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43 Cards in this Set

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