Fertilization Impantation Flashcards
What are the three layers that the sperm has to penetrate to fertilize the egg?
Outermost layer = Cumulus Cell matrix (corona radiate)
middle = Zona Pellucida
innermost = Plasma membrane (Oolemma)
Fertilization occurs at what day?
what does fertilization allow for?
Day 15 or 16.
allows for recombination of genetic material
initiation of events before embryonic development
fertilization happens mostly where?
sperm and egg travel where once fertilization happen?
ampulla of the uterine tube.
fundus of the uterine cavity.
What are the 2 steps of fertilization?
capacitation (step 1)
Acrosome reaction (step 2)
Why does capacitation need to happen?
in the male genitalia track there’s a high level of cholesterol which hardens and inhibits the acrosome from using its proteolytic enzymes so it keeps the sperms at bay, not allowing the sperm to be activated.
Once the sperm enters the female genital tract, what does the uterus do?
2 things
what does the effect of calcium have on the sperm? (2) things
uterine and Fallopian tube fluids wash away inhibitory factors (cholesterol) on the sperm
the acrosome membrane that was hardened will now be permeable to calcium –> this calcium allows the tail to move faster and make it faster… also activates the sperm to release its enzymes
What is the acrosome reaction?
the release of the enzymes in the acrosome to break through the 3 layers of the ovum to release its DNA inside
What is the outermost layer of the egg and what breaks it down?
cumulus cell matrix
made up of hyaluronic acid.
What is the second layer of the egg? what is it made of?
Zona Pellucida
ZP1, 2, and 3
ZP1 is structural.. it cross links ZP2 and 3
ZP2 –> blocks polyspermy
ZP3 initiates acrosome reaction.
After capacitation, what receptor does the sperm now have?
no capacitation?
what does it use this for?
ZP3
no ZP3
it needs it to break through the second layer.
it uses the receptor to bind to ZP3.. once its bound, it allows the sperm to release all its enzymes which break apart the zona pellucida.
What happens to the sperm once it gets through the zona pellucida?
then what happens?
it loses its ZP3 receptor
it now can bind to ZP2
Once the sperm binds to ZP2, what happens?
the ovum recognizes this and says “hey, one of the sperm got through, so we can’t let any more enter”
so the binding of ZP2 (from the released ZP3) is what causes the Egg to not allow any more sperm to enter
once the first sperm hits the plasma membrane, what happens?
it just goes through, and it’ll release its DNA so it can be bound to the female ovum’s DNA
During the times of the month when the reproductive tract Is not releasing the egg, what is the female reproductive tract trying to do?
the female reproductive tract is trying to get pregnant.
if it knows its not the time of the month, its going to allow the body to hold onto sperm in a “sperm” reservoir, which is located in the oviductal isthmus..
sperm just hang out and bind to the epithelium. It’s not activated until the right time.
after fertilization, what’s the first reaction to happen?
Cortical reaction
what is the cortical reaction?
when the egg releases granules and calcium to prevent polyspermy.
ZP2 is going to bind to the released ZP3.. this is going to change ZP2 to ZPF.
that hardens the entire zona pellucida which prevents any sperm from entering the egg.
What does the release of calcium during the cortical reaction do?
the egg is now active. what does it do then?
stimulate the egg to go through meiosis 2
the egg is finally activated and the sperm DNA can condense and there will be fusion of the male and female pronuclei to result in the first embryonic cleavage or the result of a Zygote.
The first week of embryonic development.. what are the 2 stages?
1: compaction and blastocele development
2: blastocyst hatching
compaction?
occurs with the morula which is around day 3.
the morula is a 16 cell mass
(day 4) –> what happens is the outer cells of the morula is going to increase cell to cell adhesions via tight junctions and desmosomes to really bring the cells together.
what it results in is an outer layer of trophoblasts which ends up making the extra embryonic structures (placenta) and it results in an inner cell mass which will end up being the embryo proper (or the actual embryo)
while it compacts and forms the two distinct structures what else does it increase?
sodium and osmosis to form the blastocele
embryo proper is what?
what about the morula?
pluripotent.. so it has the potential to be endoderm, mesoderm, or ectoderm
morula are totipotent
Day 5 is what?
what happens?
late blastocyst –> hatching!
the entire structure will hatch from the zona pellucida.
recall that the zona pellucida was hardened during the cortical reaction
that hardened zona pellucida is still enveloping the blastocyst and that is a problem because if you have a hard envelope around the blastocyst that means that the embryo is trying to grow, but it can’t do so as it’s being restricted.
so it needs to hatch or leave in order to grow and develop
If you have someone who is unable to hatch the blastocyst from the zona pellucida then what happens?
infertility. the embryo can’t grow and develop