How the Reproductive System Works

How the Male Reproductive System Works

The main function of the male reproductive system is to produce sperm. Sperm are produced in the testes once puberty is stimulated by the increased production of testosterone, a sex hormone. Testosterone causes the development of secondary male sex characteristics like the growth of facial and pubic hair and the growth of skeletal muscles.

Sperm from the testes are initially immature and cannot fertilize an egg. After the sperm leave the testes, they mature by combining with molecules and enzymes contained in the seminal fluid. Males continue to produce sperm for the rest of their lives. A healthy male produces about 300,000,000 immature sperm each day.

How the Female Reproductive System Works

The main function of the female reproductive system is to produce eggs, also called ova (plural for ovum), which are the female sex cells. This process begins before birth. Immature female sex cells, or oocytes, begin to develop in the female fetus, but they are held in a semi-developed state of suspended animation in the ovaries.

The ovaries produce two hormones, estrogen and progesterone. Puberty begins with increased hormone production, stimulating secondary female characteristics such as the development of breasts, the growth of underarm and pubic hair, and the widening of the pelvic cavity in preparation for pregnancy.

Starting at puberty, one oocyte a month will mature into an ovum. In a process called ovulation, this single ovum is released from the ovary and travels towards the uterus in a fallopian tube. What happens next depends on whether or not the ovum is fertilized when it combines with a sperm. If the ovum is fertilized by a sperm, pregnancy follows. If an ovum is not fertilized, a set of processes known as the menstrual cycle occurs.

The Menstrual Cycle

The menstrual cycle begins when the ovum released from the ovaries is not fertilized. There is a period of about 2 weeks prior to ovulation during which the lining of the uterus builds up tissue and blood in preparation for a fertilized egg. When no fertilized egg arrives, the uterine lining is released from the body through the vagina during menstruation. After menstruation, which usually lasts for 4 or 5 days, there is a period of about a week before another ovum develops and is released.


Pregnancy occurs when a fertilized egg implants in the uterus. The fertilized egg develops into an embryo, called a fetus in later stages of development into a newborn baby at birth. Pregnancy typically lasts for about 9 months, or 40 weeks.


Females do not continue to produce ova for all of their lives. Ovulation will occur once a month for about 30 to 40 years, after which time ovulation and menstruation cease and the female will no longer be able to reproduce. This is called menopause.

How the Male and Female’s Reproductive Systems Work Together


The union of a sperm and an egg is called conception. These two reproductive cells combine after sexual intercourse when a man releases millions of sperm into a woman’s vagina. However, only about 1,000 of these sperm travel all the way up a woman’s fallopian tube to reach the egg. Many hundreds of sperm surround the egg, but only one sperm fertilizes the egg by penetrating its outer layer and entering its core. Once a sperm penetrates this outer layer of the egg, the layer changes to prevent additional sperm from entering. 

The genetic material of the sperm and egg combine to form a single cell, called a zygote. The zygote floats down the length of the fallopian tube until it reaches the uterus, or womb, implants, and may grow into a fetus.