L06: Fertilisation Flashcards
What 2 things are required from each other sexes for fertilisation to occur
Sperm
Egg
Where does the sperm mature
In the male tract- epididymis
What does capacitation of the sperm occur
In the female tract
What meiosis is the egg after ovulation arrested at
Meiosis 2 metaphase 2
After ovulation of the egg what picks up the egg to carry it in the uterine tube
Fimbrae
What allows the egg to become picked up by the fimbrae
Follicular fluid in the oocyte that contains chemoattractants
What allows the movement of the egg within the uterine tube
Muscle contracts
What happens to the number of sperm as it moves up the female tract
Decreases
What happens to the sperm in the upper vagina
Coagulates
What cause the sperm to coagulate in the upper vagina
Semenogelin
What causes the breakage of semenogelin afterwards to allow the sperm to flow out
PSA (prostate specific antigen)
If sperm move up through the vagina where does it next enter
The cervix
When is the cervix least viscous
During 9-16 days of the cycle
What does the less viscosity of the cervix allow the sperm for
Sperm selection
What guides the sperm to the ovaries
Myometrium contraction
What junction do sperm pass to enter the uterine tube
Uterotubal junction
What happens to the viscosity in the uterine tube as the sperm moves through it
Increases
What does the increasing viscosity do
Make it harder for sperm to swim
Where does most fertilisation occur
ampulla region of uterine tube
Describe the process that occurs for the egg to penetrate the egg
1) sperm goes through the cumulus cells that are around the oocyte
2) the sperm breaks the hyaluronic acid so the cumulus goes away
3) sperm binds to the zona pellucida via 4 glycoproteins
4) sperm undergoes acrosome reaction
5) sperm goes through zona pellucida
6) sperm enters the perevitelline space (gap between zona pellucida and oocyte plasma membrane)
7) equatorial segment of sperm head fuses with oocyte plasma membrane
8) the egg engulfs the sperm nucleus to form a vesicle
9) this causes an increase in calcium that triggers the stages of development
What is izumo
A protein on the sperm membrane involved in the fusion of egg membrane
When is izumo present
After the acrosome reaction of sperm
What is Juno
The receptor for izumo
Where is Juno located
On the oocyte plasma membrane
When a vesicle forms in the egg what triggers the calcium I increase
Phospholipase c zeta
What is phospholipase c zeta
A sperm specific enzyme
What is the purpose of a calicum influx when the sperm vesicle forms in the oocyte
Release of meiosis 2 block
Why do we need to complete meiosis 2 of the egg
So the egg is haploid and combined with the sperm nucleus that is already haploid
Describe the molecules involved in the meiotic block
1) usually a m-phase promoting factor (MPF) that is made of cyclin dependent kinase + cyclin B, blocks metaphase to anaphase transition
2) MPF is also stabilised by cytostatic factor (CSF)
What happens when there is an increased calcium to remove the meiotic block
- Calcium suppresses CSF activity
- Calcium destroys Cyclin B by acitvating anaphase promoting complex (APC/C)
What other molecules apart from MPF hold the egg in meiotic arrest
Cohesion protein complex
How does the cohesion protein complex cause arrest in meiosis
Cohesion protein complex holds the sister chromatids together and resists the pulling force of microtubules
How can the cohesion protein complex become cleaved
By an enzyme known as seperase
Why is seperase enzyme inactive before fertilisation
Securin is bound to it
After fertilisation to remove the cohesion protein complex how is seperase activated
The anaphase promoting complex ubiquitinates securin so seperase is active and cleaves the cohesion protein complex
What are the 2 ways in stopping more than 1 sperm fertilising the egg
1) fast block
2) slow block
What is fast block
When the egg membrane depolarises after the sperm has entered
What is the slow block
Zona reaction
What is the zona reaction
A change in the zona pellucida due to cortical granules that release enzymes of proteases which clear the zona pellucida receptors on the egg
What happens to Juno (egg membrane receptor)
Becomes shed with the cortical granules so sperm cannot fuse
When the sperm and egg fertilise, what does the sperm bring
Haploid male genome
Centriole
What does the haploid male genome determine
The sex of the baby
What does the centriole allow
Spindle formation for first cell division
What does the egg bring in fertilisation
Haploid female genome
Cytoplasma
All organelles
Mitochondria
What has to happen to the sperm dna for it to get together with the female genetic material in the zygotic stage
DNA has to decondense
Why does the male dna decondense in the zygotic stage
Because the dna is highly packed in the sperm
After the sperm DNA has decondensed what happens to the male and female pronuclie
Replicate their dna
How does the male and female pronuclie fuse
They migrate towards eachother
What is the migration of the male and female pro nucleus guided by
Sperm aster ( a group microtubules radiating from the sperm centrosome)
What occurs in syngamy
1) Pronuclear membranes break down
2) chromatin from both pronuclei intermixes on a spindle structure
3) nucleus involve reforms around zygote nucleus
4) cleavage (division) begins- marks end of fertilisation/begging of emrbyogenis
Where does the embryo have to go to become implanted
Uterus
What allows the transport of the embryo to the uterus
High level of progesterone
Cilia
What does high levels of progesterone do to the muscles
Relax the muscles so the embryo can pass through tight junctions such as the isthmic spinchter
What does cilia do
Move the uterus along the uterine tube to the uterus
What is cleavage
The division of the zygote
When does cleavage occur
As the embryo is travelling down to the uterus
State the stages the zygote goes through in cleave
Zygote 2 blastomeres 4 cell stage 8 cell stage Morula (16-32 cells) ( at the end of the uterine tube)
What controls the development up to the 2 cell stage
Oocyte cytoplasm
What controls the development up to the 4 to 8 cell stage
Activation of genome to produce own proteins
After the 8 cell stage what do we enter
Compaction
What happens in compaction
Embryo becomes tightly compacted
What forms before we get to the blastocyst stage
Trophoblast (outer layer) goes to from the placenta
Inner cell mass (inner cell) goes to form the embryoblast
Formation of fluid filled cavity called blastocoel
When does blastocyst formation occur
After day 5 of fertilisation
What hormone is produce at the blastocyst
HCG
Which structures give HCG
Blastocoele
Trophoblast cells
What happens after day 6
Hatching
What does the hatching involve
1) Blastocyst expands the the zona pellucida through the abembroyonic pole
2) This allows embryo to squeeze out and blastocyst with trophoblast layer implants
What are the 2 types of twins that we can have
Monozygotic
Dizygotic
What increases the risk of dizygotic twins
Increased maternal age
IVF treatment
What increases the risk of monozygotic twins
In vitro embryo culture
What are the 4 types of monozygotic twins that we can get
Dichorinoic/diamniotic
Monochorionic/ diamnioatic
Monochorionic/ mono amniotic
Conjoined twins
What is dichorionic/ diamniotic monozygotic twins
Twins that have own placenta and own amniotic sac
What is monochorionic/diamniotic monozygotic twins
Twins that share own placenta and own amniotic sac
What is monochorionic/mono amniotic
Twins that share own placenta and amniotic sac
What is conjoined twins
Twins that are joined together
What is the risk of monochorionic (same placenta)
Unequal blood flow
What is the risk for monoamniotic (same aminotic sac)
Umbilical cord becoming tangled and compressed
What are the 2 muscle layers of the uterus
Endometrium
Myometrium
How many layers does the endometrium have
2
What are the 2 layers of the endometrium
Upper functional layer
Low basal layer
What does the upper functional layer do
Proliferate every month to give menstruation
What is the basal layer of the endometrium attached to
Myometrium
What are the cell types in the endometrium
Stromal matrix cells that contain spinal arteries
Luminal epithelial cells that line the stromal matrix
What occurs in the proliferative/ follicular phase to the cells of the endometrial
The cells proliferate due to an increased oestrogen
Thickening of stromal cells
Increase of surface epithelium
Glandular invagination increase
After ovulation what hormone is expressed
Progesterone
What does progesterone stimulate in the secretory/ luteal phase
Secretion by glands that are in rich of glycogen, glycoproteins and amino acids for the nutrition to blastocyst
What happens to the cells in the secretory/luteal phase
Stromal cell become larger
Spinal arteries fully develop
At the end of the secretory/luteal phase what type of endometrium do we have
Receptive endometrium
What does a receptive endometrium mean
Endometrium that is ready for implanting
How many days does the window for implantation last for
4 days
What is the window for implantation characterised by
Pinopodes
What are pinopodes in the endometrium involved in
Absorption of the uterine fluid
What does the absorption of the uterine fluid allow
Bringing the blastocyst blaster to the endometrium and immobilise it
If there is no blastocyst what happens to the endometrium
Spiral artery constrict
Functional layer collapse and necrosis
To allow menstruation what hormone level cause it
Decrease in progesterone
