Prefertilisation sperm events Flashcards
Where is sperm deposited in the ewe?
Vagina
Where is sperm deposited in the cow?
Vagina
Where is sperm deposited in the mare?
Uterus
- Initially deposited in cranial vaginally but will flow through open cervix to uterus
Where is sperm deposited in the sow?
Cervix/uterus
- Corkscrew penis and counter-corkscrew cervix, engage during copulation, long tract
Where is sperm deposited in camelids?
Uterine/cervix/vagina
Where is sperm deposited in the bitch?
Vagina (a lot will end up in uterus due to open cervix)
Describe structure and function of the head of spermatozoa
- Contains nucleus/DNA
- Acrosomal enzymes
Describe structure and function of the middle piece of spermatozoa
- Full of mitochondria
- ATP generation
- Microtubules
Describe the structure and function of tail of spermatozoa
- Propels sperm/movement
- 3mm minimum
- Allows for directional movement
What features develop as part of the maturation process in the epididymis?
Develop the ability to be motile
- The ability to fertilise
- cytoplasmic droplets
What features are acquired in the head of the epididymis?
The ability to move and fertilise
Where does the cytoplasmic droplet develop?
Throughout the migration of the sperm through the epididymis
Explain the importance of the epididymal tail
- Can store a large number of spermatozoa
- Allows more frequent ejaculation
How do sperm move?
- rotation of head
- Tail moving in wave like motion top to bottom
- Low amplitude initially
Describe the structure of the flagella of sperm
- Dentral axoneme with dyneins running length of flagellum
- Outer dense fibres surrounding axoneme in midpiece and central piece
- Fibrous sheath in principle piece
- Mitochondrial sheath in midpiece
Describe the structure of the central axoneme
- Anchored in centriole
- has pair of central microtubules
- Outer ring of 9 pairs of outer microtubules (symmetrical)
- Dyneins bound to each outer doublet
Explain how the dyneins work to make the flagellum move following ejaculation
- Bind to each outer double
- Extend motor domains towards adjacent outer doublet
- Outer doublets slide over each other
- Leads to bending of axoneme
Describe hyperactivated movement of spermatozoa
- Moves asymmetrically, high amplitude, straight in oviductal mucus, whiplash
- Facilitates sperm-oocyte contact
- Go in circles
When does hyperactivated movement of the sperm occur?
After capacitation
What is the function of the seminal plasma?
- Not essential for fertilisation
- Aids transport of sperm through urethra of male and then female tract
How does seminal plasma carry out its function?
- Nutritional support (fructose, glucose in horse)
- Buffering capacity
- Antioxidants (ascorbic acid)
- Prostaglandins
What is the function of the prostaglandins in the seminal plasma?
- Stimulates muscuar activity in female tract
- May help move sperm towards uterus
- Cervix may filter out some PGs
Give an overview of the journey taken by the spermatozoa following copulation
- Immediate transport
- Cervix
- Tansport through uterus
- Oviduct
- Fertilisation
How can spermatozoa be lost following copulation?
- Retrograde transport
- Phagocytosis after period of time
- Loss through vagina and vulva
- Once sperm enters uterus, recognised as foreign so induces immune response
- Neutrophil infiltration into uterus following insemination rapid
Describe the function of the secretion of mucus within the cervix following insemination
- Sialomucin (low viscosity) and sulphomucin (high viscosity)
- Creates spermatozoa reservoir and removes non-motile sperm
- Only vigorous sperm can utilise the privileged pathways
- Non-motile sperm are likely to get stuck meaning they can be removed
- Acts as reservoir as sperm stick to lining and are tehn released over time = sustained flow of sperm to uterus
Describe the transport of sperm through the uterus to the oviduct
- Rapid transport minutes after copulation
- Likely to be in oviduct before egg, fertilisation unlikely
- Sustained release from cervix means more likley to fertilise
- Elevated tone and motility of mscularis of female tract
What stimulates the increased tone and motility of the muscularis of the female tract following copulation?
- Oestradiol
- Oxytocin
- PGs from seminal fluid
Describe the uterine sperm reservoir found in dogs
- 2nd fraction of ejaculate is sperm rich fraction
- At tips of uterine horns, sperm bind to epithelial cells in sperm reservoir
- Aided by seminal proteins
- Reduces polyspermy
- Sperm remain function for many days
- Is the main site of capacitation
Describe the release of sperm from the reservoir in the oviduct
- Released around ovulation swim towards ampulla region
- Thought to be due to chemotaxis/thermotaxis
- Release triggered by secretion of oviductal factors under influence of hormones e.g. oestradiol
Describe the sperm and oocyte meeting
- Sperm released from oviductal lining around ovulation
- Swim through isthmus and into ampulla
- Met in the ampulla
What is capacitation?
The second stage of sperm maturation, renders sperm able to fertilise
Where does capacitation occur?
In the oviduct, likely as cohorts
What are the 4 steps involved in capacitation?
- Removal of decapacitation factors
- Membrane destabilisation
- Detachment from the oviductal epithelium
- Transient hyperactivity
How does membrane destabilisation in capacitation occur?
- Ion movement
- Influx of HCO3-/Ca2+
Describe the removal of decapacitation factors
- Sperm has proteins on head at end of epididymis
- Add seminal plasma so more proteins bind
- at correct time, all of these will be removed, exposing head of sperm and allowing fertilisation
Describe the transient hyperactivity of sperm
- Due to exposure of surface proteins that bind to oocyte (ZP proteins)
- Enables acrosome reaction to take place
- Short life span
Describe the structure of the oocyte
- Central ooplasm (egg itself)
- Surrounding that is glycoprotein band = zona pellucida
- Surrounding that are cumulus cells
Describe the components of the zona pellucida
- 3 glycoproteins
- ZP1: minor component
- ZP2: structural component
- ZP3: receptor
Describe the ZP3 receptor
- Species specific
- Recognises proteins of sperm
- Primary zona binding region (ZBR)
- Acrosome reaction promoting region (ARPR)
What prevents the sperm of one species binding to the egg of another?
The specificity of the ZP3 receptors
When does the acrosome reactions take place?
- After capacitation
- Initiated by sperm binding to the ZP
Describe the acrosome reaction
- Release of acrosomal hydrolytic enzymes
- Digestion of ZP (acrosin)
- Localised small hole
- Sperm migrates through (requires hyperactivation of flagellum)
- Fusion of plasma membranes takes place
What are the steps in oocyte activation?
- Ovulation inducing completion of meiosis I in oocyte
- Sperm binding to oocyte
- cortical/zona reaction
- Membranes fuse to start fertilisation
What is induced by the sperm binding to the oocyte?
- Influx of Ca2+ ions
- Completion of meiossi II
- Cortical reaction
Describe the cortical/zona reaction
- Zona pellucida hardens
- Sperm receptros (ZP3) destroyed
- Major block of polyspermy
