Pre-fertilisation sperm events Flashcards
Sperm consists of what three main parts?
Head- nucleus/DNA and the acrosome enzymes
Middle piece – packed full of mitochondrion, ATP generation and microtubules
Tail (Flagellum) – propels the sperm at 3mm/min
How long does sperm maturation take?
2-3 weeks
After maturation the sperm are mixed with seminal plasma, what does this provide for the sperm?
Transport medium
Nutritional support (contains fructose- the sperm energy source)
Buffering capacity
Antioxidants (ascorbic acid)- helps with the rapid metabolism
Prostaglandins – from the prostate which causes female contraction
Proteins to protect the sperm head
In the horse and dog it is deposited in the cranial vaginal however……..
……because the cervix is open it immediately flows into the uterus
After deposition, semen are lost because of….
Retrograde transport (which can be prevented by coagulation) and after a period of time these will be phagocytised and there will be neutrophil infiltration
How do sperm move when activated?
When the sperm are activated they move in a straight line with head rotations and a wave movement of the flagellum (low amplitude neck to tail movement)
What does the flagellum consist of?
The flagellum consists of a central axoneme, anchored in the centriole it consists of 9 (symmetrical) pairs of outer microtubules, and Dynein’s which are bound to each outer doublet and extend their motor domains toward adjacent doublet (this allows the doublets to slide over each other and bend the axoneme)
Name some common sperm abnormalities
Coiled tail
Double mid piece
Folded tail
Detached head
What are the two types of mucus produced in the cervix?
Sialomucin (low viscosity) and Sulphmucin (high viscosity)
What is the purpose of cervical mucus?
The function of this is to create a spermatozoa reservoir in the crypts and remove non-motile sperm (only vigorous sperm succeeds) and functions to create a steady stream of sperm through the uterus rather than a large rush.
As sperm move through the uterus what is the effect on endocrinolgy?
As sperm moves through the uterus to the oviduct oestradiol, oxytocin and prostaglandins (from semen) increase tone and motility of the female tract
Before reaching the oviduct what structure must sperm pass through?
The sperm is then funnelled through the uterine-oviductal junction, this requires vigorous sperm motility and might close after a certain point in time.
What is the uterine sperm reservoir in dogs?
The first fraction of ejaculate is prostaglandin rich, the second sperm rich and the last forms the coagulation. The sperm will then bind to the epithelial lining of the uttering horns (uterine sperm reservoir) which allows them to remain functional for longer and reduce polyspermy (one egg is fertilised by more than one sperm)
What will sperm do when they reach the oviduct?
Normally only around 10% of sperm reach the oviduct, when they reach there they bind to the oviductal cells and become immotile, this prolongs their lifespan. The sperm are then released around ovulation (due to oestradiol being secreted) they then swim towards the ampulla (latter part of the oviduct), the egg sends thermotaxis and chemotaxis to help direct the sperm. This is also the main site of capacitation which is induced by heparin and assists in the release of the sperm.
Do all sperm undergo capacitation at the same time?
It tends to occur in waves
Describe the events in capacitation
Involves the removal of decapacitation factors, membrane destabilation due to ion movement (notably influx of HCO3- and Ca2+).
The sperm then detach from the oviductal epithelium and experience transient hyperactivity, which involves exposure of surface proteins that can bind to the oocyte (ZP proteins) and is the precursor to the acrosome reaction.
After capacitation what is the lifespan of the sperm?
After this time the sperm has a short lifespan of only 5-6h in cows or 2-3h in pigs (however this is reversible in vitro)
What happens to the sperm after capacitation, how does this aid them?
Once capacitation has occurred the sperm experience hyperactivated movement where the flagellum moves asymmetrically with high amplitude in a straight line (in oviductal mucus, however circular in vitro). This aids sperm penetration of the egg.
What is the function of the zona pellucida and the cumulus cells?
The glycoprotein band called the zona pellucida functions to protect the fertilised egg and the cumulus cells add an extra barrier for the sperm
What is the zona pellucida made up of?
The zona pellucida is made up of three glycoproteins:
ZP1- minor component
ZP2- structural component
ZP3- is the species-specific receptor, which will recognise the primary zona binding region (ZBR) and acrosome reaction promoting region (ARPR) on the sperm.
When does the acrosome reaction occur?
The acrosome reaction occurs after capacitation, it is initiated by sperm binding to the ZP
What is the acrosome reaction?
The sperm head triggers the release of acrosomal hydrolytic enzymes (Acrosin) which creates a small hole in the ZP which is then sealed up afterwards
What triggers the completion of meiosis II in the oocyte?
sperm binding to the oocyte induces an influx of Ca2+ and completion of meiosis II.
The binding of the sperm also initiates the cortical reaction, what does this consist of?
The ZP hardens and the sperm receptors are destroyed, this is the major block to polyspermy.
