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WEEK 3:
Embryology 2
| Question | Answer |
|---|---|
| when does blastocyst attach to endometrium | 7 days after fertilisation |
| implantation site | posterior endometrium wall of uterus (nearer fundus than cervix) - in the functional layer of endometrium |
| what happens when the blastocyst first implants | disappearance of zona pellucida |
| cells in trophoblast of blastocyst | 55 |
| cells in inner cell mass of blastocyst | 5 |
| what can the inner cell mass be split up into | primitive ectoderm (epiblast) + primitive endoderm (hypoblast)- which surorund cavity of yolk sac |
| ectoderm aka | epiblast |
| endoderm aka | hypoblast |
| ectoderm (epiblast) surrounds what | amniotic cavity (top) |
| endoderm (hypoblast) surrounds what | yolk sac cavity (bottom) |
| 2 layers of blastocyst wall (trophoblast) | cytotrophoblast + syncytiotrophoblast |
| together the epiblast and hypoblast make what | bilaminar disc |
| exocoelomic membrane | thin cell layer lining inside of cytotrophoblast |
| exocoelomic cavity vs yolk sac | yolk sac = + exocoelomic cavity = space inside yolk sac |
| by day 10 what happens | blastocyst completely embedded into endometrium + epithelial continuity restored (formed back) |
| extraembryonic mesoderm consists of what | consists of loosely arranged cells filling space between exocoelomic membrane + cytotrophoblast, developed from trophoblast + hypoblast |
| role of lacunae in syncytiotrophoblast | network to establish early uteroplacental circulation |
| extraembryonic coelom | fluid filled cavity in extraembryonic mesoderm separating it into extraembryonic somatic mesoderm + extraembryonic visceral mesoderm |
| endometrium decidual reaction | endometrial cells become glycogen/ lipid cells + swell more to support developing embryo |
| cytotrophoblast | inner trophoblast layer producing primary chorionic villi |
| syncytiotrophoblast | outer trophoblast layer |
| (somatic) extraembryonic mesoderm | surrounding epiblast layer of amniotic cavity |
| (visceral) extraembryonic mesoderm | surrounding hypoblast layer of yolk sac |
| connecting stalk | made of extraembryonic mesoderm attaching to trophoblast |
| outcomes at end of 2nd gestational week | 2 layers (ectoderm + endoderm = bilaminar disc), 2 cavities (amniotic + yolk sac), 2 trophoblast layers (cytotrophoblast + syncytiotrophoblast) |
| problems with implantation | hydatidiform mole, abnormal implantation (ectopic pregnancy), twins malformation |
| hydatidiform mole description | only trophoblast layers proliferate + secrete hCG, no embryo develops + appears pregnant but ultrasound (prenatal diagnosis) shows no embryo |
| cause of hydatidiform mole | sperm fertilise egg with no female pronucleus |
| risk of 2nd molar pregnancy after 1st | 1% |
| chance of ectopic pregnancy (uterine tube) | 94% |
| cause of abnormal implantation | uterine epithelium damaged (scarring, pelvic inflammatory disease) or zona pellucida lost too early causing premature tubal implantation |
| when and how many twins divide | 99% within 8 days of fertilisation |
| when do dichorionic- diamniotic twins form (DiDi) | 1-3 days |
| when do monochorionic + diamniotic twins form | 4-8 days |
| when do monochorionic + monoamniotic twins form | 8-13 days |
| when do conjoined twins form | 13-15 days |
| dichorionic meaning | two chorions |
| diamniotic meaning | two amniotic cavities |
| monochorionic meaning | one chorion |
| monoamniotic meaning | one amniotic cavity |
| dichorionic-diamniotic twins | split by day 3, resulting in mostly DZ twins + 25% MZ twins with the lowest mortality risk of 9% |
| type of cell at days 1-3 | morula |
| monochorionic-diamniotic twins | same placenta + 2 amniotic sacs, resulting in 60-70% MZ twins, risk of twin to twin transfusion syndrome (unequal blood share) |
| type of cell at day 4-8 | blastocyst |
| monochorionic-monoamniotic twins | same placenta + amniotic sac occurring when zygote splits after 9th day post fertilisation, resulting in 1-2% MZ twins with a 50-60% survival rate but umbilical cords may tangle around babies leading to miscarriage/cerebral palsy (lack of oxygen) |
| type of cell at day 8-13 | implanted blastocyst |
| issues with monochorionic-diamniotic twins | twin to twin transfusion syndrome (one receives less blood, other receives too much blood) |
| issues with monochorionic-monoamniotic twins | umbilical cord tangles = lack of oxygen = miscarriage/ cerebral palsy |
| conjoined twins | occurs if division of zygote occurs later than 12 days same placenta + amniotic sac with highest mortality rate as shared organs |
| type of cell at day 13-15 | formed embryonic disc |
| gastrulation | formation of germ layers: ectoderm, mesoderm, endoderm occurring by day 21 |
| ectoderm + mesoderm + endoderm together makes what | trilaminar disc |
| primitive streak | region of epiblast moving ectoderm cells down between ectoderm + endoderm layer to form intraembryonic mesodern (mesoderm) via epithelial-mesenchymal transition |
| epithelial-mesenchymal transition | non-mobile ectoderm cells become mobile mesoderm cells |
| prochordal plate | at region of the presumptive mouth, hypoblast cells become columnar + fuse with epiblast cells to form circular, midline thickening (no mesoderm between) |
| notochord | cell from rostral (head) end of primitive streak form midline structure which induces overlying ectoderm to form neuroectoderm of neural plate |
| mesoderm made from primitive streak goes where | migrates laterally (until it joins with extraembryonic mesoderm) + forwards over prochordal plate forming septum transversum |
| cloacal plate | similar to prochordal plate which will give rise to anal end of gut |
| neural plate forms what | neural folds (neuroectoderm) which eventually fuse to form neural tube (brain + spinal cord)+ loses contact of overlying ectoderm |
| implantation takes how long | 2 weeks |
| what is formed by 3rd week (21st day) | ectoderm, mesoderm, endoderm |
| ectoderm layer becomes | skin epidermis, epithelial lining of mouth + anus, cornea + eye lens, nervous system (basically covers of things) |
| mesoderm layer becomes | notochord, skeletal + muscular + circulatory + lymphatic system (systems) |
| endoderm layer becomes | epithelial lining of digestive tract + respiratory system, lining of urethra, liver, pancreas, thymus, thyroid and parathyroid glands |
| explain mortality in all twin types | highest in conjoined (as complications arrive from sharing organs) and lowest in DiDi. Survival rate is 50-60% in MoMo and there is risk of twin to twin transfusion syndrome in Monochorionic/ Diamniotic. |
Created by:
kablooey
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