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Vertebrate Development

Vertebrate Development. Biology II: Form and Function. The six stages of vertebrate development. Fertilization Cleavage Gastrulation Neurulation Neural crest formation Organogenesis. Stage of vertebrate development (I). Stage of vertebrate development (II). Fertilization (I).

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Vertebrate Development

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  1. Vertebrate Development Biology II: Form and Function

  2. The six stages of vertebrate development • Fertilization • Cleavage • Gastrulation • Neurulation • Neural crest formation • Organogenesis

  3. Stage of vertebrate development (I)

  4. Stage of vertebrate development (II)

  5. Fertilization (I) • Entry of sperm cell induces activation • prevents other sperm from entering • Intitiates second meiotic division of egg nucleus • Induces polarity

  6. Fertilization (II)

  7. Fertilization in sea urchins

  8. Sperm penetration

  9. Polarity in early embryos

  10. Cleavage • Division of first cell to many within ball of same volume (morula) is followed by hollowing of that ball to a blastula. Form of cleavage and blastulation depends on orientation of yolk and nucleus • In primitive chordates, division is even, towards a symmetrical blastula composed of cells of equal size • In amphibians, holoblastic cleavage leads to assymetrical blastula • In reptiles and birds, meroblastic cleavage occurs, resulting in a cap of cells on top of the yolk • In mammals, holoblastic cleavage occurs, creating a trophoblast containing a blastocoel, with inner disc of cells equivalent to a blastodisc

  11. Yolk distribution in amniotic eggs affects blastula development

  12. Holoblastic cleavage • Cells with little yolk, and central nucleus, develop evenly

  13. Uneven cleavage • In frog cells, there is more yolk, and nucleus of fertilized egg is to one side: • Yolk slows division, so areas of low yolk content divide quicker, and create smaller cells (see here, front) • Areas of high yolk content divide more slowly, and give rise to larger cells

  14. Meroblastic cleavage • Occurring in reptiles, birds and mammals, an uneven division of cells causes a cap of cells on top of the yolk

  15. Blastula of mammals and birds • Cap of cells develops into a blastodisc • Blastocoel develops in mammals, surrounded by trophoblast

  16. Gastrulation • Invagination of outer layer of cells to inside of the blastula is known as gastrulation, resulting in the formation of the gastrula • Type of gastrulation is a function of type of blastula… • End result is three types of germ layer tissue - endoderm, mesoderm and ectoderm

  17. Gastrulation in the lancelet

  18. Gastrulation in the frog

  19. Gastrulation in birds

  20. Gastrulation in mammals

  21. Neurulation and neural crest formation • Formation of neural fold (primitive streak) above notocord, begins a channel that eventually seals on the dorsal surface, forming neural groove • Mesoderm derived tissue close to notocord develop into somites, giving rise to muscles, connective tissue and vertebrae • Layer of cells on dorsal surface of groove form neural crest, responsible for formation of several important organs • Associated patches of ectoderm tissue derive into placodes, which evetually result in important neurally related organs

  22. Neural tube formation (I)

  23. Neural tube formation (II)

  24. Induction • Proximity of a cell to certain other cells controls its development - Spemann and Mangold • Cells whose fate can be predicted are termed ‘determined’ • Cells whose fate cannot be reversed are termed ‘committed’ • Since all cells initially can become any tissue... ...Development is a process of progressive restriction of gene expression

  25. Spemann and Mangold’s dorsal lip transplant experiment

  26. Induction of the vertebrate eye

  27. Organogenesis • Ontogeny recapitulates phylogeny • (and a quick word about extraembryonic membranes)

  28. Derivation of major tissue types

  29. Embryonic development of vertebrates (I)

  30. Embryonic development of vertebrates (II)

  31. Extraembryonic membranes - Chick embryo

  32. Extraembryonic membranes - mammalian embryo (I)

  33. Extraembryonic membranes - mammalian embryo (II)

  34. The placenta

  35. Human development

  36. Developing human at 4 weeks

  37. Developing human at 7 weeks

  38. Developing human at 3 months

  39. Developing human at 4 months

  40. Ultrasound at 5 months

  41. Delivery position of foetus

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