Sperm

From IKE

Contents 1 Basics 2 Sperm transport 3 Sperm processes 3.1 Capacitation 3.2 Binding to the zona pellucida 3.3 Acrosome reaction

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.