Download Development of oro facial structures

Development of
oro - facial structures
By
jey
Introduction
• According to Todd – development is progress towards maturity
• According to Moyer's – development refers to all the naturally occurring unidirectional changes in the life of an individual from its existence as a single cell to its elaboration as a multifunctional unit terminating in death.
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Gametes are located in the sex organs ‐ Gonads Male gonad – testis
Female gonad – ovary
Spermatogenesis – formation of sperm in the testis
Oogenesis – formation of oocyte in the ovary
Gametogenesis – formation of sperm & oocyte
Introduction
• Development begins with fertilization
• Fertilization – is a process by which the male gamete the sperm, and the female gamete oocyte unite to form zygote.
Chromosomes •
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Human cell contain – 46 ch –
diploid
Autosomes – 44
Sex chromosomes or allsomes – 2 [x or y ]
In man ‐ 44 + xy
In women – 44 + xx
Gametes contain – 23 ch ‐ haploid
Introduction • Fusion of 2 cells with 46 ch is not possible
• If happens new cell will have 92 ch
• Thus require a cells with 23 ch [gametes], so that on fertilization cell with 46 ch will be reestablished
• Process of formation of gametes is called ‐
meiosis
Meiosis • Occurs in germ cells to generate male & female gametes
• Consists of 2 divisions
• At the beginning of meiosis duplication of DNA content takes place
• Stages – 1 division
• Prophase, metaphase, anaphase, telophase
• Prophase
• Leptotene – chromosomes become visible
• Zygotene – chromosomes pair each other – synapsis
Meiosis • Pachytene – chromosomes become distinct to form tetrad, crossing over of central chromatids occur – chiasma
• Diplotene – chromosomes move each other & change of genetic material occurs
• Metaphase1 – 46 chromosomes become attached to the spindle
• Anaphase1 – differs from mitosis here there is no splitting of Centromere & one entire chromosome of each pair move to each pole
• Other phases same as mitosis
Meiosis
Meiosis
Meiosis
I meiotic division
Random distribution of ch along with crossing over
Shuffling of genetic material
Cells with distinctive genetic content
Genetic shuffling in fertilization
No 2 persons are identical
Meiosis [clinical corelations] •
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Trisomy Monosomy Mosaicism Unbalanced trans locations
Structural abnormalities
Meiosis
Gametogenesis Ovulation Prenatal life
• Can be divided into
• I phase – comprises about 4 weeks, involves cellular proliferation, migration & some differentiation
• II phase – next 4 weeks, characterized by differentiation
• III phase – end of 2nd phase to the term, maturation & growth occurs
• I & II phase collectively called embryo
• III phase is called fetus
Formation of germ layers
Fertilization Events after fertilization
Cleavage Formation of blastocyst
Events during 1st week
Differentiation of ectoderm & endoderm
Formation of extra embryonic mesoderm
Formation of prochordal plate & primitive streak
Formation of intra‐
embryonic mesoderm
Formation of notochord
Formation of notochord
Formation of neural tube
Differentiation of mesoderm
Neural crest cells
Fate of germ layers
Folding of embryo
• Increased length of the disc causes it to bulge upwards into the amniotic cavity
• With further enlargement embryonic disc becomes folded on itself at the head and tail ends.
Folding of embryo
Effect of folds on positions of other structures
Pharyngeal arches
• After the establishment of head fold, foregut is bounded ventrally by the pericardium, dorsally by the developing brain.
• Cranially it is separated from the stomatodeum by the buccopharyngeal membrane. When this later breaks down, fore gut opens to the exterior through the stomatodeum.
Pharyngeal arches
• At this stage the head is represented by the bulging caused by the developing brain and the pericardium occupying the future thorax.
• These two are separated by the future mouth. this is apparent that the neck is not yet formed. • The neck is formed by the elongation of the region between the stomatodeum and the pericardium.
• However this elongation is achieved mainly due to appearance of series of mesodermal thickenings in the wall of the cranial most part of the foregut.are called the pharyngeal or branchial arches.
Pharyngeal arches‐coronal section
structure
Pharyngeal arches
Derivatives Nerves & muscles of arches
Fate of ectodermal clefts
Fate of ectodermal clefts
Fate of endodermal pouches
Clinical correlations of pharyngeal arches
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Ectopic thymic tissue
Ectopic parathyroid tissue
Branchial cyst and fistula
Disruption of neural crest cells results in – Trecher collin syndrome
– Perrirobin syndrome
Development of face
Development of face
Development of face
Development of face
Development of face
Development of palate
• Develop as primary & secondary palate
• Primary palate from fronto nasal process
• Secondary from maxillary process
• In the 6th ‐ palatine shelves grow obliquely on each side of tongue
• In the 7th week attain the horizontal position & fuse on the midline
Development of palate
Development of palate
Anteriorly the shelves fuse with triangular primary palate
• Incisive foramen is the midline landmark between primary & secondary palate
• The medial edges of palatine shelves fuse with the free lower edges of nasal septum –
separates the nasal cavity from oral cavity
• Later stages under go intramembranus ossification to form hard palate, does not extend posterior most part to form soft palate
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Development of palate
Development of palate
Clinical core relations
• Cleft lip – non fusion of maxillary with medial nasal process
• Cleft palate – non fusion of palatine process
• Oblique facial cleft ‐ non fusion of maxillary with lateral nasal process
Clinical co‐ relations
Clinical corelations
Development of tongue
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Develops in relation to pharyngeal arches
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Starts in the 4th week
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Lingual swellings – proliferation of medial most parts of the mandibular arches
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Tuberculum impar – partially separates lingual swellings
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Thyroglossal duct – formed behind the tuberculam impar, from which thyroid gland develops subsequently this site marked by depression called foramen cecum
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Hypobranchial eminence – another midline swelling in relation to 2nd, 3rd & 4th arches, shows cranial [copula] and caudal part
Development of tongue
Development of tongue
Development of tongue
Development of tongue
• Anterior 2/3s is derived from – I arch
• Posterior 1/3 is derived from – cranial part of eminence, here 2nd arch mesoderm gets buried, below the surface the 3rd
arch mesoderm grows over it to fuse with 1st
arch
• Posterior most part derived from 4th arch
Development of tongue
• Anterior 2/3s supplied by mandibular nerve, Posterior 1/3 is supplied by glossopharyngeal nerve & posterior most part by superior laryngeal nerve
• Musculature is derived from occipital myotomes – supplied by hypoglossal nerve
• Epithelium is first made up of single layer, later becomes stratified squamous & papilla become evident
Developmental anomalies of tongue
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Macroglossia
Microglossia
Aglossia
Bifid tongue
Ankyloglossia
Fissure tongue
Lingual thyroid
Molecular regulation of development
• By Homeobox genes
• First discovered in Drosophila in the year 1983
• Homeobox is conserved DNA motif of about 180 base pairs
• Homeobox encode for protein Homeodomain
• Homeodomain is DNA binding protein & regulate the transcription of other genes
Molecular regulation of development
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These genes are arranged in clusters
In drosophila – only one cluster & 8 genes
In humans – 4 clusters & 39 genes
They are called Hox genes present in 4 different ch
Molecular regulation of development
Molecular regulation of development
• Homeobox genes act in concert with other regulatory molecules – growth factors & retinoic acids
• Cells must express the receptors to have the effect of G F
• G Fs are two types – autocrine , paracrine
• Retinoic acids enter directly into the cell
Molecular regulation of development
Molecular regulation of development
• As indicated previously much of the face is derived from – neural crest cells
• Homeobox genes which regulate the facial development are carried to the pharyngeal arches by neural crest cells
Summary 2days
3days
4days
8days
14days
16days
Summary
17 days
22 days
21 days
4 & 5 week
Summary
5,6 & 7 week
By end of 9 weeks