Understanding the Function of Ovaries

The ovaries are a key part of the normal development and reproductive function of women.

Anatomy

Ovaries are a pair of glands (approximately the size and shape of an almond) in the female reproductive system where eggs are stored and estrogen is manufactured. They are held in place by several ligaments on either side of the uterus. 

Eggs are transported from the ovaries to the uterus via the fallopian tubes. Surrounding the entrance to the fallopian tubes are tiny fimbriae, or fingerlike projections, which guide the egg into the tube each month.

The Ovaries Through Your Lifespan

You are born with all of the eggs you’ll ever need, around 1 million in each of the ovaries. By puberty, when you’ll most likely receive your first period, the number of eggs in each ovary is around 200,000–400,000. During the childbearing years, approximately 300–500 eggs will develop and be released during ovulation.

After menopause, the ovaries will stop producing eggs and atrophy (shrink). Due to a loss of ovarian functioning and loss of estrogen production, postmenopausal people commonly experience symptoms like hot flashes and vaginal dryness. Estrogen deficiency also increases your risk of developing osteoporosis, which increases your risk of bone fracture.

The Ovaries' Role in the Menstrual Cycle

While cycles may be irregular in the beginning, they will eventually become more regular, with the start of one period being about 28 days from the start of the next. Each month, approximately 10–12 egg follicles will begin to develop. One will continue to produce a mature egg. The rest will be reabsorbed into the ovarian tissue.

About 14 days into the menstrual cycle, that mature egg will be released in a process called ovulation. After ovulation occurs, the empty follicle is known as a corpus luteum. It will produce progesterone and other hormones crucial for pregnancy for about 14 days.

Progesterone helps prepare and thicken the lining of the uterus for implantation if fertilization of the egg with sperm occurs. Also, if fertilization does occur, this hormonal support will continue throughout pregnancy to prevent other eggs from maturing. If fertilization does not occur, progesterone levels will decline, the corpus luteum will degenerate, and menstruation will begin.

Hormonal Role of the Ovaries

The ovaries are sensitive to the effects and changes of the endocrine, or hormonal, system. They respond to and produce their own hormones as needed by the body. In fact, the second major role of the ovary is to secrete the sex hormones—estrogen, progesterone, and very small amounts of androgens, which cause the typical female sex characteristics to develop and be maintained.

The ovaries are also a significant source of testosterone for women, especially after menopause.

In addition, the ovaries also respond to FSH and LH which are produced by a small gland in the brain called the pituitary gland. FSH (follicle-stimulating hormone) causes the estrogen level to rise and a group of egg follicles to grow each month. As one follicle becomes dominant and reaches maturity, the higher estrogen level will cause the LH (luteinizing hormone) to surge, triggering ovulation.

Bottom Line

The ovaries and the hormones they produce (notably estrogen and progesterone) play a crucial function in reproductive aging.