Describe the events associated with fertilization and early development

Question

What will be an ideal response?

Answer 1

Sperm deposited in vagina travel through cervical canal, uterus, and to upper third of oviduct. Female reproductive tract aids in sperm migration via contractions of myometrium and upward contractions of oviduct smooth muscle. After ovulation the ova is picked up by the oviduct through the actions of fimbriae, the finger-like projections at the distal end of the oviduct. Once inside, the ovum is moved along via the actions of cilia that line the oviduct. Fertilization occurs when the sperm reaches the ovum and fuses with plasma membrane of ovum. This triggers chemical change in the ovum's surrounding membrane that makes outer layer impermeable to entry of any more sperm. The head of the fused sperm is gradually pulled into the ovum's cytoplasm, and within an hour sperm and egg nuclei fuse. Fertilized ovum is now called a zygote.
The blastocyst implants in the endometrial lining by means of enzymes released by trophoblast cells. These enzymes digest endometrial tissue, carving a hole in endometrium for implantation of blastocyst. The endometrial tissue is modified at the implantation site and is known as the decidua. The placenta is formed when projections of fetal chorionic tissue forms placental villi, which protrude into a pool of maternal blood. The chorionic tissue erodes decidual capillary walls and maternal blood leaks out and fills the cavities. Fetal capillaries then extend into the placental villi where it can now exchange materials with maternal blood.