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4 Embryology, Growth and Development Sep14

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Krista Howarth

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Embryology ContinuedSeptember14131229 PMSlide 6Head of the sperm has structure called acrosome which as digestive enzyme that help digest through the membrane layerFlagella used to propell towards the cron radiata andOocyte plasma membraneThe once that reach near zona pellucidta Specific receptor ZP3 binding with spermThe sperm acrosomal cap binds to ZP3 and its called Acrosomal reactionActivation of digestive enzymes that break down the membrane of zona pellucidaActually takes quite a few secretion of many sperms to weaken the zona pellucida membrane enough to let one sperm throughFirst member that makes it through zona pellucida envounters plasma membrane of the oocyteThere is another receptor integrin a6B1 that immediately causes depolarizationChange of electric potential across plasma membrane that shocks away other sperms from attaching to plasma membraneThisis called Fast Block to PolyspermySlide 7Slow Block to PolyspermyPositive calcium ions released outside movement brings along water from the inside of the cellOocyte itself starts to shrink so there is space between zona pleuicida and plasma membraneThis allows zona pelucida to denatureStructural membrane change their structure and functionZP3 is a glycoprotein that changes nature and inactivatesThis leads to blocking of further attaching of spermsSlide 8Once the sperm has entered oocyte nucleus undergoes under second meiotic division and forms second polar bodyThe female nucleus is now called female pronucleusThe sperm head has detached from the tail and undergoes the process of become male pronucleusThese haploid nuclei fuse to form genetic materialAt this point the cell is referred to as zygote and ends fertilization stageSlide 9Series of cellular divisions the first division is the longest takes 1836 hoursAs the cells start to divide they are propelled back toward the uterus by cilia that are located in uterine tubeActual zygote moving back towards the uterine cavityAfter first cellular division zygote continues to divide as it moves toward the uterusAt this stage of zygote and first few cellular divisions the cell is referred to as totipotentIt means that it has capability of divide and differentiate to any cell of the bodySo morula is pluripotent or totipotentEventually when we get to the stage of 12 or more cells combined intoa solid cellular massThis structure is referred to MorulaCells turn from totipotent to pluripotent as cells divide away from Morula into blastocystNow they can become many types of tissues but not everyLittle bit differentiatedAs the cells divide the actual cell mass stay the sameThe cell gets smaller and smallerAt about 5 days Morula gets fluid filled cavity forming on the inside of the cell massThis cavity is referred to as blastoceleThe new structure that has this cavity inside is called a blastocystBy about day 6 it becomes hollow sphere type of structureOutside there is single layer of cell called trophoblast cellsSometimes the layer is referred to as feeding layer Trophoblast will become extraembryonic tissuesSuch as placenta amniotic tissues corionOrange in the picture is inner cell mass which eventually becomes embryo it is several layer thickDevelops into variety of germ layers and then further structures and tissues of the bodyOnce we get into blastocyst stage we come in contact with uterine wall and undergo process referred to as implantationInner mass cells tend to be directed toward the wall of uterus so they come in contact with the uterine wallDevelopment of twin could be going on here two waysDigyzotic twins are not identical also referred to as fraternal twins or sororal twinsTwo oocytes released each fertilized by different spermMonozygotic twins are identical twinsZygotes cell as they divide split awayThis way you have two zygotes that are identicalThey make their own two blastocysts individually embed into uterus wallIf happened early enough they will have their own placenta implantation siteDepending on when the zygote or morula or blastosyst divide to create these twins depend on the structure involved in developmentIf we see a split past day 8 typically you get conjoined twins they are attached at some sort of body structureDue to blastocyst already implanted in the wall and hard for cells to move away so they start growing into each otherSlide 10Uterine endometrium wall frontal section cut through by blastocyst in the diagramEmbryo is changing but the diagram is focused only on 812 days Kin 2Y03 Page 1
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