- Zona pellucida
- The strong membrane that forms around an ovum as it develops in the ovary. The membrane remains in place during the egg’s travels through the fallopian tube. To fertilize the egg, a sperm must penetrate the thinning zona pellucida. If fertilization takes place, the membrane disappears to permit implantation in the uterus.
* * *zona pel·lu·ci·da -pə-'lü-sə-də n the transparent more or less elastic noncellular glycoprotein outer layer or envelope of a mammalian ovum often traversed by numerous radiating striae
* * *the thick membrane that develops around the mammalian oocyte within the ovarian follicle. It is penetrated by at least one spermatozoon at fertilization and persists around the blastocyst until it reaches the uterus. See ovum.
* * *1. pellucid zone: a thick, transparent, noncellular layer or envelope of uniform thickness surrounding an oocyte; called also oolemma. Under the light microscope it appears as a radially striated layer; under the electron microscope this can be seen to be microvillous, so that it is called the z. radiata, z. striata, or striated membrane. 2. area pellucida.
Medical dictionary. 2011.