The body's largest cell is the egg, a woman born, both sides of the ovary has stored millions of undeveloped follicles, to adulthood after the remaining more than 100 thousand. But about 400 or so in life can really mature, released by the ovary, play the role of creating life. And the rest will be degraded. During each menstrual cycle, two ovaries alternate with ovulation (possibly from one ovary), and the ovaries can develop with multiple follicles at the same time, but usually only one egg matures.
       Each mature follicle contains an egg cell surrounded by follicular fluid and follicular wall. The process of follicular development and endocrine function, mainly estrogen secretion during the menstrual cycle, the middle time, when follicular maturation, follicular secretion of estrogen peak in vivo estrogen stimulate the pituitary gland to release a large number of luteinizing hormone (LH hormone), mature ovarian follicle wall to rupture, follicular fluid outflow after oocyte discharge this is a mature egg. A few minutes after the egg discharge, then through the fallopian tube umbrella "pick" and into the fallopian tube of the ampulla. Here the liquid flow rate is slow, there are abundant adrenergic nerve fibers, including the role of the ability to retain eggs, waiting for the sperm to come, there is the possibility of pregnancy. Therefore, fallopian tube patency is one of the keys to meet and combine eggs and sperm.
       Sperm is discharged from male urethra, there are hundreds of millions of ejaculation, through the vagina, cervix, uterus to reach the fallopian tube, and finally only a few sperm to reach the fallopian tube of the ampulla. The rest is excreted by the vagina or swallowed by the white cells in the uterus and disappeared into the abdominal cavity. Usually sperm in 1-3 days with the ability to fertilize.
       Egg survival time only 24 to 36 hours. Simple calculation, may before ovulation in 3 days or 2 days after ovulation. This time the couple have conceived.
       Human mature sperm and egg cells each contains 23 pairs of human cells containing half of the chromosomes of the 23 chromosomes, each with half the necessary DNA. The sperm into the egg, the bigger nucleus to similar and egg nuclei, sperm nuclei (male pronucleus) and egg nuclei (female pronucleus) at the same time close to the egg cell central, and merging into a nucleus, the chromosome is mixed together, then the egg is called a fertilized egg. Once the eggs and sperm chromosomes together, the fertilized egg will according to the instructions of DNA chromosome began development, fertilization occurs a few hours later, the first division (cleavage), initially split into two cells, two cells split into 4 cells, 4 cells and then split into 8. So continue to split. Each cell copies a full set of DNA when it splits.