Fertilisation and blastocyst 1

• The female tract challenge 


  • avoid retrograde transport - stay inside the female
  • Transverse the cervix
  • Travel through the uterus
  • Travel Through the oviduct. - sticky viscous
  • Attain capacity to fertilise - freshly ejaculated sperm are not fertile must mature =
  • Capacitation , Hyperactivation and acrosome reaction.
• sperm structure 


  • acrosome - contains enzymes needed to dissolve through the zona pellucida
  • Nucleus
  • These make up the head
  • Centriole
  • Mid piece - contain mitochondrian - energy substrate
  • tail consists of
  • Flagellum inside and
  • Tail sheath - external part

  
• avoiding retrograde transport 


  • site of semen deposition affects retrograde transmission of sperm.
  • intra uterine semen deposition - pigs
  • semen squirted through cervix at copulation - horse and dog
  • maintain mating position high pressure - dog
  • viscous/ gel fraction of seminal plasma acts to plug tract - horse, pig, rodent,
  • 60% sperm lost within 12 hours in cows
  • 99% sperm lost in humans
• Variation of sperm between species 


  • starling - corkscrew shape spins
  • Human - sphere Head
  • Boar - paddle shaped - moves like boat oar
  • drosophila - long - highly coiled tail - sperm length longer than drosophila.
  • mouse - head with hook on it, mid piece and tail
• sperm with different roles - robin bakers beliefs - sperm wars book


  • fertilising sperm
  • attacking sperm - if female mated by 2 males this sperm will seek out rival male sperm to attack it - proven to be false.
• sperm co-operation

  • sperm do not attack rival ejaculates
  • instead sperm display co-operation
  • sperm from a signal male will cooperate with their own sperm to gain an advantage over rival male sperm
  • occurs in species where multiple males mate with 1 female
  • inter-male sperm competition
• Wood mouse sperm train

  • sperm head hook attached to neck region - if only 1 male sperm
  • Hook deployed in the presence of rival male sperm
  • Sperm from 1 male forms a train to increase motility.
  • Over 2mm long consisting of thousands of sperm
  • Train motility is 2x the speed of a single sperm - more likely that male will fertilise the oocyte
• Echidna sperm bundles

  • females mate approx 11 males
  • Sperm competition is rife
  • Sperm form bundles
  • 20-100 individual sperm per bundle
  • Bundles gain an advantage - faster motility
  • Number of sperm in a bundle correlates with how promiscuous the female has been
• abnormal sperm motility

  • traffic tracking system - Geoff hobson 1998
  • once computer sees sperm we can programme it to assess normality and fertility
  • computer assisted semen analysis (CASA)
  • Take slide with sperm sample on it and put under microscope and use computers to identify fertile sperm, asses quality of motility and identify abnormal motility
• Sperm head diagram

  • acrosomal sac - filled with digestive enzymes to dissolve zona pellucida
  • Plasma membrane
  • Subacrosomal space
  • Outer acrosomal membrane
  • Inner acrosomal membrane
  • nuclear envelope
  • Nucleus
  • Equational Segment - sperm docks onto egg here - where sperm egg binding occurs
  • Apical ridge - recognises zona pellucida.

  
• What allows sperm to move through female tract

  • Motility of sperm
  • viscous fluid
  • Currents caused by uterine cilia
  • Uterine contractions
  • Sperm tail -
  • Propulsive apparatus - axoneme
  • Energy production in midpiece mitochondrial sheath supplies ATP
• head abnormalities in sperm

  • nuclear vacuoles
  • tapered heads
  • ruffled acrosome
  • knobbed acrosome
• tail abnormalities in sperm

  • coiled tail
  • double midpiece
  • folded tail
  • detached head

  
• head abnormalities in sperm

  • nuclear vacuoles
  • tapered heads
  • ruffled acrosome
  • knobbed acrosome

  
• morphological abnormalities on sperm

  • reflect genetic problems
  • the less normal karyotype the more increase in structural chromosome aberrations
  • affects viability of fertilised offspring if they occur
• Does abnormal morphology matter in normal mating

  • abnormal morphology will be selected out by female reproductive tract naturally
  • As abnormal morphology affects ability to fertilise
  • Natural mating involves sperm competition
  • Natural selection and survival of the fittest
• intra cytoplasmic sperm injection (ICSI)

  • modified IVF
  • no natural selection
  • used with abnormal sperm which naturally would not make it to fertilisation
  • sperm abnormality reflects genetic problems
  • often try to pick most normal sperm unless unavailable