Fertilization, Cleavages And Implantation Flashcards
List of the four major fertilization events
Contact and recognition between sperm and egg
Regulation of sperm entry into the egg
Fusion of the genetic material
Activation of egg metabolism
What are cumulus cells?
Cells that surround the oocyte in the follicle and after ovulation
What are the roles of the cumulus cells?
Protection, development, fertilization
What are corona radiata cells?
Part of the cumulus, innermost layer surrounding the oocyte
What is the Zona pellucida?
A matrix that surrounds the oocyte
What is the role of the Zona pellucida?
Binds spermatozoa, species specific barrier
List the changes in cumulus-oocyte complex of rabbits during follicular maturation and ovulation
In pre-ovulatory follicle, cumulus cells are tightly packed around the oocyte
Pre-ovulation, luteinizing hormone, stimulates the follicle
Cumulus cells produce extracellular, matrix, becoming more spread out by ovulation
Is the ovulated oocyte still surrounded by cumulus cells?
Yes
How many sperm are ejaculated into the vagina in humans?
About 200 to 300,000,000
About how many sperm enter the oviduct
About 400
How many sperm choose the wrong oviduct
200
What is sperm motility crucial for?
Getting the sperm from the vagina through the cervical mucus and into the uterus
How is sperm transported into the ducts?
Uterine contractions
What are sperm associations?
In species with promiscuous females, sperm from the same male form aggregate, enabling them to swim faster due to increased flagella or propulsion.
What is sperm capacitation?
A final set of biochemical events that change the sperm to enable fertilization of the egg
List the three signals secreted by the oviduct for sperm capacitation
Cholesterol is removed, possibly in increasing sperm membrane fluidity
Glycol proteins are lost, which may expose Zona binding proteins
Fluctuations in intracellular calcium levels, which is essential for sperm hyper activation
List five effects of capacitation
Hyper activation
Increased rate of metabolism to meet the needs of active sperm
Changes in sperm glycoproteins to prepare for sperm egg binding
The enzyme pro-across in ((inactive)) is converted to acrosin [active)
Increased thermal and chemical sensitivity, which helps the sperm find the egg at the end of the oviduct
How does thermal sensitivity help sperm find the egg?
There is a thermal gradient of 2°C along the oviduct, with the egg at the warmest end
The sperm can sense these differences and tend to to move toward the highest temperature
How does chemical sensitivity help the sperm find the egg?
Cumulus cells, secrete, progesterone, which attracts sperm
What five things happen after sperm enters the egg
The egg is activated by calcium influx
The egg is released from metaphase two
The male pro nucleus is de condensed
The Zona hardens to prevent polyspermy
Zinc, spark
What is zinc, spark
Billions of zinc ions are released upon sperm entry into the egg
This prevents polyspermy by inhibiting acrosin enzyme activity
What does sperm contribute?
The pro nucleus
The centrosome which is required for cleavage
And the tail which is incorporated into the plasma membrane
Describe metabolic egg activation
Waves of calcium pass through the cytoplasm from the side of fusion stimulating completion of the second meiotic division
Calcium ions will cause cortical granules to fuse with the plasma membrane
And later calcium ions will initiate recruitment of maternal RNAs
Outline the seven steps of in vitro fertilization
Hormonal stimulation of egg maturation
Removal of eggs by laparoscopy
Collection of sperm sample, and concentration of the most active sperm
In vitro fertilization
Early cleavage in vitro
Extra embryos frozen
Re-implantation of up to three of the embryos
How has in vitro fertilization evolved?
Such that sperm is injected directly into the egg
When does the first cleavage occur?
About 24 hours after fertilization
How much time does it take between each cell division?
About 12 to 24 hours
At what day is the two cell stage?
Day one
How many days does it take to get to the four cell. stage
Two days
How many days does it take to get to the nine cell stage?
2.5 days
How many days does it take to get to the 16 cell stage?
Three days
What is the name of the 16 cell stage?
The morula
How many days does it take to get to the 58 cell stage
Four days
How many days does it take to get to the 107 cell stage
Five days
What is the 58 cell stage called? Same for the 107 S. stage.
Blastocyst
When does compaction occur?
At the eight cell stage
What is compaction?
When cells are still separated, but adhere more tightly together
What causes compaction?
E-Catherine cell adhesion protein
How is the blastocoele formed?
From fluid appearing in blastomeres during cavitation, causing sodium and water to enter
When does cavitation begin?
About four days after fertilization
Describe hatching of the human embryo
Cells of the blastocyst secrete proteases
Which digest the zone of proteins
Causing the blast assist to hatch out of the Zona and the embryo escapes
When does hatching occur?
Before implantation
How is hatching related to infertility?
Inability to hatch is one cause of infertility
What might cause an inability to hatch?
Altered ZP
Absence of proteases
What are the two reasons for the ZP being present during early cleavages?
Protect protection and to prevent immature embedding
What does the ZP protect against?
Physical dangers and immuno responses
What is the possible cause of ectopic pregnancies?
Premature hatching
Where do the major majority of ectopic pregnancies occur?
In oviduct (96%)
List the five implantation events
Apposition of blastocyst to endometrial epithelium
Adherence of the blastocyst via solid adhesion molecules
Formation of SYNCTIO trophoblast
Penetration
Decidual reaction
What is the synctiotrophoblast?
A giant multinucleate cell that surrounds the complete embryo produced by the fusion of Cito tropho blast cells
How does penetration occur?
Synctiotrophoblast is invasive and works its way into the uterine tissue
What is the decidual reaction?
Uterine tissue responds to invasion by setting up an immunological barrier called the decidua
