AP BIOLOGY

Detailed explanation-1: -A blastocyst is a ball of cells that forms early in a pregnancy, about five to six days after a sperm fertilizes an egg. It implants in your uterine wall, eventually becoming the embryo and then the fetus.

Detailed explanation-2: -During fertilization, the sperm and egg unite in one of the fallopian tubes to form a zygote. Then the zygote travels down the fallopian tube, where it becomes a morula. Once it reaches the uterus, the morula becomes a blastocyst. The blastocyst then burrows into the uterine lining-a process called implantation.

Detailed explanation-3: -Implantation. Once the embryo reaches the blastocyst stage, approximately five to six days after fertilization, it hatches out of its zona pellucida and begins the process of implantation in the uterus.

Detailed explanation-4: -During apposition process, the blastocyst differentiates into an inner cell mass (embryo) and trophectoderm (placenta). Stromal cells surrounding the implanting blastocyst differentiate into a specialized cell type called decidual cells, via a process known as decidualization (Ramathal et al., 2010).

Detailed explanation-5: -A blastocyst successfully implants in the uterus when, as the ZP exits the fallopian tube, the blastocyst leaves the ZP and binds to the endometrium. The endometrium is one of the few uterine surfaces to which a blastocyst cannot always implant.