1. pre fertilisation sperm events Flashcards
the head of spermatozoa contains
- nucleus/DNA
- acrosomal enzymes
the middle piece of spermatozoa contains
- packed full of mitochondria for ATP generation
- microtubules
what occurs during the first stage of sperm maturation (epididymis head –> tail)
- trnasport through epidid takes 1-2 weeks
- developing spermatozoa acquire ability to be motile, fertilise and the cytoplasmic droplet moves distally
what is the role of seminal plasma in the female tract
- transport medium
- nutritional support (mainly fructose)
- buffering capacity
- antioxidants
- proteins bind to sperm head
- prostaglandins
where is semen depositied in the cow
cranial part of vagina
where is semen depositied in the sow
cervix and then immediately flushed to uterus by subsequent fractions
outline the journey of sperm through the female reproductive tract
- intermediate transport (some retrograde loss)
- crossing cervix
- transport through uterus
- uterine tube (capacitation completed, hyperactive motility)
- acrosome reaction and fertilisation
how do spermatozoa move
combined tail and head rotation
- move in straight line
- generated through head rotations
- wave movement of flagellum (coordinated head to tail, low amplitude)
- requires energy
- assisted by female reproductive tract contractions
explain how sperm are able to move their flagella
have central axoneme at core anchored to centriole
- dyneins attached to core bind to each outer doublet and xtend their motor domains onto opposing outer doublets. outer doublet slides over each other causing the axoneme to bend
list possible tail abnormalities
what is the purpose of the cervix in terms of copulation
- protection against pathogens
how does the cervix permit sperm to pass but not pathogens
secretions of 2 different types of mucus
- sialomucin = low viscosity
- sulphomucin = high viscosity
sperm pass through low viscosity areas but non-motile sperm get trapped. acts as reservoir
how do sperm get through uterus to uterine tube
how does the sperm interact with the uterine tube
- sperm bind to epithelial cells aided by seminal proteins
- renders them immobile (prolongs lifespan)
- sperm released from epithelium around ovulation (indiuced by secreted oviductal factors)\swim towards ampulla region
- due to chemotaxis/thermotaxis
- sperm become hypermobile after release
what is sperm capacitation and what does it involve
- enables sperm to be capable of fertilisation
- likely to occur in cohorts
involves:
- removal of decapacitation factors1
- membrane destablisation induced by ion movement (influx of HCO3 and Ca)
- detachment from the oviductal epithelium
- transient hyperactivity
- surface proteins exposed that can bind to oocyte
- enable acrosome reaction
- reversible
discuss sperm movement at fertilisation
hyper active movement
- flagellum move in asymmetric, high amplitude, whiplash movements (looks straight in oviductal mucus)
- lifespan is short
how does sperm bind to the oocyte
requires specific alignment
zona pellucida has 3 glycoproteins - one of which receptor (species specific) for sperm
- receptor promotes acrosome reaction
what is the acrosome reaction in sperm
- occurs after capacitation
- initiated by sperm binding to zona pellucida
- release of acrosomal hydrolytic enzymes (ZP digested, opens small localised hole)
- head then penetrates ZP (requires hyper activation of flagellum)
- plasma membranes (between oocytes and head) fused and sperm genetic material intorduced to egg
sperm binding to oocyte induces what in the oocyte
- influx of Ca ions
- complettion of meiosis 2
what is the cortical zona reaction
- oocyte contains cortical granules near to its membrane
- contents released when sperm binds
- ZP hardens
- sperm receptors are destoryed, blocking polyspermy
outline the event of perfilisation
- sperm need to undergo maturation in the epididymis
- in some species sperm will need to transverse the cervix
- there is rapid and sustained transport to uteine tube
- sperm is stored in uterine tube
- sperm need to undergo capacitation for fertilisation
- sperm bind to the oocyte via specific ZP receptor
- acrosome reaction initiated (penetrates ZP)
- the cortical reaction prevents polyspermy
- fusion of nuclei
