The ovaries belong to two body systems: the reproductive system and the endocrine system. This dual membership makes them unusual. Most organs serve one system, but the ovaries pull double duty, producing eggs for reproduction while also releasing hormones that influence tissues throughout the body.
The Reproductive System Role
In the reproductive system, the ovaries are the primary organs. Their core job is producing and releasing eggs (also called ova) that can be fertilized to create a pregnancy. Each ovary contains a reserve of immature eggs stored inside tiny fluid-filled sacs called follicles. At birth, the ovaries hold roughly 1 to 2 million of these primordial follicles. By puberty, that number drops to about 400,000 to 500,000, and by menopause only around 1,000 remain.
Starting at puberty, one egg typically matures and is released each menstrual cycle in a process called ovulation. The egg travels from the ovary into the fallopian tube, where it can meet sperm. If it isn’t fertilized, it breaks down, and the uterine lining sheds during a menstrual period. This cycle repeats roughly every 28 days, though normal cycles range from 21 to 35 days.
The ovaries sit in the pelvis, one on each side of the uterus. They’re small, roughly the size and shape of an almond, and are held in place by ligaments that connect them to the uterus and pelvic wall.
The Endocrine System Role
The endocrine system is the body’s hormone network. It includes glands like the thyroid, adrenal glands, pancreas, and the ovaries. As endocrine glands, the ovaries produce two major hormones: estrogen and progesterone. These aren’t just reproductive hormones. They affect bone density, cardiovascular health, mood, skin, and fat distribution.
Estrogen drives many of the changes that begin at puberty: breast development, the widening of hips, fat distribution around the hips and thighs, and maturation of the uterus and vagina. It also plays a protective role in bone health and heart function throughout the reproductive years.
Progesterone works in tandem with estrogen to regulate the menstrual cycle. After ovulation, progesterone levels rise sharply, thickening the uterine lining to prepare for a potential pregnancy. If no pregnancy occurs, progesterone drops, triggering the lining to shed. During the second half of the cycle (the luteal phase), progesterone levels are roughly 130 times higher than they are during the first half.
How the Brain Controls the Ovaries
The ovaries don’t operate independently. They’re regulated by a communication loop between the brain and the ovaries, often called the hypothalamic-pituitary-ovarian axis. Here’s how it works: a region at the base of the brain (the hypothalamus) releases a signaling hormone in pulses. This tells the pituitary gland, a pea-sized gland just below it, to release two hormones called FSH and LH into the bloodstream.
FSH stimulates follicles in the ovary to grow and produce estrogen. As estrogen rises, it signals back to the brain, which adjusts how much FSH and LH it releases. Near the middle of the cycle, a sharp surge of LH triggers ovulation, releasing the mature egg. After ovulation, the empty follicle transforms into a temporary structure that pumps out progesterone. This feedback loop keeps the entire system in balance. When it breaks down, menstrual irregularities and fertility problems can follow.
What Happens When Ovarian Function Is Disrupted
Because the ovaries sit at the intersection of two systems, problems with ovarian function can ripple outward in both reproductive and metabolic ways. The most common example is polycystic ovary syndrome (PCOS), which affects hormonal signaling and leads to higher than normal levels of androgens (sometimes called “male hormones,” though all women produce them in small amounts).
PCOS is diagnosed when a person has at least two of the following: signs of excess androgens (such as acne, excess facial or body hair, or thinning hair on the scalp), irregular or absent periods, or polycystic-appearing ovaries on an ultrasound. Despite the name, ovarian cysts aren’t actually required for diagnosis. PCOS is more than a reproductive issue. The World Health Organization classifies it as a chronic metabolic condition that persists beyond the reproductive years. People with PCOS face increased risks of type 2 diabetes, high blood pressure, high cholesterol, cardiovascular disease, and endometrial cancer. It can also significantly affect mental health, contributing to anxiety, depression, and disordered eating.
Another condition, primary ovarian insufficiency (sometimes called premature ovarian failure), occurs when the ovaries stop functioning normally before age 40. Because the ovaries are a major source of estrogen, losing that function early affects far more than fertility. It can accelerate bone loss, raise cardiovascular risk, and cause symptoms like hot flashes and vaginal dryness that are typically associated with menopause.
Why the Dual Role Matters
Understanding that the ovaries serve two systems helps explain why ovarian health affects so much more than periods and pregnancy. When hormone production declines during menopause, for instance, the effects show up across the body: bone density decreases, cholesterol profiles shift, and the risk of heart disease rises. These aren’t reproductive consequences. They’re endocrine consequences, stemming from the loss of hormones the ovaries had been steadily producing for decades.
It also explains why treatments that suppress ovarian function, such as certain cancer therapies or surgical removal of the ovaries, require careful consideration of hormonal replacement. Removing the ovaries doesn’t just end fertility. It removes a major endocrine gland, and the body feels that absence in systems that have nothing to do with reproduction.