FERTILIZATION

Fertilization is the union of the male gamete (the sperm) and the female

gamete(the oocyte). Fertilization usually occurs in the ampulla of the fallopian tube

At the fertilization the nucleus of the sperm and the nucleus of the ovum unite to form diploid zygote.

Mitotic cell division occurs after fertilization as the zigot passes down the uterine tube. The zygote divides into 2 cells – 4 – 8 – 16 and so on. The zygotes divides repeatedly to form a round mass 16 cells called a morula, usually on the 3^rd day at approximately the time it enters the uterus. The morula cells continue to multiply as it floats free in the uterine cavity for another 3 – 4 days.

Fertilization and Nidation

After the murola enters the uterine cavity, a fluid-filled cavity appears in the murola, which now becomes known as the blastocyst. Around the outside of the blastocyst there is a single layer of cells known as the trophoblast. The remaining cells are clumped together at 1 end forming the inner cell mass.

The trophoblast will form the placenta and chorion. The inner cell mass will become the embryo, the amnion and the yolk sac membrane. The trophoblast cells secrete enzymes that allow the blastocyst to become embendded in the endometrium. Nidation is normally complete by the 11^th day after ovulation.