1 / 54

Fertilization a process at the beginning of ourselves

Fertilization a process at the beginning of ourselves. Structure of Sperm and Egg. Sperm A human sperm. Egg Overview The zona pellucida. Scanning electron micrograph of a human sperm contacting a hamster egg. For detail.

meda
Télécharger la présentation

Fertilization a process at the beginning of ourselves

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Fertilizationa process at the beginning of ourselves

  2. Structure of Sperm and Egg • Sperm A human sperm. • Egg Overview The zona pellucida.

  3. Scanning electron micrograph of a human sperm contacting a hamster egg. For detail

  4. Scanning electron micrograph of a clam egg with sperm bound to its surface. For detail

  5. Block to polyspermy • A depolarization of the egg plasma membrane a rapid, primary block to polyspermy • Egg cortical reaction a slow, secondary block to polyspermy

  6. primary block to polyspermy • Na+ influx triggered by fusing with sperm make the membrane potential of egg shift from –60mV to +20mV within a few second. • Low concentration of Na+ raise the incidence of polyspermy. Artificially depolarized an unfertilized egg prevent sperm from fusing with egg.

  7. primary block to polyspermy • It seems likely that the depolarization alter the conformation of a crucial protein in the egg plasma menbrane so that the sperm membrane can not fuse with the egg membrane. • The egg membrane potencial returns to normal within a few minutes after fertilization.

  8. Therefore • a second mechanism must provide a long-term barrier to polyspermy. • In most egg, including those of mammals, this barrier is provided by Cortical Reaction.Back

  9. Second block to polyspermy • When the sperm fuses with the egg plasma membrane, it activates the inositol phospholipid cell-signaling pathway in the egg. This, in turn, causes a local increase in cytosolic Ca2+, which spreads through the cell in a wave. The rise in Ca2+ activate the egg and initiate the cortical reaction.

  10. Second block to polyspermy • cortical granules located just under the plasma membrane of the egg release their contents by exocytosis. A,B • The enzymes released by the cortical reaction change the structure of the zona pellucida, which becomes hardened so that sperm no longer bind to it, thereby providing a slow, secondary block to polyspermy. End

  11. A mature Xenopus egg, ready for fertilization.For detail

  12. The zona pellucida The zona pellucida. For detail

  13. A human sperm. It is shown in longitudinal section

  14. Drawing of the midpiece of a mammalian sperm

  15. Depolarization&Cortical reactionare the mechanics ofBlock to Polyspermycontinue

  16. AcrosomeReaction • Sperm penetrate the zona pellucida by acrosome reaction. • Process of acrosome reaction. Back

  17. Process of Fertilization • Acrosome reaction • Deplarization • Cortical Reaction • 2nd oocyte complete Meiosis Ⅱ • Pronucleus • Replication of DNA in pronucleus • First Mitosis

More Related