October 22, 2010

Birds and Bees Part IV

When I look into your big brown eyes
It’s so very plain to see
That it’s time you learn about the facts of life
Starting from A to Z (Herb Newman)

Only a few hundred of the millions of sperm deposited actually reach the egg. The sperm like hounds to the hunt are thought to be guided to the egg by her alluring secretions acting like homing beacons. Upon finally reaching the egg by those that could follow directions, the sperm (still as yet a team effort) become hyper-activated, beating their tails in frenzy (like a Golden Retriever with a new toy). This passion provides the mechanical energy necessary for sperm to disperse the cumulous oophorus and bind to the zona pellucida. At this time a chemical is released by the attached sperm in a bombarding-like process called the acrosome reaction. Acrosomal enzymes like barbarians at the gate barrage the zona pellucida by making small holes like individual battering rams so that one victorious sperm of the hundreds lucky enough to be there out of the millions who tried can now triumphantly swim through and reach the egg surface. Once the egg recognizes that her defensive wall has been breached, she transforms her zona into an impenetrable barrier preventing additional sperm from entering and is thereby left alone to dance with the now only one intrepid intruder.

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Joseph A. Hill, III, M.D.

Joseph A. Hill, III, M.D. Board-Certified in Reproductive Endocrinology and Infertility