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31 Cards in this Set
- Front
- Back
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3 germ layers
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-ectoderm
-mesoderm -endoderm |
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first few steps in spermatogenesis/oogenesis
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1) primordial germ cells appear in the posterior wall of the secondary yolk sac at end of 3 weeks
2)about 1000 PGC's migrate to where the gonads will be and undergo rapid mitotic division 3)pattern of mitotic proliferation differs in males and females |
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teratomas
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-misdirected PGC's; usually die, but sometimes they survive
-bizzare growth that contain mixtures of highly differentiated cells -unique problem with embryonic stem cells |
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spermatogenesis
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-PGC's migrate to gonads
-PGC's (spermatogonia) proliferate into primary spermmatocytes -undergo meiosis I --> 2 secondary spermatocytes -undergo meiosis II --> 4 spermatids -go through spermiogenesis --> 4 mature spermatozoon (sperm cells) |
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oogenesis
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-PGC's differentiate into oogonia --> further differentiate into clusters of oogonial cells
-proliferate (mitosis) through the 5th month to reach nearly 7 million PGC's -proliferation stops and atresia (degeneration begins) until menopause -by 7th month, PGC's either degenerate or differentiate into primary oogonia surrounded by follicular cells -2 million primary oocytes at birth --> 40,000 by puberty -oocytes being meiosis I, but become blocked (each month some release and continue meiosis) -5-12 oocytes complete meiosis (only one egg is ovulated; the rest die) -mature oocyte begins meiosis II --> but is blocked at second metaphase just before ovulation -completes meiosis II after fertilization |
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fast & slow block to polyspermy
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-sperm attaches & fuses with the zona pellucida
-sperm releases enzymes from head to help penetrate ZP -fusion of sperm with egg membrane -sperm/egg fusion --> wave of calcium blocks membrane -cortical reaction --> granules release content --> zona reaction -zona reaction --> polymerization of ZP glycoproteins prevents further sperm access to egg -2nd meiotic division of egg occurs and 2nd polar body excluded -sperm nucleus decondenses and egg nucleus both form pronuclei about 4-5 hours after initial activation of egg |
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zona pellucida lost...
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when blastocyst hatches from it prior to implantation
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cleavage of zygote
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-1st Cleavage forms blastomers (daughter cells of original zygote)
-cleavage (mitosis) of zygote --> forms morula -morula --> blastocyst with inner cell mass and surrounding trophectoderm cell layer -blastocyst hatches from ZP -implantation occurs |
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placenta
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-structural interface that facilitates exchange of nutrients & waste between mother and fetus
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inner cell mass
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-becomes the embryo proper --> ectoderm, mesoderm, endoderm --> organs, tissue ect
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embryonic stem cells
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-undifferentiated cells of the inner cell mass
-most breakthroughs occur with adult stem cells (already partially committed) -work with embryonic stem cells often lead to teratomas. |
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eggs ovulated over a lifetime
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usually only 500 eggs are ovulated from puberty to menopause
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ectopic pregnancy
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-blastocyst implants somewhere other than uterus
-can lead to major complications |
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embryonic period
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-fertilization to end of 8 weeks
-all organs present at that time, just grow & develop after |
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fetal period
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9th week to birth
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blastocyst cavity
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fluid filled cavity that forms in ICM
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implantation
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-typically occurs with embryonic pole of embryo implanting in wall
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3 cell layers at embryonic pole
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trophoblast, epiblast, & hypoblast cells
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trophoblast develops into...
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syncytiotrophoblast & cytotrophoblast
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syncytiotrophoblast
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infiltrates uterine wall during implantation
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why is embryo not rejected as foregin material?
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elaborate set of mechanisms during implantation where embryo is masked from the female’s immune system
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ab-embryonic pole
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pole opposite the embryonic pole
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amniotic cavity
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-begins to form between epiblast & cytotrophoblast
-fills with fluid secreted by epiblast |
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eventually cytotrophoblast completely covered by...
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syncytiotrophoblast
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trophoblastic lacuna
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-fluid filled spaces in the syncytiotrophoblast
-eventually fill with blood from mother |
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the hypoblast begins to proliferate & migrate...
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-over the inside surface of the cytotrophoblast to form the Heuser’s membrane of the blastocyst cavity
-name of blastocyst cavity changes to primary yolk sac |
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REVIEW NOTES
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for overall process of bilaminar germ development
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after primary yolk sac...
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-then form definitive yolk sac
-also formation of chorionic cavity -extraembryonic reticulum forms -extraembryonic membrane extends from epiblast -eventually remnants of primary yolk sac break off and dissipate into extraembryonic membrane at abembryonic pole |
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chorionic cavity
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-enclosed by extraembryonic membrane
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as amniotic cavity expands it begins to fill...
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-the chorionic cavity
-embryo will be covered with the amniotic cavity |
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progressive development of placenta
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-develop from primary to tertiary villi
-nutrients pass from mother’s blood vessels through the villi to emrbyo -waste passes back through the villi and back into mother’s circulation -villi are exchange interface between mother & embryo -all blood vessels extend through the connecting stalk |
