Sperm

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Basics

Sperm transport

  • Only a very small number of sperm(~50-100) reach the vicinity of the cumulus/oocyte complex
  • Their transport involves several steps:
    1. Vaginal sperm (~250 000 000)
      • The initial ejaculate
    2. Utirine sperm (~100 000)
      • Migration through the cervical mucus seems to occur by the sperm's own innate motility
      • The relatively low viscosity of this mucus at mid-cycle may aid sperm movement at this time
    3. Ampullary sperm (~50)
    4. Ampullary-isthmic delay
      • Upon reaching the isthmus the sperm are apparently "stored" for a period of time (a few hours)
      • This is likely when capacitation occurs


Sperm processes

Freshly ejaculated sperm are incapable of fertilizing ova. Several changes must take place. These fall into three categories:

Capacitation

  • Usually occurs in the female reproductive tract
  • The details are sketchy at best
  • the metabolic rate of sperm increases
  • changes in the protein components of the sperm head and changes in flagellar movement occur
  • These changes prepare the sperm for the recognition and binding to the zona pellucida
  • The change in motility pattern is from progressive forward motility to hyperactivated with a whiplash type of flagellar movement
  • This motility pattern seems to drive the sperm through the cumulus layer and the zona pellucida

Binding to the zona pellucida

  • Because of the specificity, which is achieved by classic ligand-receptor interaction, this process is currently being manipulated in an attempt to develop new contraceptive strategies
  • The binding process may be the trigger for the acrosome reaction

Acrosome reaction

  • occurs at the outer surface of the zona pellucida
  • Involves distinct changes in the head of the sperm such that the enzymes in the acrosome are exposed to the extracellular space and are activated.