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Embryological Stages

Embryological Stages. March 23, 2011. Female Reproductive System. Fertilization: 0 hours. E gg is released from the ovary & moves into the fallopian tube to wait for the arrival of the sperm Fertilization - results in a zygote requires the sperm & egg nucleus to fuse

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Embryological Stages

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  1. Embryological Stages March 23, 2011

  2. Female Reproductive System

  3. Fertilization: 0 hours • Egg is released from the ovary & moves into the fallopian tube to wait for the arrival of the sperm • Fertilization- results in a zygote • requires the sperm & egg nucleus to fuse • Following fusion, egg plasma membrane undergoes changes that prevent entrance of other sperm • Then wave-like action of cilia move the fertilized egg toward the uterus for implantation to take place

  4. Fertilization of female egg

  5. Location

  6. Cleavage 2-cell: 24 hours • Cleavage: process by which a zygote divides by mitosis to form two new cells • mitosis and DNA replication occur repeatedly • Cell is no longer just one cell

  7. Location

  8. 4-Cell: 36 hours • Cleavage continues as two cells will divide to form 4 cells, and so on • Continue dividing until form a blastocyst

  9. Location

  10. 8-Cell: 48 hours 8-CELL STAGE IS KEY DIFFERENCE!!! • Either Protostomes or Deuterostomes depending on species • Protostomes (clams, worms, & insects) undergo spiral cleavage- cells divide and they do not sit on top of each other; they appear to spiral

  11. Deuterostomes • Deuterostomes- (starfish & vertebrates) cleavage results in 8 cells sitting directly on top of each other. This is called radial cleavage

  12. Location

  13. Morula 16-Cell: 60-84 hours • The eight cells now continue to divide until you are simply a large solid ball of cells (16-32 cells). Morula

  14. Location

  15. Blastula: 6 days • At this time, the morula begins to form a hollow ball of cells called the blastula. • The blastula contains a fluid filled space known as the blastocoel. BLASTOCOEL BLASTULA

  16. Location

  17. Gastrula: ~15 days • Blastula begins to fold inward on one side • When the folding occurs, it creates a horse shoe shaped structure that is 2 cell layers thick • Outer layer of the ball is called the ectoderm. • Inner layer of the ball is called the endoderm. • Eventually, another cell layer will begin to form between the endoderm and ectoderm. This layer is called the mesoderm. Mesoderm

  18. 3 Tissue Layers In Depth • Ectoderm- forms nervous system & outer layer of skin • Mesoderm- forms muscle, bone, & cardiovascular system • Endoderm- organs of digestive system, lining of respiratory system & bladder

  19. Gastrula (cont.) • The point where the horse shoe almost touches is called the blastopore (small hole) • In protostomes this will eventually form the mouth. • In deuterostomes this will form the anus Mesoderm

  20. Location

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