Male and female reproductive systems

The female reproductive system consists of two ovaries, two fallopian tubes, the uterus, and the vagina. An ovary normally produces an egg (ovulation) about 11 to 17 days before the woman's next menstrual period, or approximately once a month. The egg is released from the ovary into a fallopian tube and swept by tiny hairlike cells (cilia) and muscle action into the uterus.

See an illustration of the female reproductive system.

The male reproductive system consists of the penis, two testicles, two epididymides, two vas deferentia, two seminal vesicles, and the prostate gland.

Sperm develop in the testicle and finish maturing in the epididymis. When the man comes (ejaculation), the sperm move out of the epididymides through the vas deferens and into the tube (urethra) that runs through the penis. Semen (the thick liquid associated with sperm) is produced in the seminal vesicles and prostate gland and added to the sperm before ejaculation from the penis. Semen protects the sperm from the acid environment in the vagina.

See an illustration of the male reproductive system.

For pregnancy to occur, sperm must travel up the vagina through the uterus and into the fallopian tube to combine with an egg (fertilization) soon after ovulation. The fertilized egg must then implant in the lining of the uterus.

Hormones and reproduction

In both men and women, reproduction begins in the brain. A part of the brain (hypothalamus) produces a substance called gonadotropin-releasing hormone (GnRH). GnRH causes the pituitary gland to release two hormones into the bloodstream: luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

In men, LH causes the release of the male hormone testosterone, while FSH causes the testicles to produce sperm. In women, LH and FSH cause eggs to mature and be released (ovulation). They also cause production of the female hormones estrogen and progesterone.

Many problems with infertility are caused by too little or too much of these hormones, the pattern of hormone levels over time, or problems in the hypothalamus or pituitary gland.