Fertilisation in humans

• How long can sperm survive in the female reproductive tract?

  1-2 days
• What happens as sperm moves through the female reproductive tract?

  The acrosome of the sperm matures so that it is able to release enzymes to penetrate the ovum
• What stage of oogenesis is the ovum released as part of ovulation at?

  Secondary oocyte (with one polar body)
• What happens when a sperm head touches the ovum surface?

  The acrosome reaction is triggered and enzymes are released
• What happens after one sperm makes it past the ovum's protective barriers?

  • The sperm touches the surface membrane of the secondary oocyte
  • Resulting in the oocyte completing its second meiotic division and forming a haploid nucleus
• Why is it essential that only one sperm touches the oocyte surface membrane?

  Prevents polyspermy
• Why do ion channels in the cell membrane of the ovum open and close?

  Creates a positively charged outside of the cell so that no more sperm can enter
• What happens after the head of the sperm enters the oocyte?

  • The sperm absorbs water and swells
  • Releases chromosomes
• Stage 1 of human fertilisation

  • Sperm can survive 1-2 days in the female reproductive tract
  • As sperm moves through the female reproductive tract, the acrosome matures so that it can release enzymes to penetrate the ovum
• Stage 2 of human fertilisation

  • The ovum released at ovulation has not fully completed meiosis - it is a secondary oocyte with one polar body
  • Ovum surrounded by a protective layer known as the zona pellucida
  • Sperm cluster around ovum - when sperm touches zona pellucida, acrosome reaction is triggered and enzymes are released
• Stage 3 of human fertilisation

  • One sperm eventually makes it past the now-weakened protective barriers of the ovum
  • Sperm touches surface membrane of oocyte - oocyte completes second meiotic division to form a haploid nucleus
  • Vital that no more sperm touch the surface membrane or polyspermy will occur
  • Ion channels in the cell membrane of the ovum open and close - outside of the cell becomes positive so that no more sperm can enter (only a temporary measure until the formation of the fertilisation membrane)
• Stage 4 of human fertilisation

  • Head of sperm enters oocyte
  • Absorbs water and swells
  • Releases chromosomes
  • which fuse with chromosomes of the ovum to form a diploid zygote
• Acrosome


  Region at sperm head containing enzymes
• Zona pellucida


  Jelly-like protective layer around the unfertilised ovum
• Polyspermy


  The fertilisation of an egg by more than one sperm
• Fertilisation membrane

  A tough layer that forms around the fertilised ovum
• Conception


  Fertilisation of the ovum in humans