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Embryo lec 1

In the intrauterine we have 3 stages: 1. Pre-embryonic stage 2. Embryonicstage 3. Fetal stage

Pre-embryonic S : from fertilization till 2 weeks including implantation +zygote will travel from the fertilization area till implantation area through

the oviduct undergoing many divisions by mitosis and forming bilaminar

disk which will give us both ecto+ endo derm and mesoderm will form later

on

Embryonic stage : starts from 2-8 weeks called developing and formationstage where organs and tissues start to form (embryo)

Fetal stage : growing and increasing in size and weight no developing occurshere or formation from 8 weeks till birth

Embryo is more sensitive than the fetus coz of being at developing stage soit is more effected by environmental factors specially radiation and an

important note for us as a dentist is to never do any LA for any pregnant

lady in this period 2-8 weeks just do the minor things

Ovum + sperm will join to form the zygote which diploid cell and both ovumand sperm are haploid then as we said the zygote will travel through the

oviduct dividing giving smaller in size cells called blastomeres but keeping

the same diameter as unit

When zygote division reach to 12 or 16 cells it called morula and it is thesame size as the zygote 0.1-0.2 mm in diameter

After morula formation and through developing we will have a structurethat has a cyst in called the blastocoil and the whole structure will be called

balstocyst

Blastocyst will contain bilaminar disk which has 2 layers the 1 stis the onewhich will face the uterus wall called embryo epiplast and it has columnar

cells and will give us in the future the ectoderm 2nd

one is the one facing the

blastocoil called embryo hypoblast and it is flattened cells and will give us

the endoderm

Blastocyst structure will be divided into inner and outer surface the innerone will be the cell mass and the outer one will be zona pelli codia which is

very important for implantation and also here size is 0.1-0.2 mm in

diameter

After Blastocyst the structure will develop to have 2 cyst the blastocoil andthe amniotic cavity which will have the amniotic fluid

Structure will continue developing till we have more obvious amnioticcavity and primary yok sac + formation of the connecting stalk

At 3

rd

week there will be obvious structure developing

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Through 3rdweek formation of perochordal plate happens which is athickening of the endoderm overlying on the ectoderm leading to bulging in

the ectoderm this plate is located at cephalic pole eventually will give us

the buccopharengyal membrane separating the mouth (oral cavity) from

the guts ( GIT) also u can find similar duct on the caudal pole called theclocal membrane

Ectodermal dysplasia : X linked recessive disease effects males leading toloss of Ectodermal structure such as the skin appendages and the hair

follicle and enamel leading to 2 clinical condition first is due to loss of sweat

glands which hyperthermia scnd is the loss of enamel which may lead to

loss of teeth and cause oligodontia

Mesoderm layer will be formed from the ectoderm layer cell division thatwill invaginate at the middle under the ectoderm then go back to the same

way they come through then there will be formation of both premeditative

stalk and premetative nod

Mesoderm formation will be from caudal to cephalic pole direction Mesoderm layer will be formed after the 17 day of pregnancy The premetative stalk is important coz it will form the premetative nod the

will form the notochord that will give us an enclosed tube that will be

forming the vertebral column and the backbone and tube of spinal cord

Mesoderm can't be find always b/w ectoderm and endoderm coz it is onlyfound at perochordal plate structure but Git is formed by endo derm and

oral will be formed by ectoderm and there is no mesoderm in between

only at perochordal plate

Ectoderm will give: 1. Skin appendages 2. Enamel 3. Oral and anal mucosa4. Pituitary and mamillary gland 5. Nervous system 6. Eye lens 7. Lining of

nose and sinus

Endoderm will give: 1. Lingual tonsils 2. Lining of lungs 3. Digestive system4. Lining of excretory system

Mesoderm will give: 1. Lung /heart / blood cells 2. Excretory system 3. Alldental tissue except enamel 4. Spleen 5. Respiratory system 6. Connectivetissue 7. Bone / muscle 8. Lymphatic tissue

Forgive me for any mistake it is a summary for the first lec hope it is good for u and

only 1 thing am sure there will be a spelling mistakes forgive me for that it include

book and script and past year

Your colleague Ahmad fawzi