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Embryology

Embryology. http://worms.zoology.wisc.edu/frogs/amphy.html. Stages of Development in Animals. Zygote Morula Blastula Gastrula Neurula. Processes. Fertilization Cleavage Gastrulation Organ formation. Fertilization.

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Embryology

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  1. Embryology http://worms.zoology.wisc.edu/frogs/amphy.html

  2. Stages of Development in Animals • Zygote • Morula • Blastula • Gastrula • Neurula

  3. Processes • Fertilization • Cleavage • Gastrulation • Organ formation

  4. Fertilization • Combines haploid chromosomes from two organisms to forms a single celled diploid zygote • Egg is surrounded by a thin cell layer called the follicle. • Follicle is loosened by an enzyme in the sperm

  5. Fertilization Continued • Next, sperm encounters Zona Pellucida where it bonds to glycoproteins  this is species specific • Membrane of acrosome (tip of sperm) fuses with membrane of egg • Changes the electrical potential of egg, preventing fertilization by multiple sperm • Activates the egg to begin development by stimulating the release of calcium

  6. Gray Crescent • At fertilization, an egg will shift dark pigment to the point of entry. • This exposes a “gray crescent” on the opposite side. • It turns out that during the first cell division, each new cell must get some of the gray crescent in order to develop into a normal adult.

  7. Cleavage • The cell divides, but there is no cytoplasmic growth (skips G1 and G2) • Polymerase and mRNA were stored in egg

  8. Cleavage • Repeated cell divisions create a morula (solid ball of 16 – 64 cells) from a single celled zygote. • Each individual cell is called a blastomere • These new cells pump sodium into the center of the cell mass creating a hollow blastula (the hollow center is blastocoel)

  9. Cleavage • Where there is little yolk, cleavage can proceed throughout the entire zygote unimpeded. (ex. Sea urchin) • Where much yolk is present, cleavage is impeded. Generally, the “yolkier” areas will divide more slowly and will result in larger cells.(ex. Frogs) • In such cases, the cells without yolk are “animal pole” and those with yolk are “vegetal pole”

  10. Cleavage

  11. Cleavage in reptiles, birds and fish • These animals have so much yolk that their cleavage is incomplete • Division occurs only in a small, caplike region

  12. Gastrulation and Neurulation • Rearranges the cells of the blastula • Formation of Germ Layers

  13. Amphibian Gastrulation

  14. Terms associated with Gastrulation • Gastrula • Blastopore • Archenteron • Germ layers-ectoderm, mesoderm, endoderm

  15. Ectoderm Mesoderm Endoderm skin notochord lining of gut brain muscles liningof lungs spinal cord blood lining of bladder all other neurons bone liver sense receptors sex organs pancreas Fate of Germ Layers http://www.ultranet.com/~jkimball/BiologyPages/F/FrogEmbryology.html

  16. Switch over to Campbell Activities on Gastrulation

  17. Neurulation • Neurulation involves the process of forming a neural tube. The tube is a forerunner of the central nervous system. • Ectoderm cells thicken into the neural plate. • The margins of the neural plate merge upward into a neural fold. • The neural folds meet and fuse to form a neural tube. The neural tube eventually differentiates into the brain and spinal cord.

  18. 24 Hour Chick Embryo

  19. 33 hour chick embryo

  20. 48 hour chick embryo

  21. Somites • Notice in the chick the presence of somites. • Somite cells contribute to the formation of the skin musculature, the body musculature, and the vertebrae.

  22. Human Development • The Visible Human Embryo

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