How the Female Reproductive System Works

The female reproductive system is pretty amazing and allows a woman to do some really important things:

1. Produce eggs (ova)
2. Engage in sexual intercourse
3. Protect and nourish a fertilized egg until it’s fully developed
4. Give birth

When we think about reproduction, many of us picture male gonads, like testicles. But did you know that females also have gonads? For women, the gonads are the ovaries, which produce the eggs.

When a baby girl is born, her ovaries already contain hundreds of thousands of tiny, inactive eggs. These eggs stay dormant until she hits puberty. Once puberty begins, the pituitary gland in her brain starts releasing hormones that kick the ovaries into gear, stimulating the production of female sex hormones like estrogen. This is what helps a girl grow into a sexually mature woman.

Toward the end of puberty, girls begin to experience a monthly cycle called the menstrual cycle. About once a month, during a phase known as ovulation, an ovary releases a tiny egg that travels into one of the fallopian tubes.

If that egg doesn’t get fertilized by sperm, it leaves the body about two weeks later during menstruation. This involves some blood and tissue from the inner lining of the uterus, which forms the menstrual flow—a process that usually lasts between 3 to 5 days.

If a female and male have sex a few days after ovulation, there’s a chance fertilization can happen. When the male ejaculates, a small amount of semen containing millions of sperm is deposited into the vagina. Those sperm “swim” up through the cervix and uterus to meet the egg in the fallopian tube. It only takes one sperm to fertilize the egg!

About 5 to 6 days after fertilization, the tiny fertilized egg, called a zygote, transforms into a multicelled blastocyst. This blastocyst, comparable in size to a pinhead, is a hollow ball of cells that then burrows into the lining of the uterus, known as the endometrium. Estrogen helps make the endometrium rich and thick with blood, while another hormone, progesterone, supports this lining so that the blastocyst can attach and gather nutrients. This is the start of a process called implantation.

Once implantation occurs, the next stage of development kicks in! The inner cells form a shape known as the embryonic disk, which will eventually become a baby. The outer cells develop into membranes around the baby. These cells multiply rapidly and move into new positions, forming the embryo.

After about 8 weeks, the embryo is about the size of a raspberry, and most of its essential parts like the brain, heart, and skin are already formed.

During the fetal stage, which lasts from 9 weeks after fertilization until birth, development is ongoing. The fetus floats in a protective fluid inside the amniotic sac and gets oxygen and nutrients from the mother’s blood through the placenta. The placenta is a special structure that attaches to the inner lining of the uterus, ensuring that the developing fetus has everything it needs to grow.