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The zonal reaction

Very high power TEM of a stage 1a embryo in vitro showing the zonal reaction, 72 hours post-insemination (original magnification x65,450). Secretory products of two cortical granules in the subzonal space (SS) are interacting with the zona pellucida (Z). The released contents of the cortical granules have decondensed but retained their shape (arrowhead). The cortical granule material appears to be diffusing into the zona pellucida which may be the morphological feature of the zonal reaction. A microvillus with intact cortical granules and microvilli (Mv) are evident in the subzonal space at the embyro surface.

Cy = cytoplasm

From: Sathananthan and Trounson, 1982. Reproduced with permission of the publisher, John Wiley & Sons.

Keywords: cortical granule(s), cytoplasm, microvilli, stage 1a embryo, subzonal space, zonal reaction

Source: The Virtual Human Embryo.