While many of us tuck into our chocolate eggs today, there are simultaneously tens of thousands of women ovulating across the world. Human eggs are, unlike their male counterparts, rather large cells. Produced by fluid-filled sacs on the side of the ovary, they emerge surrounded by a jelly-like substance containing nutritive cells. So-called follicle cells (coloured pink in this electron micrograph) send out long projections that penetrate through the tough outer coating (the zona pellucida) into the egg itself (here coloured yellow) to nourish it through to maturity. As the egg progresses along the Fallopian tube after ovulation, the cloud of nutritive cells gradually falls away. The human egg can be magnified up to 500,000 times using a scanning electron microscope. In real life, it is roughly the size of a full stop.
Written by Brona McVittie
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences (the new name for the MRC Clinical Sciences Centre) the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.