The female reproductive system is composed of two ovaries to produce ova, or eggs. There are two tubes called oviducts that are connected to the uterus or womb. The oviduct is where the egg waits to be fertilized by a sperm cell in a sexually active female. The uterus supports the growth and development of the embryo and later on, the fetus. The vagina is the birth canal through which the baby is born. There are hormones called estrogen and progesterone which maintain the menstrual cycle and a pregnancy if one arises. Males have two testes, which are the essential male organs that produce both sperm and testosterone, the male hormone. Sperm cells are male gametes that join with an egg to produce an offspring. There are two vas deferens or sperm ducts that connect the testes to the urethra, a tube that runs through the penis and is the way for the sperm to leave the body, via ejaculation. There is a liquid called semen that blends with the sperm, and is produced by seminal vesicles, prostate gland and cowper's glands. This liquid aids the sperm's journey to the egg by providing a medium for sperm to swim in. During sexual intercourse, the penis deposits sperm in the female vagina. If an egg cell is present in the oviduct and a sperm cell swims up to the cervix, the uterus and to an oviduct with a waiting egg cell and joins with it, fertilization occurs. These systems become active after puberty.