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Understanding Animal Development: Cleavage to Organogenesis in AP Biology

Explore the intricate process of animal development, from rapid cleavage to the formation of major organs and organ systems through gastrulation and organogenesis. Learn about germ layers, placental mammals, neurulation, and amniotes in this comprehensive AP Biology lecture.

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Understanding Animal Development: Cleavage to Organogenesis in AP Biology

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  1. Ch 33 animal development AP Biology Lecture

  2. Cleavage • Rapid series of cell division. Embryo becomes a ball of even smaller cells • Blastocoel- fluid filled cavity that forms • Cell now referred to as a blastula. • Individual cells called blastomeres.

  3. Complete Cleavage • Little yolk (stored nutrients) • All blastomeres equal size

  4. Incomplete Cleavage • Lot of yolk • Embryo forms as a disc of cells, blastodisc, on top of the yolk mass

  5. Mammal Cleavage • During 4th division, cells separate into two groups • Inner cell mass • Becomes embryo • Pluripotent • Surrounding outer cell • Trophoblast, an encompassing sac • Secretes the fluid to make the blastocoel • Becomes support structure to attach embryo to uterine wall

  6. Gastrulation • Blastula altered into embryo with multiple tissue layers and distinct body axes *body plan and first organs* • The germ layers form • Endoderm – innermost, from blastomeres inside the embryo Produces lining of digestive and respiratory tract

  7. Ectoderm – outermost, from cells outside the embryo • Produces nervous system and epidermal layer of skin • Mesoderm – middle layer, cells in between endoderm and ectoderm • Produces heart, blood vessels, muscles and bones

  8. http://bcs.whfreeman.com/thelifewire/content/chp20/2002001.htmlhttp://bcs.whfreeman.com/thelifewire/content/chp20/2002001.html

  9. Placental mammals • Inner cell mass splits • Upper layer- epiblast • Cells from endoderm and mesoderm • Eventually embryo • Lower layer- hypoblast • Eventually placenta

  10. Organogenesis • Development to form major organs and organ systems • Neurulation – formation of the nervous system • Neural plate- groove between folds eventually forms a hollow cylinder, neural tube, an overlaying layer of epidermal ectoderm • Some cells do not form into the neural plate but form neural crest which becomes the connection between the brain/spinal cord and rest of the body

  11. Segmentation during neurulation called somites • Found around the notochord • Produce cells that become • Vertebrae • Ribs • Muscle of trunk • Muscle of limbs • Lower layer of skin

  12. Amniotes • Extraembryonic membrane around the embryo • Nutrition • Gas exchange • Waste removal

  13. Mammals entire trophoblast embeds into the uterine wall • Hypoblast form chorion, membrane that limits water loss and aids in gas exchange • Chorion and maternal tissue form the placenta • Epiblast produces amnion, fluid filled amniotic cavity around the embryo

  14. http://lcmrschooldistrict.com/roth/PowerPoint_Lectures/chapter42/videos_animations/cleavage_implant.htmlhttp://lcmrschooldistrict.com/roth/PowerPoint_Lectures/chapter42/videos_animations/cleavage_implant.html

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