Embrology PowerPoint by Prof Hanaa Aly Presentation

7/31/2019 Embrology PowerPoint by Prof Hanaa Aly Presentation

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EmbryologyPRESENTED BYPRESENTED BY

HANAA ALY

PROFESSOR OF ORAL BIOLOGYPROFESSOR OF ORAL BIOLOGY

ALEXANDRIA UNIVERSITYALEXANDRIA UNIVERSITYProf. Hanaa Aly


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It is the study of growth and differentiationwhich an organism undergoes during its

life from a sin le cell to a com lex

independent living being.

Development of individual is divided into :

A)Prenatal Development B) Postnatal Development

Prof. Hanaa Aly


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A- Prenatal DevelopmentIt can divided into 3 periods:

The proliferation period

The embryonic periodThe fetal period

B- Postnatal Develo ment

It is divided into six periods :

i) Neonatal period

ii)Infancy

iii) Childhood

iv) Puberty

v) Adolescence

vi) Early adulthood Prof. Hanaa Aly


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First week: In the 1st week fertilization takes

place, the morula forms and is converted into a

blastocyst

Prof. Hanaa Aly


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The blastocyst consists of embryoblast,

and the trophoplast function?

Prof. Hanaa Aly


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Abnormality in number of chromosomes iseither increase or decrease in number

decrease in one chromosome is called

monosomy which is usually lethal .

Increase in number is called teratogenic

and an example for trisomy is Downsyndrome ,Mongolism

Prof. Hanaa Aly


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Genetic Abnormalities

Examples of Autosomal Dominant Genes are

1)Achondroplasia

2)cleidocranial dysostosis

3) Mandibulofacial dysostosis

4)Dentinogenesis imperfecta

Prof. Hanaa Aly


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Second week:

morphologic changes occur in the inner cell mass.It differentiates into a plate

called the bilaminar embryonic disk or germ

formed of two layers:An endoderm layer consisting of cuboidal cells facing the blastocele

and an ectoderm layer of columnar cells

adjacent to the endoderm and facing the trophoblast

Prof. Hanaa Aly


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prochordal platethickened area ofendoderm

oropharyngeal membrane The prochordal plate fuseswith the overlying embryonic ectoderm

Two embryonic cavities are

The u er cavit or the amniotic cavit soon

becomes lined with amnioblast derived fromthe ectodermal layer which forms its floor.

The lower cavity or (the secondary yolk sac)becomes lined with endoderm developed from

the migration of cells at the periphery ofendodermal layer which forms its roof

Prof. Hanaa Aly


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Third week: IntraembryonicMesoderm Formation:

groove appears in the midline of the surface

of the ectoderm caudally, theprimitive groove.The end of this groove cranially deepens to formtheprimitive pitand the elevated margin around the pit iscalled theprimitive node.

The entire structure is called theprimitive streak

Prof. Hanaa Aly


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Cells from the primitive streak migrate between the ectoderm and

endoderm layers to form intraembryonic mesoderm. The mesodermal cells migrate anteriorly on each side of the

midline until they meet at the cephalic end of the embryonic diskin front of the prochordal plate.

m gra e a era y un ey ecome con nuous w e

extraembryonic mesoderm The mesoderm, therefore, exists between the ectoderm and the

endoderm everywhere Expect

at the prochordal plate (the oropharyngeal membrane) craniallyand at caudally, the cloacal membrane (tail end).

Prof. Hanaa Aly


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Induction ?The first inductive event occurs on day 18

neural plate: a thickening of

ectoderm dorsal to thenotochord. It is oval in shapewhen viewed from theectodermal surface.

neural fold neural tube

anterior or rostral neuropore

posterior neuropore. These

pores close during the 4thweek to establish the centralnervous system (brain andspinal cord)

Prof. Hanaa Aly


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neural crest cells

multipotent ectomesenchyme

mesenchyme produced from ectoderm which formsp nen v n e . e e e e en

ganglia and the sympathetic neurons, meninges, Schwanncells and pigment cells, most of the mesenchyme of thebranchial arches, face and teeth.

if they fail to migrate they result in a syndrome calledmandibulofacial dysostosis which is a congenital

malformation ?

Prof. Hanaa Aly


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Fate of the Three Germ Layers

ectoderm will give rise to the nervous system and the sensory epithelium of the eye, ear, and nose, the

epidermis of the skin and its appendages (hair, nails and glands), the surfaceepithelium lining the oral cavity, the nasal cavities and the sinuses, the parotidsalivary glands and the anterior lobe of the pituitary gland, the surface epithelium

endoderm gives rise to the surface epithelium lining the gastrointestinal tract and all associated glands,

including the submandibular and sublingual salivary glands, the surfaceepithelium lining the pharyngeal mucosa, the soft palate and the posterior 1/3 ofthe tongue.

mesoderm gives rise to

the muscles including the muscles of the tongue, all the structures derived fromconnective tissue e.g., dermis of the skin, lamina propria of the oral mucosa, bone,cartilage, blood, dentin, pulp, cement and periodontal ligament.

Prof. Hanaa Aly


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Suggested Reading

Avery, J. K. (1997) OralDevelopment and Histology, 3rd edition St Louis: Mosby Company.

Bhaskar, S. N. (ed) (1991) Orban's Oral Histology and Embryology , 11th

Edition St, Louis; Mosby Year Book, Inc

Lersen, W. J. (1998)Essential of Human EmbryologyEdinburgh: Churchill Livingstone.

Prof. Hanaa Aly

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Embrology PowerPoint by Prof Hanaa Aly Presentation