Flashcards in 12 - Fertilization Deck (39):
What are gametes and What is the process by which they are made called?
Specialized cells produced in the ovaries and testis by the process of gametogenesis.
They have a haploid number of chromosomes and participate in cell fusion during fertilzation.
What is gametogenesis called in the makes and females?
Spermatogenesis and oogenesis.
Describe mature sperm and how they travel.
Small cells with strong flagellum that allows them to travel 22 microm/sec.
Transported in fluid called semen.
What are sperm designed for?
Penetration of oocyte coverings, which is mediated by enzymes released from the acrosome - a lysosome-like organelle that covers the sperm nucleus.
Designed to deliver haploid genome in form of compact nucleus.
What are the two types of sperm?
X and Y.
What is the structure of an ovulated oocyte (ovum)?
One of the largest cells in the body- designed for supporting and sustaining embryonic development.
Abundant cytoplasm with organelles that store important molecules needed for embryonic development
Divides after diploid chrom number is restored.
What are the coverings of the oocyte from outermost to innermost?
Zona pellucida: acellular containing proteins ZP1-ZP4
Oocyte plasma membrane
What are three clinically significant problems that can occur in the production of gametes?
1. Morphological abnormalities that affect the sperm and oocytes.
2. Chromosomal abnormalities such as nondisjunction during meiosis or translocations
3. Advanced parental age can cause overripe oocytes.
What two things can the abnormal production of gametes cause?
1. Preventsgametes from participating in fertilization (infertility)
2. Abnormal gamete participating in development can cause birth defects (and premature birth).
Where does fertilization usually occur? How long are oocytes and sperm each viable for?
The outer third of the ovoduct in the ampulla (only about 200-500 sperm make it to sight of fertilization).
Ooctyes viable ~24 hrs
Sperm viable ~3-5 days
What is the journey of the sperm in a male?
Testis - epididymis (matures here and becomes motile) - vas deferens - ejaculatory duct - urethra
What are things that can prevent the sperm from getting to the point of fertilization? How do sperm combat these issues?
Low pH in the vagina can cause the sperm to die - semen can buffer this low pH
Sperm can get lost in the folds of the cervix - mucous is watery here during ovulation so sperm can more easily move through
They can go in the wrong tube - an ovum is only released from one ovary at a time
Where are sperm deposited in woman? What needs to happen next?
They are held at the isthmus and can bind epithelial cells that line the ovoduct.
Sperm are not yet mature, they have to go through another phase before fertilization can occur.
What is the journey of the ovulated oocyte?
Release from ovary into peroneal cavity.
Presence of cumulus (follicle) cells surrounding oocyte allow cilia on fimbrae to drive the oocyte into the lumen of the ovoduct.
What needs to happen when the sperm gets to the oocyte for fertilization to occur?
Sperm needs to get through the coverings on the oocyte.
What is the first step of fertilization?
-occurs in female fluids, sperm membrane changes to increase sperm metabolism and hypermobility.
The first step fertilization is also the last step of _____?
Maturation of the sperm.
What is the second step of fertilization? Where does this occur?
The acrosome reaction: Occurs before sperm encounters the cumulus mass.
Describe the steps of the acrosome reactions (step 2 of fertilization)?
Fusion of sperm PM with outer acrosomal membrane to create a group of small vesicles.
Membrane vesicles are shed to expose the acrosome enzymes, some of which are boudn to the inner membrane.
Involves Ca mediated signaling.
What is the third step in fertilization?
Binding of sperm to the Zona Pellucida (ZP):
Receptor-mediated event in which sperm bind to ZP2 molecule on the oocyte, which is mediated by Sed1, a protein on the surface of the sperm's head.
What is the fourth step of fertilization?
Penetration of the zona pellucida.
Acrosome enzymes (acrosin) hydrolyze ZP glycoproteins, allowing sperm to pass through this acellular protein coat.
Movement of tail facilitates ZP penetration.
What is the fifth step of fertilization?
Fusion of sperm and the oocyte cell membranes.
Sperm enters perivitelline space can access oocyte PM. Sperm PM near base of head that wasn't shed during acrosome reaction can fuse with the oocyte membrane.
What proteins are involved in the fusion of the sperm with the oocyte membrane (step 5 in fertilization)?
Fertilin B (adam2) on the sperm membrane binds to integrin on the oocyte membrane - thought to be modulated by CD9 on the oocyte
Sperm related fusion factor (zumo) also binds juno on the oocyte membrane.
Only _____ sperm can participate in membrane fusion.
What happens after fusion of sperm and oocyte (stage 5 of fertilization)?
Sperm motility stops.
The head, midpiece, and tail (usually) enter the oocyte cytoplasm.
Cell membrane of sperm is encorporated into oocyte cell membrane.
What is the sixth step in fertilization? What are the first three steps of this?
1. Wave of Ca causes transient hyperpolarization of oocyte PM which may initially block polyspermy.
2. Cortical reaction: oscillations of Ca stimulate fusion of cortical granules with oocyte PM, causing hydrolytic and oxidative enzymes release into PV space.
3. Zona reaction: cortical granule enzymes enter ZP and crosslink it's glycoproteins to prevent sperm binding/penetration.
What are the last two steps of oocyte activation (6th step of fertilization)?
4. Ca deactivates meiotic inhibitor and oocyte finishes 2nd meiotic division. 2nd polar body is extruded and haploid female pronucleus forms.
5. Sperm chromatin decondenses and male pronucleus (haploid) forms.
What is the seventh step of fertilization?
Nuclear membranes of male and female pronuclei breakdown and chromosomes form a metaphase plate.
This union of paternal and maternal chromosomes is a diploid cell called a zygote.
This initiates first mitotic division.
If fertilization has occurred, then what has been accomplished?
Two pronuclei are in the oocyte cytoplasm
Two or three polar bodies are in the perivitelline space
Remnants of a sperm flagellum is in the oocyte cytosplasm.
What are the results of fertilization? What is the next step in development after fertilization?
Oocyte completes meiosis
Diploid chromosome number restored (genetic diversity generated)
Sex is determined (by the type of sperm)
Next step: cleavage
Why are the haploid genomes of male and female gametes not equivalent? Why is this?
Expression of the alleles of some maternal and paternal genes is not the same during embryonic development.
Due to genomic imprinting.
What is the function of genomic imprinting? When does it occur?
Allows sex specific non-equivalent expression (male or female) of alleles during embryonic development.
Occurs during gametogenesis.
What is parthenogenesis? Does it occur in humans?
Oocyte activation without a sperm; does not occur in humans.
What is a Hydatidiform Mole? What is it caused by?
An intrauterine tumor.
Occurs when an oocyte has two paternal genomes and no maternal genomes.
This is an example of genomic imprinting.
Other than a Hydatidiform mole, what is a second example of genomic imprinting?
The insulin-like growth factor (IGF2) male derived allele is expressed during embryonic development and in the adult while the female derived allele is silent.
On the other hand the receptor is a female derived allele and is expressed.
What are the steps of in vitro fertilization and embryo transfer (IVF-ET)?
1. Stimulation of ovulation
2. Collect oocytes
3. Obtain sperm
4. capacitate sperm
5. incubate gametes
6. develop embryos to blastocysts
7. implant blastocysts in uterus (usually 3)
If three blastocysts are implanted with IVF-ET, what percentage of attempts are successful? What percentage of successful implantations reach full term?
~19% are sucessfull
~80% of successful implantations reach full term
What appears to be the weakest link of IVF-ET?
The embryo transfer step.