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Development of Animal Cells Aka…Embryology Embryology - study of the development of an embryo 5 major stages… 1. Gametogenesis - gamete production 2. Fertilization - gamete --> zygote 3. Cleavage - Zygote --> Blastula 4. Gastrulation - Blastula --> Gastrula 5. Organogenesis - Organ Formation -i.e. Neurulation- Gastrula --> Neurula Fertilization: male and female gametes fuse to form a zygote Funnel shaped end of a Fallopian Tube is the usual site for fertilization A sperm must penetrate the egg Now it is called a ZYGOTE Tiny cilia line the tube to propel the fertilized egg toward the uterus Cleavage (Process by which a zygote divides by mitosis to form 2 new cells) Cell # doubles with each division (two cells will divide to form ___ cells and so on) each cell smaller than zygote MORULA: a zygote consisting of about 12-32 cells in a solid ball Reaches the uterus in about 3-4 days after fertilization BLASTOCYST formation Cells start to compact and move to the edge of the cell, leaving a fluid-filled space in the center- this will eventually form the Blastocyst (also called blastula for other animals) a. b. c. a hollow ball of cells that forms btwn 5-8 days after fertilization This will attach to the lining of the uterus cell division continues Cells on 1 side of the blastocyst begin to fold inward to form the gastrula Blastocyst structure Three parts: Blastocoel- fluid filled empty space Inner Cell Mass- embryonic stem cells No longer OMNIPOTENT cells. Now they are PLURIPOTENT (can become anything except the placenta) Trophectoderm- outer layer of cells Provides nutrients to the developing embryo and will eventually form the placenta Gastrulation Blastula (hollow ball of cells) transformed into the Gastrula (three-layered stage) Gastrulation - sorts all the cells into distinct cell layers (ectoderm, endoderm, and mesoderm) Gastrulation forms 3 distinct tissue layers Layer on the outer surface of the gastrula is called the ECTODERM eventually forms the SKIN and NERVOUS tissue ENDODERM Layer on the INNER SURFACE of the gastrula is called the ENDODERM ENDODERM eventually develops into the lining of the digestive tract and organs associated with digestion MESODERM Mesoderm is the 3rd cell layer found in the developing embryo between the ECTO and ENDODERM (“meso” means middle) MESODERM Continues to grow and divide and eventually develops into muscle cells, circulatory, and excretory cells, bone cells and respiratory system