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43 Cards in this Set
- Front
- Back
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What are the 4 Major events of Week 2 in embryogenesis?
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1. Implantation completed
2. Bilaminar disc forms 3. Amnion/yolk sac formation 4. Extraembryonic mesoderm forms |
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What stage is the uterus in when the free blastocyst is ready to implant?
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The Secretory Phase
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What primarily influences implantation of the blastocyst? Why?
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Estrogen and Progesterone - so that the embryonic and uterine developments are synchronized.
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When does implantation occur?
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Day 5-12
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What are the 2 phases of implantation?
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Phase 1: Attachment
Phase 2: Penetration/Embedment |
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What does the Attachment phase consist of?
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-Binding of the Blastocyst Embryonic Pole to receptors
-Decidual Reaction |
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What is the decidual reaction?
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The maternal recognition of pregnancy
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What three changes to the endometrium occur in the decidual reaction?
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-Endometrial thickening
-Stromal cell hypertophy -Blood flow increase |
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Why does the decidual reaction occur?
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To provide a dense Compact Zone of cells for blastocyst implantation.
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Where in the emryo is the Embryonic Pole?
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Where the Bilaminar disc is, above the fluid-filled cavity.
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On what days does the Attachment (phase 1) occur?
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Days 5-6
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On what days does the Penetration and Embedment phase occur?
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Days 6-12
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What happens to the blastocyst when it embeds within the endometrial compact zone?
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Cytodifferentiation
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What does the blastocyst differentiate into?
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-Syncytiotrophoblast
-Cytotrophoblast |
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What is synctiotrophoblast?
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a Mess of trophoblast cells lacking defined borders that invade the endometrium.
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What is cytotrophoblast?
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The original trophoblast cells; they retain their epithelial nature b/c they still ahve intercellular borders.
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What are lacunae?
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Spaces within the syncytiotrophoblast where garbage from gland/vessel invasion accuulates.
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What does the lacunae formation represent?
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Establishment of the uteroplacental circulation primordium.
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What condition results if the embryo implants too close to the cervix?
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Placenta previa
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What occurs in placenta previa?
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Premature placental detachment.
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What is the name for an extrauterine implantation?
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Ectopic pregnancy
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What is the estimated rate of ectopic pregnancy in the US?
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1/100 implantations
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Where does ectopic pregnancy usually occur?
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In the outer 1/2 of oviduct - Tubal PRegnancy
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What are the classic symptoms of a tubal pregnancy?
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-Spotty bleeding
-Severe abdominal pain -2.5 months |
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What factors cause tubal pregnancy?
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-Tubal infection
-Impaired motility -Premature ZP hatching |
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Other than intra/extrauterne implantations, what else can occur during implantation?
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Spontaneous abortion - Miscarriage
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What 3 major changes occur in the bilaminar disc during week 2?
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-Formation of Amnion
-Formation of Yolk Sac -Formation of Mesenchyme |
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What is the amnion?
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An extraembryonic membrane that will eventually cover the embryo
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where does the amnion form?
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Above the epiblast in a dorsal cavity.
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What does amnion tissue derive from?
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Epiblast
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Where does the Yolk sac form?
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In the cavity formly just a fluid-filled cavity.
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What does the yolk sac form from?
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Migrating hypoblast cells
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What is the yolk sac?
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An extraembryonic membrane that metabolizes/transports nutrients from the trophoblast -> embryo
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What happens to PGCs in the yolk sac?
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They segregate there.
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what is extraembryonic mesenchyme?
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The 2nd type of tissue to differentiate in the embryo (the first was epitheilum)
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What is mesenchyme?
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"nonpolarized, free cell derivative of an embryonic epithelium which is often mobile". Aka, mesoderm
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Where does the extraembryonic mesoderm form?
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Between the epiblast and hypoblast; then migrates out around yolk sac.
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What causes mesenchyme formation?
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Epithelial/mesenchymal transformation.
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What changes to epithelial cells are necessary to form mesenchyme?
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1. Lose polarity, change shape
2. Downregulate CAMS (cell) 3. Upregulate SAMS (substrate) 4. Extend processes for binding ECM substrate |
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What is Chorion?
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The name for both Trophoblast + Extraembryonic Mesenchyme
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Why is the chorion important?
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Because it surrounds what's now called the chorionic cavity; this surrounds the 2ndary yolk sac.
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What is the Body stalk?
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A condensed portion of EEM (extraembryonic mesenchyme) that suspends the emryo at its posterior end (dorsal) within the chorionic cavity.
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What will the body stalk become?
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The umbilical cord, with umbilical vessels.
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