![]() ![]() Formation of the neural tube -Forms from a special region of the ectoderm. Cite 5 early embryonic development stages 1-Cleavage: Morula.Ģ-Blastulation: form blastula with inner mass cells (form fetus) and trophoblast (form chorion and placenta).ģ-Gastrulation: formation of 3 germ layers.Ĥ-Neurulation development of NS-ectoderm. Determinate cleavage -Results in cells that are committed to differentiating into a specific cell type. Indeterminate cleavage -Results in cells that are capable of becoming any cell in organism. When does the zygote becomes an embryo? -After the first cleavage because its no longer unicellular. Early divisions of cells in the embryo, results in a larger number of smaller cells but the overall volume does not change. Cleavage -The division in animal cell cytoplasm caused by the pinching in of the cell membrane. The first 12-to 24-hours after a zygote is formed are spent in _ -Cleavage: very rapid cell division. Monochorionic/diamniotic twins? Monozygotic twins that each have their own amnion, but share the same chorion. Monochrionic/monoamniotic twins? Monozygotic twins that share the same amnion and chorion. Can be classified by the placenta structures they share (mono vs diamniotic, mono vs dichorionic). Identical monozygotic twins -Results from the splitting of a zygote in two. Fraternal dizygotic twins -Result from the fertilization of two eggs by two different sperm. When the first sperm penetrates, it causes release of calcium ions which prevents additional sperm from fertilizing the egg and increases metabolic rate of the resulting diploid zygote. Cortical reaction -A reaction that occurs during fertilization, when the sperm cell unites with the egg's plasma membrane, that prevents entry of a second sperm. Acrosomal Reaction and Sperm Penetration -Sperm binds to the zona pellucida andĪcrosomes release their enzymes to digest the zona pellucida. Acrosomal apparatus -Occurs once the first sperm comes into direct contact with the secondary oocyte's cell membrane and injects its pronucleus. ![]()
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