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Developmental Biology II

Developmental Biology II - A Stages of Development 1...

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Developmental Biology II 21:45 A. Stages of Development 1. Fertilization 2. Cleavage 3. Blastulation 4. Gastrulation 5. Organogenesis 1. fertilization Syngamy – at end of acrosomal reaction, cell membranes fuse o Plasmogamy occurs normally in the first third of the ovaduct. – fusion of membranes. Secondary oocyte moves through the ovaduct by the movement of the cilia lining the ovaduct to the uterus. Egtopic pregnancy: when an oocyte is fertilized outside of the ovary Can occur due to many reasons, such as drug use. Drug use effects the cilia which cause scarring, decreasing motility – not allowing the egg to get through. o Polyspermy - BAD Polyploidy occurs when one more sperms gets into the egg. 1. Fast (Electrical) block: (after membranes fuse) Ca2+ influx, depolarization – depolarizing egg cell membrane depolarizes and sperm can not fuse while egg cell membrane depolarizes. keeps the sperm from getting to the egg (now secondary oocyte) In place in 1-3 seconds. – fast because But repolarization occurs in about 1min. 2. Slow Block: takes over from fast block -permanent! “cortical reaction” – what happens in secondary oocyte to block other sperms, put up a slow block. After plasmogamy this makes vesicales perform exocytosies and secrete cortical grandles dumped into the perivitelline space. A lot of solute dumped there is hypertonic solution – pushes wall further out and building a mote.
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Solutes biochemically change P space to fertilization membrane to block poly sperm. Usually takes about 1 minute.
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