The gonads form a part of the endocrine system and are the primary reproductive organs of both sexes. Ovaries are the female gonads. Testes are the male gonads. They are generally considered mixed glands in both sexes because they manufacture both cells and hormones. The hormones and cells they produce are vital to reproduction.

The endocrine system consists of the gonads, the pancreas, the thyroid glands, the pituitary gland and hypothalamus, the pineal gland, and the adrenal gland. The glands of the endocrine system are responsible for producing the hormones that help regulate all of the body's processes. The gonads are responsible for manufacturing reproductive hormones such as testosterone, progesterone, and estrogen in both sexes.

The gonads are essential reproductive organs because they produce gametes, or reproductive cells. Sperm are the male gamete, produced by the male gonads, the testes. Ovum, or eggs, are the female gamete, produced by the female gonads or ovaries. Fertilization occurs when the male and female gametes, or reproductive cells, meet and merge. This process is known as conception, and is generally followed by the development of a fetus and then the birth of an infant.

In the female, the ovaries are the gonads. The ovaries usually produce the female reproductive hormones progesterone and estrogen. They also produce the female egg, which is essential to reproduction. The ovaries regulate ovulation, which controls the release of the egg for fertilization. In the female, the ovaries are responsible for controlling fertility and reproductive cycles.

Female reproductive hormones also typically affect the development of female sexual characteristics and other sex organs, such as the breasts. They can regulate the activity of the uterus, including menstruation. They are also responsible for controlling sexual feelings and desire. The hormone progesterone may aid in pregnancy by preparing the uterus for conception and preventing miscarriage of the embryo.

In the male, the testes are the gonads. The testes produce sperm as well as the male reproductive hormone, testosterone. In the male, testosterone generally affects the development of secondary and other reproductive organs. Testosterone is responsible for male sexual characteristics, such as body hair and a deeper voice. Testosterone may also help control male sexual feelings and desire.