Fertilisation and Blastocyst Development Flashcards
sperm motility and morphology
What is the basic journey of the sperm?
- avoid retrograde transport - falling back out
- transverses the cervix
- travel through the uterus
- travel through the oviduct
- attain the capacity to fertilise
What are the 3 basic steps sperm need to undergo to attain the capacity to fertilise?
- capacitation
- hyperactivation
- acrosome reaction
What percentage of sperm are lost within 12 hours in the cow?
- 60%
How do pigs deposit semen?
- intra uterine semen deposition
- intra corkscrew penis
How do the horse and dog deposit semen?
- semen squirted through cervix at copulation
What do dogs do after mating?
- maintain mating position, high pressure (dog) tie so they cannot be separated (bum to bum)
What plugs the tract in horses, pigs and rodents?
- viscous/gel fraction of seminal plasma acts to plug the tract
Sperm first enters through the cervix to get to the uterus - what happens here?
- there is removal of abnormal sperm as if there isn’t good sperm motility they wont get through
What does the uterotubal junction do?
- selects sperm due to surface proteins
What is initiated in the uterus?
- capacitation initiated
What happens in the oviduct?
- capacitation is completed
- hyperactive motility
What happens during fertilisation?
- acrosome reaction
- sperm penetrates oocyte
What helps sperm to move through the female tract?
- motility of the sperm itself
- viscous fluid currents caused by uterine cilia acts to propel sperm along
- uterine contractions to aid motility towards the oocyte
The sperm tail has two comments that aid in motility what are these?
- midpiece mitochondrial sheath which supplies ATP = energy production
- propulsive apparatus which is the axoneme
How does the tail of the sperm move?
- only whips in one direction
- head and tail work in different directions so the sperm doesn’t move in circles
What can we use to evaluate sperm motility?
- computer assisted semen analysis
= CASA
What does mouse sperm have?
- the head of the sperm has a hook
Why does mouse sperm have a hook?
- sperm can attack other species sperm to reduce other males from fertilising the female
- can have fertilisation function = sperm trains = co-operation to again advantage over other males sperm
When are sperm hooks deployed?
- only deployed when foreign sperm is detected
Sperm hooks are deployed in the presence of rival males sperm - they can form sperm trains what do these do and what are they like?
- sperm forms trains to increase motility
- over 2mm long consisting of thousands of sperm
- train fertility is twice the speed of individual sperm
Female echidna can mate up to 11 times - what does competition sperm form?
- sperm form bundles
What are sperm bundles and what do they do?
- 20-100 individual sperm per bundle
- bundles gain an advantage
- number of sperm in a bundle correlates with promiscuity of the female
What head abnormalities can sperm have?
- nuclear vacuoles
- tapered heads
- ruffled acrosome
- knobbed acrosome
What tail abnormalities can sperm have?
- coiled tail
- double midpiece
- folded tail
- detached head
What can morphological abnormalities reflect?
- reflect genetic problems
How are abnormal morphologies selected out?
- selected out by the female reproductive tract = cervix anatomy
What does abnormal morphology affect?
- affects ability to fertilise
What does natural mating involve (for sperm)?
- sperm coemption
- natural selection and survival of the fittest
What does ICSI stand for?
- intra cytoplasmic sperm injection
What is ICSI and what does it involve?
- modified IVF
- no natural selection
- used with abnormal sperm
- however sperm abnormalities reflects genetic issues!
Sperm movement has 2 phases - what are they?
- rapid transport phase
- sustained transport phase
What happens in the rapid transport phase?
- sperm reaches oviduct within minutes
- unable to fertilise the oocyst until second phase
What happens during the sustained transport phase?
- capacitation
- hyperactivation
- acrosome reaction
Ejaculated sperm cannot fertilise the oocyst. Sperm must undergo capacitation - what is this?
- progressive destabilisation of the plasma membrane
- female tract strips some proteins leaving exposed areas for sperm-egg binding
What is the process of capacitation?
- glucoprotein molecules coating sperm head removed
- exposure of zona pellucida binding proteins
- allows sperm to bind to the oocyte at fertilisation
- surface charge altered - may attract sperm to oocyte
- membrane fluidity increased to aid breakdown of acrosome
Capacitation - what happens in the epididymis?
- surface molecules added
= proteins and carbs
Capacitation - what do sperm look like at ejaculation?
- surface molecules coated with seminal plasma proteins
= decapacitation factors
Capacitated sperm then exhibit what?
- exhibit hyperactivated motility
What happens during hyperactivation?
- strong, wide amplitude, whiplashing tail beats
- increased intracellular calcium leads to elevated cAMP
- increased force required to swim through viscous environment within the oviduct
In vitro hyperactivation leads to what?
- more head movement and less linearity
Capacitation exposes zona pellucida binding proteins on the sperm plasma membrane. Sperm then binds to the zona pellucida - what initiates the sperm acrosomal reaction?
- binding
What does the acrosome reaction do?
- fusion of the sperm plasma membrane and outer acrosomal membrane
- release of enzymes to digest the zona pellucida
- exposure of equatorial segment for oocyte fusion
What does the sperm look like before the acrosome reaction?
- all membranes are intact
What does sperm look like during the acrosome reaction?
- plasma membrane fuses with the outer acrosomal membrane
- fusion causes vesiculation producing pores
- release of hyaluronidase and acrosin
What does the sperm look like after the acrosome reaction?
- vesicles lost
- inner acrosomal membrane and equatorial segment exposed
What digests small holes in the zonal pellucida?
- acrosomal enzymes
How fast is the penetration of the zona pellucida?
- rapid process
Where do sperm move once they start to digest the zona pellucida?
- sperm move into perivitelline space between zona and oocyte plasma membrane
Gametes have how many copies of chromosomes?
- haploid (1n)
- haploid cells have single copies of each chromosome
At fertilisation what nucleus does the oocyte have?
- female pronucleus (1n)
What nucleus does the sperm contribute?
- male pronucleus
What happens to the nucleus’ following fertilisation?
- the male and female pronuclei fuse to produce a diploid (2n) zygote
After the zygote is formed what does it undergo?
- undergoes miotic cleavage
What does the first miotic cleavage division create?
- a two-cell embryo
Cleavage goes on to form what?
- 4, 8, 16 cell embryo
Each cell in the early embryo is called what?
- blastomere (undifferentiated)
What is each blastomere like?
- genetically identical
2 distinct layers form to create the blastocyst - what are there layers?
- inner ball of cells (inner cell mass)
- cells at the periphery (trophoblast)
What doe the cell in the outer mass do? (blastocyst)
- pump sodium into the blastocyst creating accumulation of fluid, blastocoele
What does the inner cell mass of the blastocyst become?
- the embryo proper
What do trophoblast cell become?
- the placenta
Where does the blastocyst move?
- moves down the oviduct towards the uterus
Implantation of the blastocyst is prevented by what?
- the zona pellucida
At the uterus the blastocyst hatches how and what does it become?
- hatches by digesting a hole in the zona pellucida
- blastocyst becomes a free-floating embryo
- now dependent on the uterus for survival
