anim_fertilization_development_answer_key.doc

Fertilization and Development To complete this worksheet, select: Module: Continuity Activity: Animations Title: Fertilization and Development Fertilization 1. Define fertilization. Process by which two gametes from the parents fuse their genetic information to form a new zygote. 2. Where does fertilization occur? In the oviducts. 3. a. Describe sperm movement relative to the corona radiata and the zona pellucida. Once sperm penetrate the secondary oocyte’s corona radiata they enter the area of the zona pellucida. A glycoprotein in the zona pellucida binds to sperm and triggers the release of digesting enzymes. b. What role do digestive enzymes have in this process? These enzymes help to digest a path for the sperm to reach the plasma membrane of the secondary oocyte. c. Define syngamy. This is the first sperm to penetrate the entire zona pellucida and fuse with the secondary oocyte. d. How is polyspermy prevented? When fusion of the sperm and secondary oocyte occur there are changes in the membrane of the secondary oocyte that prevent polyspermy. 4. a. When is meiosis II completed? After the sperm penetrates the secondary oocyte. b. What is the purpose of the polar body? These are vestigial; they fragment and degenerate. Embryonic Development 5. Define the embryonic period. The 1st through 8th week of development. 6. a. Define each of the following: cleavage – mitotic cell division resulting in blastomeres. blastomeres - these are the individual cells that result from cleavage. morula – this is a solid ball of blastomeres formed on or about the 4th day. blastocyst – This is formed on the 5th day; the embryo sheds the zona pellucida and becomes a hollow ball of cells. b. How long does it take for the morula to reach the uterus? 5 – 6 days. 7. Contrast the inner cell mass and the trophoblast cells. The cells making up the perimeter of the blastocyst are the trophoblast cells and they will contribute to the formation of the placenta. The collection of cells on one end of the blastocyst called the inner cell mass will form the embryo. 8. When does the blastocyst implant into the endometrium? By day 6. 9. Identify and/or describe the function of the following Day 8 developments: cytotrophoblast layer – this is the innermost cell layer of the blastocyst. The cells are separated from each other. syncytiotrophoblast layer – This is the outer layer of the blastocyst that secretes enzymes to further promote implantation, as well as human chorionic gonadotropin, a hormone that acts to maintain the endometrium. The cells are connected into a single cytoplasmic mass with multiple nuclei. 10. Describe formation of the bilaminar embryonic disc. Identify the hypoblast and epiblast layers. The bilaminar embryonic disc is comprised of the hypoblast layer and the epiblast layer both differentiated from the inner cell mass. 11. a. Identify and describe the fluid filled amniotic cavity. During the 9th day the epiblast cells begin to multiply and cells on the surface of the epiblast delaminate to form the fluid filled amniotic cavity. b. Identify the yolk sac. Note the bilaminar embryonic disc location immediately between the yolk sac and the amniotic cavity. During the 9th day the multiplying trophoblast cells begin to develop into a yolk sac. 12. a. Describe chorion formation from the extraembryonic mesoderm. On the 12h day, differentiation of the yolk sac cells forms an extraembryonic mesoderm. This new layer, along with the syncytiotrophoblast and cytotrophoblast, forms the chorion. b. Describe the importance of the chorion. The chorion grows to form a connecting stalk which will later become the umbilicus. The chorion forms the embryonic portion of the placenta. 13. a.What is the importance of the three germ layers formed during the third week? The germ layers provide cells for organ formation in the following months. All tissues of the body arise from these 3 germ layers. b. What is the importance of the primitive streak? This forms on the surface of the embryonic disc. With its formation one is able to recognize the head and tail ends of the embryo. 14. Describe formation of: endoderm germ layer – derived from some of the epiblast cells that migrate together and differentiate and replace the hypoblast. mesoderm germ layer – Derived from epiblast cells that migrate and differentiate to form a layer between the epiblast and the hypoblast. ectoderm germ layer – Whatever cells have not differentiated into the mesodermal or endodermal layers differentiate into the ectoderm. 15. Describe the developmental importance of each part of the trilaminar embryonic disc: ectoderm – The ectoderm gives rise to all nervous tissue and the epithelium of the skin. mesoderm – The mesoderm gives rise to blood, muscle, bone and connective tissue. endoderm – The endoderm forms into the epithelium of the gastrointestinal tract, the respiratory system and other organs, 16. Describe the origin and importance of the notochord. Originates as a differentiation of mesodermal cells. The notochord is important in starting or inducing the specialization of other cells, including those directly above called the neural plate. 17. Describe the developmental importance of the neural fold, which ultimately becomes the neural tube, and the somites. Epiblastic cells on the neural plate are induced to begin to mound up and fold into a groove that continues to fold. The adjacent notochord mesodermal cells are induced to form somites, the eventual other source of cells to form skeletal and connective tissues, as well as muscle tissue. The neural tube arises and its cells eventually develop to form the brain, spinal cord and other parts of the nervous system. 18. a. Describe primitive blood vessel and heart formation. Mesodermal cells from the primitive streak rearrange to form blood vessels in and a primitive heart. b. Describe the function of the intervillous space. In the placenta, the endometrium forms maternal blood filled cavities called the intervillous space which baths the fingerlike projections of the chorionic villi.This arrangement allows for exchange of nutrients and materials between the maternal and fetal circulations without physical mixing of fetal and maternal blood. 19. Describe organ development during the fourth week. The embryo is formed and organogenesis begins. The nervous system and chorion continue to develop. The heart and the rest of the cardiovascular system continue to form. The digestive system begins to form and portions of the entire digestive tract are present. Ear, eyes and limb buds develop. 20. Describe development during the second month. There is rapid development of the head and limbs as well as continued organogenesis. The growth of the brain and head is rapid., hands and feet form, upper and lower limbs develop and individual digestive organs form. By the end the 8th week limbs are complete, digits are separate, eyes are open and external genitalia appears. Blood cells also appear. At the end of the second month of development the embryo is now referred to as a fetus. Fetal Development 21. Describe development and activity during weeks 9-12. A large head is formed. There are visible eyes and ears and a detectable heartbeat. The kidneys form urine, gender identification is possible and there are weak body movements. The placenta is also exchanging nutrients and producing essential hormones. 22. Describe development and activity during the fourth month (Weeks 13-16). A human look becomes apparent and eyes and ears move to their final positions. Organogenesis development occurs more rapidly and the gender is easily determined. The fetus weighs about 4 ounces and is 6 – 7 inches long. 23. a. Describe development and activity during the fifth month. The fetus now weighs about one pound, movements are very perceptible. Organogenesis continues and fine hair called lanugo forms all over the fetus. b. What is lanugo? Fine hair. 24. Describe development and activity during the sixth month. The fetus is about 14 inches long and starts making some surfactant in the fetal lungs and it begins to practice breathing movements. The eyes are almost completely developed and the fetus can respond to noise outside the uterus. 25. Describe development and activity during the seventh month. The fetus increases to 2-3 pounds and it gains body fat. The testes descend into the scrotum. 27. Describe the development and activity during the eighth month. The fetus continues to accumulate subcutaneous fats and reaches a weight of about 5 pounds. The fetus also assumes an upside down position in preparation for birth. Sucking, sleeping and waking are also on the agenda. 28. Describe the development and activity during the ninth month. Most of the lanugo is shed and the brain continues to develop. The fetus weighs about 7 pounds, is about 20 inches long, and has also accumulated about a quart of amniotic fluid that surrounds and protects the fetus. The fetus is ready to leave the womb and begin life on its own.