Female Role
Conception occurs when a man's sperm fertilizes a woman's egg. Preparations for pregnancy actually begin in a woman's body about two weeks before conception occurs. After a woman's menstrual period ends, levels of the female hormone estrogen begin to rise, according to the National Women's Health Information Center. The increase in estrogen causes a layer of blood and tissue to build up on the uterine walls in preparation to support a newly fertilized egg.
While the lining grows thicker, an egg is maturing in a woman's ovary. Women have two ovaries, one of either side of the uterus, the organ that holds a developing baby. Near the middle of a woman's menstrual cycle, the egg is released and travels from the ovary to the fallopian tube. A fallopian tube connects each ovary to the uterus. Hair-like projections in the fallopian tube push the egg to the mid-point of the tube, where it waits to be fertilized, according to the Dr. Spock website. Mucus produced by the cervix thins as ovulation approaches, allowing sperm to easily swim from the vagina to the uterus.
Male Role
Sperm is produced by the testicles, two sacs located beneath the penis. The testicles make millions of sperm cells that reach the penis by traveling through the epididymis, a set of coiled tubes used to transport semen, according to Kids Health. Semen is a white fluid produced by the prostate gland and the seminal vesicles. Semen is used to nourish the sperm and make it easier for them to propel themselves through a woman's reproductive tract. When a man ejaculates, sperm mix with the semen before exiting the body.
Conception
Sperm are ejaculated from the testicles and travel through the penis and into the woman's vagina when a man has an orgasm, or sexual climax. Sperm swim through the vagina, cervix and uterus before reaching the fallopian tube. Every time a man ejaculates, up to 500 million sperm may be expelled from his body, according to Kids Health. A large number of sperm are needed because many of them die on the journey to the fallopian tube.
A single sperm penetrates the egg and prevents other sperm from entering. Cells inside the fertilized egg begin to multiply, forming a ball of cells called a blastocyst. The blastocyst travels through the fallopian tube, finally reaching the uterus three or four days after ovulation. The blastocyst attaches to the uterine wall five to eight days after fertilization and completely attaches to the uterine lining by the ninth or tenth day, according to the Merck Manuals Online Medical Library. Cells in the interior of the blastocyst thicken and become the embryo, while the outer cells become the placenta. The placenta forms a connection between the baby and the uterus and allows nutrients and oxygen to pass from the mother to the baby.
