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Lecture 13

BIOSC 0160 Lecture 13: Biology 2 Lecture 2.3: Gastrulation and Organogenesis

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Biological Sciences
BIOSC 0160

Biology Week 8 Lecture 2.3 How do animals develop? (Gastrulation and organogenesis Fertilization Cleavage o Blastulation: solid ball of cells produced via cleavage forms a blastula with a fluidfilled cavity called the blastocoel Prevents cells from interacting too early Allows room for cell movements during gastrulation Gastrulation o Process by which a blastula is transformed by massive movements of cells into a gastrula An embryo with three germ layers and distinct body axes o Three germ layers Endoderm: innermost layer created by cells that move inward; gives rise to the epithelial lining of the digestive tract, respiratory tract, pancreas, thyroid, and liver Ectoderm: outermost layer will give rise to the nervous system, cornea of the eye, epidermis of the skin, epithelial lining of the mouth and rectum Mesoderm: middle layer, cells that move between endoderm and ectoderm; gives rise to reproductive organs, blood vessels, dermis of skin, muscle and bone o Different types of cell movements Invagination: inward movement of a cell layer forming a cavity Invagination at the vegetal pole initiates gastrulation, forms the archenteron (primitive gut, the part that infolds) and endoderm in sea urchin Mesenchyme cells break free and migrate into cavity, they will give rise to the mesoderm Involution movement of a sheet of cells under another layer of cells Ingression: breaking off and migrating of individual cells Epiboly: Thinning and moving of a sheet of cells over another layer o Fate maps: blastomeres can be dyed and followed through gastrulation to determine which blastomeres form the different germ layers Blastopore: major organizational center, site where major cell movement will begin Opening of the archenteron, forms the anus in the deuterostomes and the mouth in protostomes o Initiated in amphibians when cells in gray crescent change shape and move inward creating a slit called the dorsal lip The dorsal lip indicates which side will be the dorsal side Additional surface cells migrate inwards over the lip forming a sheet of cells under the outer cell layer (involution)
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