Pre-fertilisation sperm events Flashcards
What is the structure of a spermatozoon?
Head:
- nucleus/DNA
- acrosome (enzymes)
Middle piece:
- packed full of mitochondrion
- ATP generation
- microtubules
Tail/flagellum:
- propels sperm
Where does the first stage of sperm maturation take place?
Epididymis
Explain the transportation and maturation of sperm in the epididymis
Transport takes 1-2 weeks
Acquire ability to be motile
Acquire ability to fertilise
Cytoplasmic droplet moves distally
Label the testis
What is the role of seminal plasma for sperm in the female tract?
Transport medium
Nutritional support
Buffering capacity - cervix tends to be acidic
Antioxidants
Proteins bind to sperm head
Prostaglandins cause female tract muscles to contract to aid movement of sperm
Where is sperm deposited in cattle?
Cranial aspect of vagina
Where is sperm deposited in the pig?
In uterus/cervix due to coiled penis and cervix
What process prevents sperm from being lost after copulation
Semen coagulation - prevents further mating and retrograde transport, forms plug in rodents
How is sperm lost after copulation?
Retrograde transport
Phagoctyosed after period of time (immune response to foreign body)
How does sperm move in ejaculation?
Describe the structure of the flagella of sperm
How do dyneins cause movement of flagella in sperm?
What types of sperm
tail abnormality are there?
How does the cervix act as a barrier to sperm?
Mucous secretion:
- sialomucin (low viscocity)
- sulphomucin (high viscocity)
Removes non-motile sperm as vigorous sperm are required
Describe the transport of sperm through the uterus to the uterine tube
Must pass through uterine-tubal junction
Rapid sperm transport:
- minutes after copulation
-due to elevated tone and motility of muscular layers of female tract due to elevated oestradiol and oxtocin, and due to prostaglandins in seminal fluid
Sustained sperm transport:
- in the hours after copulation
- these sperm fertilise the egg
Describe the anatomy of the uterine-tubal junction
Tortuous and narrow lumen
Funnel
Requires vigorous sperm motility
Might close after period of time
Describe the interactions of sperm in the uterine tube
Sperm bind to epithelial cells in the isthmus:
- aided by seminal proteins
- renders them immobile
- prolongs their lifespan
Sperm released around ovulation
What is special about canine ejaculation?
How does the canine uterus prevent polyspermy?
Sperm reservoirs in tips of uterine horns
Sperm binds to epithelial cells
What is polyspermy?
multiple sperm fertilising a single egg -> wrong number of chromosomes
Describe the process of sperm capacitation (2nd stage of maturation)
Enables sperm to be capable of fertilisation
- removal of decapacitation factors
- membrane destabilisation induced by ion movement
- detachment from the oviductal epithelium
- transient hyperactivity (exposure of surface proteins that can bind to oocyte, enables acrosome reaction)
Describe sperm movement in fertilisation
Hyper-activated movement:
- asymmetric
- high amplitude
- straight in oviductal mucus
- whiplash
Label this cumulus-oocyte complex
Describe the process of sperm binding to the oocyte
- specific alignment of sperm and oocyte
- sperm binds to zona pellucida after crossing cumulus cells
- release of acrosomal hydrolytic enzymes
- enzymes digest ZP and form a localised small hole
- nucleus of sperm is release into oocyte
What part of the oocyte prevents cross species reproduction?
The zona pellucida contains 3 glycoproteins (ZP 1, 2 and 3)
ZP3 - species specific through zona binding region
What occurs to the oocyte after the sperm has bound to it?
Induces influx of Ca2+ ions and completion of meiosis II
Cortical (zona) reaction:
- contents of cortical granules released
- ZP hardens
- sperm receptors destroyed
- prevents polyspermy
