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Chapter 42 Review: Embryology and Stem Cells 1. What are the three processes that allow a zygote to transform itself into an embryo? Cell division(cleavage), cell migration and cell differentiation 2. Place the following stages of development in order: gastrula, organogenesis, zygote, blastula, morula, blastopore formation Zygote, morula, blastula, blastopore formation, gastrula, organogenesis 3. Which organ/organ systems would fail to develop if the endoderm did not form? Lining of digestive and respiratory systems 4. Which organ/organ systems would fail to develop if the ectoderm did not form? Skin and nervous system 5. Which organ/organ systems would fail to develop if the mesoderm did not form? Skeletal, circulatory, and muscular systems 6. What type of cell division are cleavage divisions? mitotic 7. What happens to cell size as cleavage divisions occur? Decreases (no growth between divisions) 8. What happens to the embryo size as cleavage divisions occur? Remains unchanged (cells get smaller) 9. How is the cleavage division cycle different from the typical mitotic cell cycle?growth portion of interphase is skipped 10. How does a morula become a blastula? Cells inside the morula migrate outward to hollow out the center 11. How does a blastula become a gastrula? Cells on one side of the blastula migrate into an area called the blastopore creating an inner tissue layer called endoderm. Later cells migrate between the outer and inner layers creating mesoderm (middle layer). 12. In what way are all the cells in your body similar? What makes them different? They all have the same DNA. Different genes are expressed 13. Describe the two mechanisms that direct the developmental fate of embryonic cells? (Tell the cells where to go and what to become.) Induction: chemical messages released from cells activate genes in neighboring cells instructing them to migrate or differentiate. Gene Regulatory Substances originally in the egg cytoplasm are distributed to daughter cells during cleavage divisions. These active or silence genes causing the cells to migrate and differentiate. 14. Where do gene regulatory substances come from? How do they get distributed into the cells of the embryo? The egg cytoplasm. Cleavage divisions 15. Identify the correct stage of development for each of the starfish embryos in the table below: Embryo Stage of Development Embryo Stage of Development 4 cell stage Morula (solid ball of cells) Gastrula (early to mid) Dark streak is the cells migrating into the blastocoel. The inside of the streak will become the digestive tract. The cells lining the streak become the endoderm. The outer layer of cells around the entire gastrula is the ectoderm. Eight cell stage (not all cells visible) Blastula (hollow ball of cells) Lighter center is the blastocoel; the hollow chamber inside Late Gastrula Ectoderm Mesoderm Endoderm Late Blastula to early gastrula The flat area on top is the beginning of the blastopore. Two cell stage Stem Cell Review: 1. List the three types of stem cells you learned about. Somatic (adult), Induced Pluripotent, Embryonic 2. How are embryonic stem cells obtained? Removed from the inner cell mass during the blastocyst stage (57 days after fertilization) 3. How are induced pluripotent stem cells created? A specialized cell from the patient is removed and exposed to chemicals that cause it to dedifferentiate. These cells can then be programmed to develop into any needed cell type. 4. What do adult (somatic) stem cells do in an organism?allow for growth, tissue repair and maintenance throughout the life of the organism 5. Complete the following table for the three types of stem cells Feature Embryonic Stem Cell Induced Pluripotent Stem Cell Potential to become any X X cell type Potential to become only a limited range of cell types Ethical issues due to X destruction of an embryo to obtain Therapeutic use could X cause immune rejection by the patient Found in bone marrow Adult (somatic) stem cell X X Solid Ball of Cells Hollow ball of cells Fertilized egg Morula Mitotic cell division with little or growth inbetween Blastula Cell with the potential to become any cell type in the body Zygote Indentation in the blastula through which cells migrate during the beginning stage of gastrulation Cleavage Stem Cell Cavity inside the blastula Blastocoel Blastopore Process by which Embryo with three cells release chemical tissue layers messages that determine the Gastrula developmental fate of neighboring cells Induction Process by which cell The term for a human Process by which migration transforms blastula cells take on a blastula into a specialized structures gastrula and functions blastocyst gastrulation differentiation Genes that direct the Stem cells obtained development of from a blastocyst entire body segments; arranged Embryonic stem cells Stem cells responsible for growth, repair and maintence of tissues “head to toe” on the chromosome throughout the life of an organism homeobox Tissue layer that gives Tissue layer that gives rise to the lining of rise to the skin and the digestive and nervous system respiratory tracts ectoderm endoderm Somatic stem cells Tissue layer that gives rise to the circulatory, skeletal and muscular systems. mesoderm Stem Cells produced by reprogramming specialized cells to dedifferentiate The development of organs and organ systems from the three tissue layers Induced Pluripotent organogenesis