Egg of toad

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Egg of toad
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Cleavage
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Axis of cleavage
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Gastrulation

• Gastrulation carried out byMigration of cells
  from the surface Toward the blastopore (epiboly),
  followed By invagination and involution.
• The result is the formation of three germ layers
• Outre ectoderm.
• Middle mesoderm.
• Inner endoderm.

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Embryonic Development of Birds

• Fertilization Internal.
• Type of egg
• According amount of yolk Polylecithal type.
• According to distribution of yolk heavy
  telolecithal type.
• Kind of cleavage Discoidal cleavage.

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Female genital System
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• Cleavage
• 1st cleavage Vertical and give two blastomeres.
• 2nd cleavage At right angle to the first and
  give 4 blastomeres.
• 2rd cleavage Is radial at right angle to the
  second.
• 4th cleavage Central arround the apical end of
  the eight blastomeres.
• The cleavage proceeds with irregular manners with
  increased in the number of cells and spread over
  the surface of the yolk.

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• Formation of Blastula
• The blastomeres spread over the yolk surface
  with closely attachement to the yolk by both ends
  and the zone of attachement called zone of
  junction. The blastocoele is reduced and is
  called subgerminal space or segmentation cavity.
• Formation of Gastrula
• The blastoderm cells arranged in different
  cell layers. The innermost cell layers separated
  by a process called delamination forming outer
  epiblast and inner hypoblast which is known
  afterwords the ectoderm and endoderm.
• Or by different process of cell movements called
• Emboly convergence , invagination involution.
• Epiboly include overgrowth of the ectoderm and
  endoderm over the yolk mass.

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Embryonic Development of human

• Fertilization Internal.
• Type of eggs Alecithal type.
• Type of cleavage Equal holoblastic.
• Cleavage
• Ist occurs at right angles to imaginary axis
  and results in the formation of two blastomeres
  after 36-46 hours . The embryo still surrounds by
  zona pellucida to make close contact of the
  blastomeres.
• 2nd Occurs at prependicular axis at 60 hours
  and result in the formation of 4 blastomeres.
• 3rd Occurs at 70 hours and result in the
  formation of 8 blastomeres.
• At 72 hours The morula stage is formed and
  composed of 12 cell stage.The peripheral cells is
  called trophoblast and formed of 11 cells and the
  12th cell is very large and enclosed in the
  center and called inner cell mass.
• At 4 days 58 cell embryo is formed . The outer
  periphery trophoblast cells is formed of 53
  blastomeres. The inner cell mass composed of 5
  large cells.
• At 4.5-5 days 107 cell stage is formed with
  peripheral trophoblast cells composed of 99 cells
  and inner cell mass composed of 8 formative cells
  (inner cell mass).

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• Implantation
• At the 6th day , the zona pellucida become
  lysed after the blastula reached to the proper
  side of the endometrium . The trophoblast cells
  exert microvilli which intern exert a histolytic
  action on the endometrium epithelium facilitating
  penetration and implantation . By the end of 8
  days implantation is completed. After
  implantation the eendometrium is closed by fibrin
  clott. Implantation occurred at the posterior
  wall of the uterine tube near the fundus.
• Abnormal site of implantation (Ectopic
  pregnancy)
• Tubal pregnancy.
• Ovarian pregnancy.
• Abdominal pregnancy.

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• Gastrulation
• The inner cell mass divides into several cell
  layers. The outer is the ectoderm. The middle is
  mesoderm . The inner is the endoderm.
• Periods of pregnancy
• First trimester First 3 months.
• Second trimester Middle 3cmonths.
• Third trimester The last 3 months.

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Embryonic Membranes

• Found only in amniotic animals and formed mainly
  of 4 types
• A mnion.
• Chorion.
• Allantois.
• Yolk Sac.

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