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74 Cards in this Set
- Front
- Back
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What are the participants in conception?
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-Spermatozoa
-Ovulated oocytes (the ovum) |
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What features of spermatozoa aid in conception?
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-Motility
-Designed for penetration of oocyte -Designed to deliver compact nuclear contents. |
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What makes sperm motile?
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-Streamlined
-Strong flagellum - travel at 22um/sec -Fluid transport medium (semen) |
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How long does it take sperm to reach the uterine tube?
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Can be as fast as 5 min after being placed in the cervix.
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What are the layers of a sperm's head?
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-Plasma membrane
-Outer acrosomal membrane -Inner acrosomal membrane -Nucleus |
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What features of the ovum aid in conception?
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-Design for support/sustenance of developing embryo
-Can divide after 2N restored -Coverings |
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What are the contents of the ovum?
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The stored goods for the developing embryo - mRNA, rRNA, nutritional reserves, organelles.
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What are the coverings on an oocyte?
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-Follicle cells (aka cumulus)
-Zona pellucida (ZP1/2/3) -Cell membrane |
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Where is the normal site of fertilization?
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Outer 1/3 of the uterine tube.
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What happens during the process of fertilization in general?
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-Millions of sperm are deposited in ejaculate, but only a few reach the outer 1/3 of tube.
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How long are each viable:
-Oocytes -Sperm |
-Oocytes viable 24 hrs
-Sperm viable 3-5 days |
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What does fertilization of overripe ova result in?
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Spontaneous abortion
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Describe the journey of the sperm in the male reproductive tract:
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-Testis -> epididymis -> through duct system.
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What happens to sperm in the epididymis?
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They mature, become motile, and increase metabolism.
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List 4 points of the sperm's journey through the female reproductive tract:
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-Vagina
-Cervix -Uterus -Oviduct |
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How does the vagina act as a barrier to sperm transport?
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low pH, sperm antibodies
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How does the cervix act as a barrier to sperm transport?
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Dead ends in mucosal folds, unfavorable mucus consistency.
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How does the uterus act as a barrier to sperm transport?
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The sperm can get lost and enter the wrong oviduct.
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How does the oviduct act as a barrier to sperm transport?
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The sperm are stored in the isthmus portion.
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What do sperm encounter when they get to the oocyte?
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Its many layers - Cumulus cells, ZP, perivitelline space, plasma membrane.
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What does the oocyte's journey consist of?
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It is short and relatively rapid - fimbriae grab at it and waft it into the fallopian tube.
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How are oocytes released from the ovary?
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The follicles rupture and release it into the infundibulum and fimbriae.
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What layer of the ovum aids in its transport after release?
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Sticky cumulus cells help fimbriae to grab at it.
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How many steps are involved in fertilization?
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7
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What are the 7 steps of fertilization?
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1. Capacitation
2. Sperm binds ZP 3. Acrosome reaction 4. ZP Penetration 5. Fusion of sperm/oocyte cell membranes 6. Oocyte activation 7. Zygote formation |
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What is capacitation really?
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The last step in sperm maturation; but also the first step in fertilization.
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What are the key features of Capacitation?
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-Female tract fluids activate sperm while stored in oviduct isthmus
-Changes occur in sperm plasma membrane preparing for acrosome rxn. |
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What changes occur in the sperm during capacitation? (2)
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1. Metabolic activity increases
2. Sperm becomes hypermobile |
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What type of event is sperm binding to ZP?
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-Receptor mediated
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What are the sperm receptors on the zona pellucida?
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ZP2 and ZP3
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What feature of a sperm is essential for its binding ZP?
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It must have an INTACT ACROSOME.
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What molecule on the sperm membrane allows it to be bound by ZP2 and ZP3 on the ovum?
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We're not sure.
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What is the 3rd step in fertilization?
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Acrosome reaction.
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When does the Acrosome reaction occur?
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Seconds to minutes after the sperm binds the ZP
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What is the acrosome reaction mediated by?
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Zona pellucida proteins -
ZP2 and ZP3 - they really trigger the acrosome reaction. |
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List the 3 steps that occur in the acrosome reaction:
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1. Sperm plasma membrane fuses with outer acrosomal membrane.
2. Created vesicles are shed, exposing acrosome enzymes. 3. Secondary ZP binding holds sperm to ZP during penetration. |
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What mediates the acrosome reaction?
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Calcium mediated signalling pathways.
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What allows for sperm to penetrate the zona pellucida?
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-Acrosomal enzymes released during step 3.
-Sperm flagellum movements |
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What is step 5 of fertilization?
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CBAPFOS... F=Fusion of membranes
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Where on the sperm membrane does fusion with oocyte membrane occur?
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Just behind the equatorial region.
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How specifically does fusion occur?
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Fertilin on the sperm membrane binds Integrin on the oocyte.
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What is specifically required of sperm in order to be able to fuse with the oocyte?
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The acrosome MUST BE REACTED.
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What happens to sperm motility after membrane fusion?
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It stops.
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What parts of the sperm enter the oocyte after fusion?
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-Head
-Midpiece -Tail (membrane fuses with oocyte membrane) |
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What is step 6 of fertilization?
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Oocyte activation
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What are 5 key features of the Oocyte activation step?
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a. Fusion initiates intracellular Ca2+ oscillation
b. Cortical reaction c. Zona reaction d. Meiosis completion e. Presence of male/female pronuclei |
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What is the purpose of intracellular Ca oscillations?
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It hyperpolarizes the oocyte cell membrane and blocks polyspermy.
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What characterizes the Cortical Reaction?
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Release of hydrolytic and oxidative enzymes in Cortical Granules -> also caused by calcium oscillations.
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Where are the cortical granules released during the cortical reaction?
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Into the Perivitelline space between the ZP and oocyte membrane.
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What is the purpose of enzymatic cortical granules?
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To facilitate the Zona reaction.
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What is the zona reaction?
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Crosslinking of Zona glycoproteins to prevent further sperm penetration.
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What allows the oocyte to complete meiosis? What is it now called?
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Ca2+ ions deactivate a meiosis inhibitor. The oocyte is now an ootid.
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What is present at the end of the oocyte activation step?
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-Male and Female pronuclei; they both lose membranes, undergo DNA replication.
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What is the 7th and final step of fertilization?
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Zygote formation.
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What does Zygote formation entail (2 things)?
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-Formation of a Metaphase plate by the chromosomes
-Mitosis - the first cleavage of the zygote. |
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How can you tell if fertilization has occurred?
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-2 pronuclei are in cytoplasm
-2 or 3 polar bodies in perivitelline space -Remnants of a sperm flagellum will be in the ooplasm. |
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What are the 4 results of fertilization?
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1. Oocyte completes meiosis
2. Diploid chromosome # restored 3. Sex is genetically determined 4. Cleavage is initiated. |
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What is parthogenesis?
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The activation of an oocyte without a sperm.
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Does parthogenesis occur in humans?
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No
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Why are both parents needed for conception?
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Because the male and female haploid genomes are not EQUIVALENT; some alleles are expressed more by one than the other and vice versa.
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What is the unequal allelic expression of haploid genomes by male/female gametocytes called?
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Genetic imprinting.
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Give the proper definition of genomic imprinting:
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Differential expression of male and female alleles of a gene that occurs during gametogenesis.
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Can you cite 2 examples of genomic imprinting?
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-Hydatiform mole
-Insulin growth factor 2 (IGF2) |
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What is a hydatidiform mole?
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A tumor formed when an oocyte has 2 paternal genomes and no maternal genome.
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How is IGF2 (insulin growth fx) an example of genomic imprinting?
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The male allele for this gene is expressed during development, but the female gene is not.
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What % of couples experience infertility?
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About 15%
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What is IVF-ET?
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In vitro fertilization and embryo transfer
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What are the steps in IVF-ET?
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1. Stimulate ovulation
2. Collect oocytes 3. Obtain sperm 4. Capacitate sperm 5. Incubate gametes 6. Develop embryos to blastocyst stage 7. Implamt blastocyts in uterine wall |
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What is the success rate of IVF-ET?
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If 3 embryos implanted, 19% successful; 80% reach full term
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What is the weakest link in IVF-ET?
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the Transfer process - embryo transfer
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What are the side effects of IVF-ET?
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-Increased inc. multiple pregn.
-Spontaneous abortions -Ectopic pregancy -NOT increased birth defects |
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What are 2 alternative methods to IVF-ET?
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1. Gamete intrafallopian transfer (GIFT)
2. Zygote intrafallopian transfer (ZIFT) |
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What is GIFT?
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Gametes collected and place into uterine tube
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What is ZIFT?
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Zygote is producd by IVF, then placed into oviduct.
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