Reproduction

Human reproduction is when an egg cell from a woman and a sperm cell from a man unite and develop in the womb to form a baby. A number of organs and structures in both the woman and the man are needed in order for this process to occur. These are called the reproductive organs and genitals.

The male reproductive system

In males, the reproductive organs and genitals include:

• testes, also called testicles: a pair of oval-shaped glands that produce sperm
• scrotum: the pouch of skin that contains the testes
• penis: the male reproductive organ, through which urine and semen pass
• prostate gland: a gland that produces some of the fluid part of semen
• seminal vesicles: a pair of glands that also produce some of the fluid part of semen
• vas deferens: a pair of ducts leading from the testes to the seminal vesicle, through which the sperm travel

Male Reproductive System

The female reproductive system

In females, the reproductive organs and genitals include:

• ovaries: two organs on either side of the lower abdomen that release an egg cell on a monthly basis
• vagina: a muscular tube that receives the penis during sex, through which sperm travel on their way to fertilize the egg, and through which a baby passes during childbirth
• fallopian tubes: a pair of tubes running from the ovary to the uterus, through which an egg cell travels, and where fertilization with sperm usually occurs
• uterus: an organ, also called the womb, where the fertilized egg cell implants and grows into the unborn baby during pregnancy
• vulva: the outer folds that surround the openings of the vagina and the opening from the bladder called the urethra

Female Reproductive System

Ovulation and fertilization

Fertilization

Once every month or so, a woman’s ovary releases an egg cell. This process, known as ovulation, usually occurs about 14 days after the start of the woman’s last menstrual period, if she has a normal 28-day menstrual cycle. The egg cell is swept through the fallopian tube, which runs from the ovary to the uterus. The egg cell slows in the longest and widest part of the fallopian tube. This is where the egg cell is fertilized by a man’s sperm cell. During sex, the penis releases a thick, whitish fluid called semen into the woman’s vagina. Semen contains millions of sperm cells that deposit in and around the vagina. Several hundred of these sperm cells pass through the vagina into the uterus. From there, the sperm cells enter the fallopian tubes. The sperm cells surround the egg cell if it is present. When a sperm enters an egg cell, they unite and their chromosomes mingle together. This is called conception or fertilization.
If the egg is fertilized by the sperm cell, the fertilized egg cell begins to divide into two cells, then four, then eight, and so on, while it travels the rest of the way through the fallopian tube to the uterus. There it implants and grows into the unborn baby. If the egg is not fertilized by the sperm, it will eventually be expelled, along with the lining of the uterus, during the woman’s next menstrual period.