embryology 2012 [compatibility mode]

7/31/2019 Embryology 2012 [Compatibility Mode]

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EMBRYOLOGY

Jeremy Graham

26th March 2012

Learning outcomes

To describe the embryology of thehead region

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Pre-embryonic period (0-2 weeks)Fertilization

zygote, 0.1-0.2 mm

Cleavage divisions

Morula

(12-16 cells, 0.1-0.2 mm)

Blastocyst

32-200 cells, 0.1-0.2 mm

Inner cell massembryo proper

Outer cell mass =attachment

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Pre-embryonic period

Implantation

Endoderm

Ectoderm

Embryo is 2 layered disc0.1-0.2 mm

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Embryonic period (2-8 weeks)

Prochordal (cephalic) plate (PCP)

buccopharyngeal membrane(BPM)

future head end

Mesoderm (17 days)

ectodermal origin

Primitive streak and node

notochordal process

up to the PCPMesoderm separates ectoderm andendoderm, except in regions of:

PCP (BPM)

notochord

cloacal membrane

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Ten Cate

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Neural crest

Ectomesenchyme tissue

Dermis of head region

DENTINE

Branchial arches skeleton part of musculature

Pigment cells melanocytes

So far embryo is 1.5 - 3 mm

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Folding

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Development of the head and neck

BPM ruptures @ 21 days

stom(at)odeum (primitive mouth)

Branchial (or pharyngeal) arches

pharyngeal pouches

pharyngeal clefts

branchial from bragchia (Gk) gill whereas brachial means of the arm

Branchial arches

Each arch has cartilaginous rod, aortic arch artery, cranialnerve and branchiomere (muscle)

Nerves

1st arch: V

- 2nd arch: VII

- 3rd arch: IX

- 4th arch: X

Branchiomere

- 1st arch: muscles of mastication, tensors, MH

- 2nd arch: muscles of facial expression, SH


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Branchial arches

First or Mandibular ArchMeckels Cartilage

malleus and incus anterior ligament of the malleus sphenomandibular and other ligaments

Second or Hyoid ArchReicherts Cartilage

stapes

styloid process and stylohyoid ligament hyoid bone except greater horn

Third Arch- greater horn of hyoid

Tongue formation

From 1st, 2nd, 3rd (and 4th )branchial arches

appears @ 32 days

lateral lingual swellings (R and L)

tuberculum impar

copula

Innervation of tongueSensory

Anterior two-thirds of the tongue from 1st branchial arch, supplied by lingual n(V3)

Posterior third of the tongue from 3rd branchial arch, by glossopharyngeal n (IX)Tongue base from 4th branchial arch, by vagus n (X)

Taste

Anterior two-thirds of the tongue from 2nd branchial arch, by chorda tympani(VII)

Posterior third of the tongue from 3rd branchial arch, by glossopharyngeal (IX)- from 4th branchial arch, by vagus n (X)

Motor

Entire musculature hypoglossal (XII)

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Development of the face

Growth of

Mandibular processes(MDP)

Maxillary processes

Fronto-nasal process(FNP)


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Palate

1o palate and 1o septum

(FNP)- formed by 6th wk

2o palate and 2o

septum (Mx process)

@ 6 wks, 2 palatalshelves rise

by 12th wk, palatalfusion complete

Ectomesenchymal cells

inducing proliferation of

epithelial cellsTongue

Palatal Shelf

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Development of the jawsMaxilla

Intra-membranous ossification

2 ossification centresMaxilla proper

Premaxilla

ProcessesFrontal

Zygomatic

Palatine

Medial and lateral alveolar plates

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MandibleBody Meckels cartilage forms template

Mandibular nerve

Intra-membranous ossification starts@ 7 weeks

Medial and lateral alveolar plates

Ramus Secondary cartilages

Condylar cartilage appears @ 11 weeks

Coronoid cartilage

M.CTongue


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TIMELINE21 days: oropharyngeal membrane ruptures,

3mm long

23 days: branchial arches start to form

28 days: limb buds

32 days: tongue formation starts

5 weeks: nasal/optic placodes pits

6 weeks: mandibular processes fused in midline

primary palate and primary septumstart to bud (FNP)

6th week: secondary palatal shelves downwards(from maxillary process)

epithelial band develops

7th week: mandibular ossification commences

near mental foraminatongue fills oronasal cavityepithelial band into dental and

vestibular laminae

8 weeks: upper lip fused

8th week: palatal shelves horizontal sec.palate, by glycosaminoglycans (GAGs), tonguedropping, stomodeum

series of tooth buds off dental laminamaxillary ossification commencesabove #53-63 buds, near I/O foramen

11 weeks: condylar, coronoid and midlinecartilage (mnd)

11th week: cap stage

12 weeks: all palatal processes fused

12th week: late cap stage

14th week: early bell stage

15th week: dental lamina breaks down with

epithelium and b/n tooth germs

16 weeks: bones of palate start to fuse

permanent molar buds appear

18th week: late bell stage

20 weeks: mineralization starts in lwr deciduous

ants and lingual laminae of permanent incisors

embryology 2012 [compatibility mode]

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