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9 Cards in this Set
- Front
- Back
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where does fertilization occur |
-ampulla of the oviduct -implantation occurs in the uterus ~5 days after fertilization |
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how do eggs reach the site of fertilization |
-egg is released from the ovary and enters the oviduct via ciliary action |
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how do sperm reach the site of fertilization |
-motility propels them -E2 during follicular phase of the ovary causes: uterine mucus to be watery and form channels that sperm can move through easily and peristaltic contractions of the uterus -bind isthmus and become hyperactive (changes swimming pattern) -maybe chemotaxis |
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what changes occur in sperm to allow fertilization |
capacitation includes: -altered membrane fluidity (removal of cholesterol) -removal of proteins and carbohydrates -change in membrane potential (more neg) -protein phosphorylations -bind to the isthmus of the oviduct and become hyperactivated (change swimming pattern) |
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timing of fertilization |
-egg is ovulated 24-48 hrs after LH surge -ovulated egg only survives about 24h -sperm can survive for days -if insemination occurs in the two days preceding ovulation the probability of fertilization is about 35% -about 2/3 of fertilized eggs develop into successful pregnancy |
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how do sperm and egg nuclei come together |
-recognition is mediated by sperm's izumo and egg's juno -entire sperm enters egg, its mitochondria and tail disintegrate; centriole and nucleus remain -sperm nucleus decondenses --> male pronucleus -centriole organizes a MT aster, which contacts the female pronucleus -DNA replication during migration (12hrs) -pronuclei fuse and cell undergoes mitosis |
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polyspermy |
-more than 1 sperm entering an egg -always lethal --> 10-15% of spontaneous abortions -prevented by exocytosis of cortical granules (in response to increased Ca++) that contain enzymes to modify ZP2 and ZP3 --> removes sperm that are already bound and prevent further binding |
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signal for sleeping egg to begin development |
-likely mechanism: sperm introduces PLC, which cleaves PIP2 --> cascade causing release of Ca++ from endoplasmic reticulum -triggers a series of repetitive Ca++ oscillations that can last for hours -Ca++ triggers completion of meiosis and release of cortical granules that prevent polyspermy |
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sperm's path to the egg |
-capacitated sperm can get through cumulus cells due to the hyaluronidase enzyme (PH20) -bind the ZP protein ZP3 --> opening of Ca++ channels --> sperm undergo acrosomal reaction = exocytosis of the large secretory vesicle in the anterior portion of the sperm -enzymes in the acrosome allow the sperm to penetrate the ZP and bind ZP2 |
