Fertilisation and Blastocyst Development Flashcards
sperm motility and morphology
1
Q
What is the basic journey of the sperm?
A
- avoid retrograde transport - falling back out
- transverses the cervix
- travel through the uterus
- travel through the oviduct
- attain the capacity to fertilise
2
Q
What are the 3 basic steps sperm need to undergo to attain the capacity to fertilise?
A
- capacitation
- hyperactivation
- acrosome reaction
3
Q
What percentage of sperm are lost within 12 hours in the cow?
A
- 60%
4
Q
How do pigs deposit semen?
A
- intra uterine semen deposition
- intra corkscrew penis
5
Q
How do the horse and dog deposit semen?
A
- semen squirted through cervix at copulation
6
Q
What do dogs do after mating?
A
- maintain mating position, high pressure (dog) tie so they cannot be separated (bum to bum)
7
Q
What plugs the tract in horses, pigs and rodents?
A
- viscous/gel fraction of seminal plasma acts to plug the tract
8
Q
Sperm first enters through the cervix to get to the uterus - what happens here?
A
- there is removal of abnormal sperm as if there isn’t good sperm motility they wont get through
9
Q
What does the uterotubal junction do?
A
- selects sperm due to surface proteins
10
Q
What is initiated in the uterus?
A
- capacitation initiated
11
Q
What happens in the oviduct?
A
- capacitation is completed
- hyperactive motility
12
Q
What happens during fertilisation?
A
- acrosome reaction
- sperm penetrates oocyte
13
Q
What helps sperm to move through the female tract?
A
- 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
14
Q
The sperm tail has two comments that aid in motility what are these?
A
- midpiece mitochondrial sheath which supplies ATP = energy production
- propulsive apparatus which is the axoneme
15
Q
How does the tail of the sperm move?
A
- only whips in one direction
- head and tail work in different directions so the sperm doesn’t move in circles
16
Q
What can we use to evaluate sperm motility?
A
- computer assisted semen analysis
= CASA
17
Q
What does mouse sperm have?
A
- the head of the sperm has a hook
18
Q
Why does mouse sperm have a hook?
A
- 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
19
Q
When are sperm hooks deployed?
A
- only deployed when foreign sperm is detected
20
Q
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?
A
- sperm forms trains to increase motility
- over 2mm long consisting of thousands of sperm
- train fertility is twice the speed of individual sperm
21
Q
Female echidna can mate up to 11 times - what does competition sperm form?
A
- sperm form bundles
22
Q
What are sperm bundles and what do they do?
A
- 20-100 individual sperm per bundle
- bundles gain an advantage
- number of sperm in a bundle correlates with promiscuity of the female
23
Q
What head abnormalities can sperm have?
A
- nuclear vacuoles
- tapered heads
- ruffled acrosome
- knobbed acrosome
24
Q
What tail abnormalities can sperm have?
A
- coiled tail
- double midpiece
- folded tail
- detached head
25
What can morphological abnormalities reflect?
- reflect genetic problems
26
How are abnormal morphologies selected out?
- selected out by the female reproductive tract = cervix anatomy
27
What does abnormal morphology affect?
- affects ability to fertilise
28
What does natural mating involve (for sperm)?
- sperm coemption
- natural selection and survival of the fittest
29
What does ICSI stand for?
- intra cytoplasmic sperm injection
30
What is ICSI and what does it involve?
- modified IVF
- no natural selection
- used with abnormal sperm
- however sperm abnormalities reflects genetic issues!
31
Sperm movement has 2 phases - what are they?
- rapid transport phase
- sustained transport phase
32
What happens in the rapid transport phase?
- sperm reaches oviduct within minutes
- unable to fertilise the oocyst until second phase
33
What happens during the sustained transport phase?
- capacitation
- hyperactivation
- acrosome reaction
34
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
35
What is the process of capacitation?
1. glucoprotein molecules coating sperm head removed
2. exposure of zona pellucida binding proteins
3. allows sperm to bind to the oocyte at fertilisation
4. surface charge altered - may attract sperm to oocyte
5. membrane fluidity increased to aid breakdown of acrosome
36
Capacitation - what happens in the epididymis?
- surface molecules added
= proteins and carbs
37
Capacitation - what do sperm look like at ejaculation?
- surface molecules coated with seminal plasma proteins
= decapacitation factors
38
Capacitated sperm then exhibit what?
- exhibit hyperactivated motility
39
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
40
In vitro hyperactivation leads to what?
- more head movement and less linearity
41
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
42
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
43
What does the sperm look like before the acrosome reaction?
- all membranes are intact
44
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
45
What does the sperm look like after the acrosome reaction?
- vesicles lost
- inner acrosomal membrane and equatorial segment exposed
46
What digests small holes in the zonal pellucida?
- acrosomal enzymes
47
How fast is the penetration of the zona pellucida?
- rapid process
48
Where do sperm move once they start to digest the zona pellucida?
- sperm move into perivitelline space between zona and oocyte plasma membrane
49
Gametes have how many copies of chromosomes?
- haploid (1n)
- haploid cells have single copies of each chromosome
50
At fertilisation what nucleus does the oocyte have?
- female pronucleus (1n)
51
What nucleus does the sperm contribute?
- male pronucleus
52
What happens to the nucleus' following fertilisation?
- the male and female pronuclei fuse to produce a diploid (2n) zygote
53
After the zygote is formed what does it undergo?
- undergoes miotic cleavage
54
What does the first miotic cleavage division create?
- a two-cell embryo
55
Cleavage goes on to form what?
- 4, 8, 16 cell embryo
56
Each cell in the early embryo is called what?
- blastomere (undifferentiated)
57
What is each blastomere like?
- genetically identical
58
2 distinct layers form to create the blastocyst - what are there layers?
- inner ball of cells (inner cell mass)
- cells at the periphery (trophoblast)
59
What doe the cell in the outer mass do? (blastocyst)
- pump sodium into the blastocyst creating accumulation of fluid, blastocoele
60
What does the inner cell mass of the blastocyst become?
- the embryo proper
61
What do trophoblast cell become?
- the placenta
62
Where does the blastocyst move?
- moves down the oviduct towards the uterus
63
Implantation of the blastocyst is prevented by what?
- the zona pellucida
64
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
