IMPLANTATION & GASTRULATION

STD-12      UNIT-6     CHA-3

HUMAN REPRODUCTION

IMPLANTATION &  GASTRULATION 

IMPLANTATION

• It means attachment of blastula to the endometrium of uterus for further development of embryo is called as implantation.
• Blastula remains free within the cavity of the uterus from 2 to 4 days before implantation.
• Ciliary movements of fallopian tube and muscular movements of fallopian tube, blastula runs towards uterus after blastulation . 
• Blastocyst gets attached to the endometrium of uterus on 7th or 8th days of fertilization in post ovulatory phase.
• During this time nourishment is provided by secretions of endometrium called as uterine milk.

•  As the blastocyst gets implanted the trophoplast separates into two layers in the region of contact between blastocyst and endometrium . 
• These layers are outer syncytiotrophoblast and inner is cytotrophoblast,  
• During implantation the syncytiotrophoblast secretes enzyme that enable the blastocyst to penetrate the uterine lining .  
• This enzyme digest and liquefy the endometrial cells . 
• The fluid and nutrients further nourish the burrowing blastocyst for about a week after implantation . 

• Then blastocyst become buried in the endometrium usually on the posterior wall of fundic uterus or body of uterus.
• Implantation provides support to embryo protection of embryo,  development of embryo and nourishment of embryo during pregnancy .

GASTRULATION

• Rearrangement of the cells of embryoblast in blastula to form three germ layers ectoderm endoderm and mesoderm is called as gastrulation . 
• It is characterized by morphogenic movement of cells of embryoblast of blastula.

• The cells of embryoblast in blastula get separated due to presence of uterine fluid in blastocoel cavity . 
• During formation of endoderm some cells covering the free surface of embryonal knob become flat and form first endodermal cells . 
• These endodermal cells rapidly multiply spread out in all directions and soon form a complete lining inside trophoblast of the blastodermic vesicle,the endoderm is located under embryonal knob is embryonic endoderm.
• The endodermal tube so formed is primitive gut or archenteron , it cavity is called gastrocoel cavity.
• During formation of embryonic disc to blastocyst continuous to grow in size . 
• After formation of endoderm, the embryonic knob become columnar embryonic disc . 
• The space between embryonic knob and trophoblast cells is called as amniotic cavity, 
• Amniotic cavity is filled with amniotic fluid.

• After the formation of endoderm remaining cells move toward trophoblast of animal pole and get arranged in one layer below the trophoblast called as embryonic ectoderm.
• The cells present at posterior end of the embryonic disc get proliferated at high rate.
• Due to addition of cells thickness of the embryonic disc increase.
• These proliferated cells latter detach from embryonic cells and spread between the trophoblast and endoderm.
• The new layer of cells scattered in the blastocoel cavity and arranged in one layer called embryonic mesoderm.
• A large cavity present in the gastrula formed in extra embryonic membrane mesoderm is called as extra embryonic coelom.
• Outer mesoderm lining of trophoblast is called as parietal extra embryonic mesoderm.
• Inner mesoderm covering primary yolk sac and wall of the amniotic cavity is termed as visceral extra embryonic mesoderm .

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