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74 Cards in this Set

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