the fusion of the medial nasal process (both sides) with the frontal nasal process
How are the lateral portions of the upper lip formed?
fusion of mx process (each side) + medial nasal process
How is the lower lip formed?
by fusion of the two mn processes
how is the nasolcrimal duct formed?
fusion between lateral nasal process + mx process forming a canal
the pituitary gland is _____ in origin
ectodermal
The pituitary glad develops from what 2 ectodermal structures?
1) upgrowth from hypophysial diverticulum (rathke’s pouch)- adenohyopohysis, glandular
2) downgrowth from neuroectoderm of diencephalon called the neurohypophysial diverticulum- neurohypophysis, neural portion
What happens to the pituitary gland during the 4th and 5th week of development?
4th: hypophysial diverticulum (rathke’s pouch) projects from roof of stomatodeum, adj to diencephalon
5th: pouch elongates and is in contact with infundibulum
What do craniopharyngiomas devlope from?
remnants of stalk of hypophysial diverticulum
Overall the palate forms between ___ weeks.
7-9
When does the primary palate develop?
28 days of gestation
What structures does the primary palate develop from?
frontonasal and medial nasal processes
When does the secondary palate develop? Complete?
Develops between 7th, 8th week
Completes in the 3rd month
When is the critical period of palate development?
end of 6th week to beginning of 9th week
When does the tongue begin to develop?
4 weeks
What makes up the anterior 2/3 (oral part) of the tongue?
develops from 2 distal tongue buds (lateral swellings)
median tongue bud (tuberculum impar)
from 1st brachial arch
innervation: CN V
What makes up the pharyngeal part of the tongue? (posterior 1/3)
copula
hypobranchial eminence (2,3,4th arches)
innervation: CN
IX
What is the terminal sulcus?
line of fusion between the oral and pharyngeal parts of the tongue. Forms a V shape in adults
What is at the apex of the terminal sulcus?
foramen cecum
What nerve innervates the muscles of the tongue?
hypoglossal CN XII
When do the lingual papillae appear?
End of 8th week
When and how do tastebuds develop?
develop during 11-13th week by inductive interactions between epithelial cells of the tongue and gustatory nerve cells from corda typani, glossopharyngeal, vagus nerves
Which tastebuds appear first?
vallate & foliate
fungiform and filiform appear later
During which weeks does the thyroid develop?
4-7 weeks
What is a lingual thyroid?
A thyroid that did not migrate down to its normal place beneath the hyoid bone. Located in the foramen cecum area
What does the capsule of Meckel’s cartilage form?
sphenomandibular ligament
How many secondary sites of ossification are there for the devlopeing mandible?
3
Describe 4 important components in the timeline of the developing mandible.
1) mesenchymal condensation begins at wk 6
2) intramembranous ossification begins in the condensation at wk 7
3) rudimentary mandible is completed by 10wks
4) 3 secondary cartilages act as secondary centers of ossification, facilitate growth
Mandible development: when does mesenchymal condensation start?
6wks
Mandible development: intramembranous ossification begins in week ___.
week 7
Mandible development: When is the rudimentary mandible complete?
10weeks
Mandible development: what are the functions of the 3 secondary cartilages?
secondary centers of ossification that facilitate growth of mn until birth
In relation to Meckel’s cartilage, what direction does the mn grow?
laterally and anteriorlly
Name the 4 fates of Meckel’s cartilage.
1) posterior- malleus of inner ear
2) spenomandibular ligament
3) anteriorly, may contribute to mandible by endochondral ossification
4) remainder resorbed completely
Name the 3 secondary cartilages.
1) condylar cartilage: most important, develops at 12wks, remnant persists until 20yrs
2) coronoid cartilage- develops at 4 months
3) symphysial cartilage: develops as 2 independent cartilages near CT of Meckels
* all cartilages above are not part of meckel’s cartilage
Where does development of the Mx take place?
in the mx process of the 1st branchial arch from ONE center of ossification
What cartilage does the mx develop in close association wtih?
nasal cartilage
mx has no arch cartilage
What secondary cartilage contributes to mx development?
zygomatic cartilage
When does the mx sinus develop?
16 weeks
is small and rudimentary at birth
What intermediate structures of the tongue come from the 1st branchial arch.
median tongue bud
lateral lingual swellings
What adult structure does the median tongue bud form?
none- overgrown by lateral lingual swellings
What is the median tongue bud innervated by?
Li branch (sensory) of mn division of CN V
What adult structure does the lateral lingual swellings form?
mucosa of anterior 2/3 of tongue
What innervates the lateral tongue swellings?
corda tympani from CN VII
all taste buds except vallate papillae
What intermediate structures of the tongue develop from the 2nd branchial arch?
copula- it is overgrown by other structures in adults
What intermediate structure develops from the 3rd pharyngeal arch?
large ventral part of hypopharyngeal eminance
What does the large ventral part of the hypopharyngeal develop into?
mucosa of most of posterior 1/3 tongue.
the large ventral part of hypopharyngeal eminance is innervated by ___.
sensory branch of CN IX
also supplies valate papillae
What intermediate structure developes from the 4th pharyngeal arch?
small dorsal part of hypopharyngeal eminence, forms mucosa of small dorsal region of tonge as adult structure
What innervates teh small dorsal part of hypopharyngeal eminence?
superior laryngeal branch of vagus
Occipital somites form what intermediate structure of the tongue?
myoblasts
Myoblasts of the tongue form what adult structures?
intrinsic muscles of the tongue (XII) palatoglossus muscle (superior laryngeal branch of vagus)
