Lecture 9 - Fertliziation and Implantation Flashcards
What does LH do to the oocyte
Primary oocyte is in prophase 1 , however with increases LH, get the meiosis occurring up until metaphase 2.
At ovulation, the egg consists of an oocyte and a small polar body surrounded by zone pellucida
-meiosis is resumed during fertilization
How does sperm get to fallopian tube where it is fertilised?
- after prostate and seminal fluids mix in the vagina, a coagulation will form to keep the sperm up there
- this dissolved called liquefaction after a few minutes, and allows the sperm to move away
- ph of vagina is low, this inhibits sperm mobility and survidial so the seminal plasma buffers the vagina pH to around 7.2 so sperm can become motile
Vaginal mucous
- a short time in perivodualtion the cervical mucousa becomes thin and volumous
- however otherwise it is viscous and
sperm tails beat and cause cerival mucous to vibrate, failure to do this - sperm cannot get into cervix.
-sperm cannot survive long in low pH of vagina
natural contraception
hard to date to when ovulation may occur
ashume sperm can live 5 days
immune response
- innate immune response
- leucotyes phagocytose dead or dying sperm
What is capacitiation, how does this help sperm?
Sperm are still not fully ready to fertlise an egg yet even when in vsagina
- need capacitation which ocurs in female reporductive tract
- removal of capacitation ihibitory susbtances form the sperm e.g cholesterol
- the sperm become hyperactive - can move tail alot more, can get around things easier
- can also undergo the acrosome reaction
Acrosomal reaction
-Acrosome contains - enzmes and protienases
-During this reaction, the acrosomal and plasma membrane of sperm head fuse and released the cotnents into the enviornemtn
-this is triggered by an influx of calcium into the cell
-can be triggered by progesterone, or zona pelucida Z3
-must occur in close proximity for sperm to beable to fertlise the egg
-
Fertilization
- Sperm must penetrate the cumulus cells that surround the egg
- hyaluronidase secreted from acrosome, digests the basement membrane and allows sperm to squeeze between the cumulus cells
- then sperm must get through corona radiata and digest through the zona pellucida
- ZP3 protein of zona pellucida will further induce the acrosomal reaction completely
-Sperm attatchtes to the oolemmaml membrane and the two membranse fuse allowing the sperm nucleus to enter the ovuum
Cortical reaction
entry of sperm into oocyte causes a release of intracellular calcium - followed by regular spikes of calcium in the oocyte
- this induces the resumption of meiosis (second polar body produced)
- cortical granules are released and these will cause cross linking of the zona pellucida to stop any other sperm from entering
Overview of Sperm entering cervix to fertilization
- Sperm swim up cervical tract to cervix
- can only get through cervical mucous after LH surge - ovulaiton, cervical mucous becomes thick and impenetrable after this
- ooctye is being ovulated, goes down fallopian tube where sperm will meet
- sperm need to undergo capacitation, hyperactivation
- partial acrosomeal reaction (due to progesterone) , burrow their way through cumulous cells and corona radiata - by hyluronidase
- penetrate zona by secreting proteases
- bind to ollengual membrane then penetrates oocyte (nueclus released)
- calcium released and it …
- activate cortical reaction - hardens zona
- also will resume meiosis 2, second polar body forms
- meiosis begins
Overview of Sperm entering cervix to fertilization
- Sperm swim up cervical tract to cervix
- can only get through cervical mucous after LH surge - ovulaiton, cervical mucous becomes thick and impenetrable after this
- ooctye is being ovulated, goes down fallopian tube where sperm will meet
- sperm need to undergo capacitation, hyperactivation
- partial acrosomeal reaction (due to progesterone) , burrow their way through cumulous cells and corona radiata - by hyluronidase
- penetrate zona by secreting proteases
- bind to ollengual membrane then penetrates oocyte (nueclus released)
- calcium released and it …
- activate cortical reaction - hardens zona
- also will resume meiosis 2, second polar body forms
- meitosis begins
Development prior to implantation + nidation
Morula
Blastocyte - start to differentaite (inner cell mass and trophectoderm –> trophoblast)
will come into contact with the endothelium and trophectoderm will adhere to the epithelium of the endometrium (via adhesion moleucels)
- (nidation)
*Reread
-Vagina pH low - seminal fluid helps buffer this so sperm dont die
-Innate immune response - to breakdown dead or dyign sperm
-capacitation - removal of inhibitory substances, sperm become hyper activated - sperm can move towards falopian tube , and enables acrosome reaciton
-acrosome reaciton - contaisn hyuranoidase and protineases - triggered by zona pelucida and progesterone - causes calciun influx into cell
-needs to cross the perivitellline space
-cotical reaction
nidation
