Ovaries
Fertilization begins with a female's ovaries. The ovaries are two round balls located on both sides of the uterus. The ovaries are responsible for storing the many eggs that, if given a chance to be fertilized, can transform into a fetus. Starting with a female's first period, the ovaries start releasing matured eggs through the fallopian tubes into the uterus. This process is called ovulation. If the egg is not fertilized, it will be removed from the uterus through menstruation.
Sperm
The female egg requires a male counterpart known as sperm. Sperm are produced in two male glands called testicles, which are housed in a sack known as the scrotum. When a man reaches puberty, these glands begin producing sperm. The sperm are released through a series of ducts that allow the sperm to be combined with other fluids from the prostate and seminal vesicles to produce seminal fluid or "semen," which can then exit the penis during ejaculation. Once a man becomes sexually excited, the corpora cavernosa of the penis fills with blood, making it hard and rigid. This allows the penis to enter the female and project the sperm into the female reproductive tract.
Fertilization
Once the sperm enters the female reproductive tract, they slowly make their way from the cervix, through the uterus and into the fallopian tubes. If a mature egg is present in the fallopian tube, and even one sperm has made it through the acidity of the vagina and the mucus of the cervix, it can fertilize the egg. Fertilization occurs when the sperm is able to open a way through the shell of the egg to reach its center. The genetic material of the egg then combines with the genetic material of the sperm to form an embryo.
