Embryogenesis Flashcards
Fertilization usually occurs in the ________ of the oviduct within 24hrs of ovulation
ampulla
Series of cleave and differentiation events results in the formation of a __________ by the 4th embryonic day
blastocyst
______________ of the blastocyst generates embryonic tissues
Inner cell mass (ICM)
Outer ___________ of blastocyst generates placental tissues
trophectoderm
____________ into the uterine wall occurs ~6th embryonic day (day 20 on menstrual cycle)
Implantation
Clear zone of the egg, on the periphery
Zona pellucida
Layer around the egg that provides nutrients
Larger and is easier to be captured by cilia to allow transport
Corona radiata
______________ classify pregnancy as:
fertilization egad: moment of fertilization is d0
Division of pregnancy corresponding to development
Total gestation time = 38 weeks
Embryologists
______________ classify pregnancy as:
Menstrual age: first day of menses is d0
Division of pregnancy into trimesters
Total gestation time = 40 weeks
Clinical time really two weeks later
Clinicians
Sperm have _______ receptors
100s bind to the egg, but only one manages to contact the oollemma
ZP (zona pellucida)
Fusion of sperm and egg membrane induces __________
Ca2+ influx and cortical reaction occur
Depolarization
Cortical granules fuse with oollemma and release enzymes that digest ZP proteins so other sperm can no longer bind
Triggered by Ca2+ influx and depolarization
(hyaluronic acid and other proteoglycans are also released that become hydrated and swell, thus pushing the other sperm)
Cortical reaction
Polar bodies are seen in the newly fertilized egg as evidence of:
meiosis (meiosis II not completed until fertilization)
Successive splitting into smaller cells via mitosis (don’t grow cell size - just increase number of cells)
Goal: transform unicellular zygote into multicellular embryo
Cleavage
During week 1, individual cells are called ___________ and are equivalent to each other (totipotent - can generate both embryo and placenta)
blastomeres
Embryo undergoes _________ after 8-cell stage: first differentiation of embryonic lineages
compaction
During compaction, there is increased cell-cell adhesion due to increased expression of ________ that allows segregation of cells
cadherin
Cells that are forced to the outside of the compacted _________ are destined to become trophoblast (placenta) and the inner cells will form the embryo proper (ICM)
morula
During formation of the blastocyst, fluid is pumped into the embryo for the cavitation of the embryo
The cavity is called then ____________
blastocoele
During formation of the blastocyst, ________ channels appear on the surface of the outer trophoblast cells
Sodium and water are pumped into the forming blastocoele (embryo still contained in zone pellucida)
sodium
Hatching of the embryo from the zone pellucida occurs just prior to __________
implantation
Inability to hatch from ___________ in preparation for implantation results in infertility, and premature hatching can result in abnormal implantation in uterine tube
zona pellucida
Implantation somewhere other than upper portion of uterus
Rupture can lead to life-threatening hemorrhage
Ectopic pregnancy
Ectopic pregnancies typically occur in the __________ region
ampullary
During week 2 (implantation), a ___________ embryo develops, along with the amniotic cavity and yolk sac
bi-laminar
During implantation and placentation, the trophoblast differentiates into _______________, which is the stem cell population
Cytotrophoblast
During implantation and placentation, the trophoblast differentiates into _______________, which is invasive fused cells (syncytium -multi-nuclei) derived from the cytotrophoblast
Syncytiotrophoblast
During implantation and placentation, the trophoblast differentiates and breaks maternal capillaries, causing trophoblastic ________ to fill with maternal blood
lacunae
During implantation and placentation, the inner cell mass divides into:
Epiblast
Hypoblast
The ________ derived from ICM contributes to forming the overlying amniotic membrane and amniotic cavity
(all embryonic structure - dorsal)
Epiblast
The _________ derived from ICM contributes to forming the underlying yolk sac (ventral)
Hypoblast
The _____________ derived from the trophoblast invades maternal tissues by hitting maternal blood vessels, blood spills in, fusion of maternal and fetal blood (diffusion, not direct mixing)
Substances can cross (before mother knows she is pregnant - alcohol, etc.)
Syncytiotrophoblast
The _________ allows for exchange (not mixing) between maternal and fetal blood
placenta
Early placental barrier (1-12 weeks) has more layers:
Syncytium
Cytotrophoblast
Embryonic CT
Endothelium
Later placental barrier (4th month - term) has fewer layers:
Syncytium
Endothelium
