The covering over the embryo is called zona pellucida. It’s main function is to protect the embryo and maintain its integrity as it travels through the oviduct into the uterine cavity . Once it reaches the cavity blastocysts must get out of the ZP ( hatching )so that the trophectoderm cells can interact with the Endometrial cells and implantation can occur . Zona hardening occurs after fertilisation and this is a physiological phenomenon to… Read More