PROF. P. MOTTA / S. NOTTOLA / G. FAMILIARI / UNIVERSITY"LA SAPIENZA" / ROME / SCIENCE PHOTO LIBRARY PROF. P. MOTTA / S. NOTTOLA / G. FAMILIARI / UNIVERSITY"LA SAPIENZA" / ROME / SCIENCE PHOTO LIBRARY
False-colour scanning electron micrograph of a human egg from an in vitro fertilisation program. Part of the external layer of follicular cells (yellow and violet), called the corona radiata, was removed. This reveals the zona pellucida (red at top centre), a thin but resistant glycoprotein layer which entirely surrounds the egg. Zona pellucida and corona radiata provide nutrients and protection to the ovum and represent a barrier for the spermatozoa. The penetration of the corona radiata and zona pellucida occurs thanks to enzymes released by the spermatozoa. Magnification: x1570 at 6x7cm size.
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