The ovaries are a pair of small reproductive organs located in the pelvis. They have two major jobs: they produce eggs (oocytes) and they make reproductive hormones, especially estrogen and progesterone. Together, these functions connect the ovaries to ovulation, the menstrual cycle, fertility, pregnancy preparation, and many aspects of reproductive development.
Although the ovaries are often described simply as the organs that release eggs, their biology is more complex. An ovary contains a finite population of immature egg cells, supports their development within specialized structures called follicles, responds continuously to signals from the brain and pituitary gland, and changes its hormone production during the menstrual cycle and across the reproductive lifespan.
Where the ovaries are and what they look like
The ovaries normally lie on either side of the uterus within the pelvis. Their position is not completely fixed; the ovaries can shift somewhat within the pelvic cavity as the uterus and surrounding tissues change.
In adults, an ovary is roughly almond-shaped, although its size and appearance vary with age, hormonal state, pregnancy history, and other factors. Each ovary is connected to surrounding structures by ligaments and by a fold of tissue associated with the broad ligament. Blood vessels, lymphatic vessels, and nerves reach the ovary through the suspensory ligament of the ovary.
The ovary has an outer region called the cortex and a more central medulla. The cortex contains ovarian follicles at different stages of development. The medulla contains connective tissue, blood vessels, lymphatic vessels, and nerves.
The surface of the ovary is covered by a thin layer of cells sometimes called the ovarian surface epithelium. Despite the traditional term “germinal epithelium,” these cells do not produce the egg cells.
Ovarian follicles and the development of eggs
The functional unit that supports an immature egg is the ovarian follicle. A follicle consists of an oocyte surrounded by supporting cells that nourish and regulate it.
A person with ovaries is born with a large but finite number of immature oocytes. Most never complete development. Over time, the ovarian reserve—the remaining population of follicles—declines through a combination of follicle development and natural loss.
During each menstrual cycle, a group of follicles begins developing in response to hormonal signals. Usually, one follicle becomes dominant and continues toward ovulation. The developing follicle produces hormones, including estrogen, while the oocyte inside it undergoes important cellular changes.
The term egg is commonly used for the female reproductive cell, but biologically the cell released at ovulation is a secondary oocyte. It completes the final stage of meiosis only if fertilization occurs.
How ovulation works
Ovulation is the release of a secondary oocyte from a mature ovarian follicle. It occurs as part of a coordinated hormonal process involving the hypothalamus, pituitary gland, and ovary.
The hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses. GnRH stimulates the pituitary gland to release two gonadotropins: follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
FSH promotes the growth and activity of ovarian follicles. As a dominant follicle develops, its supporting cells produce increasing amounts of estrogen. When estrogen remains sufficiently high for a sustained period, its feedback relationship with the brain and pituitary changes. Instead of suppressing gonadotropin release, estrogen helps trigger a large LH surge.
The LH surge causes a series of changes in the dominant follicle that culminate in ovulation. The follicle ruptures and releases the secondary oocyte, which is then captured by the nearby end of the fallopian tube.
The ovary does not release an egg directly into the uterus. After ovulation, the oocyte enters the fallopian tube, where fertilization can occur if sperm are present.
What happens to the follicle after ovulation
Ovulation does not mark the end of the follicle’s hormonal role. After releasing the oocyte, the follicle reorganizes into a temporary endocrine structure called the corpus luteum.
The corpus luteum produces substantial amounts of progesterone as well as estrogen. Progesterone changes the lining of the uterus, making it more suitable for implantation and helping maintain the uterine environment during the early part of a potential pregnancy.
If pregnancy does not occur, the corpus luteum eventually loses its function. Progesterone and estrogen levels fall, contributing to the shedding of the uterine lining during menstruation. The ovarian cycle then begins another round of follicular development.
If pregnancy occurs, hormonal signals from the early embryo and developing placenta maintain the corpus luteum for a period of time so that progesterone production continues while the placenta develops its own capacity for hormone production.
The hormones made by the ovaries
The ovaries are endocrine organs as well as reproductive organs. Their hormones act locally within reproductive tissues and throughout the body.
Estrogen
Estrogen is a group of steroid hormones, with estradiol being the predominant form during the reproductive years. Developing ovarian follicles are an important source of estradiol.
Estradiol helps regulate the menstrual cycle and promotes growth and maintenance of the uterine lining. It also contributes to the development and maintenance of reproductive tissues and secondary sex characteristics. Estrogen has effects beyond reproduction, including important roles in bone health and other tissues throughout the body.
Estrogen production is not constant. It rises and falls as follicles develop, ovulation occurs, and the corpus luteum forms and eventually regresses.
Progesterone
Progesterone is produced primarily by the corpus luteum after ovulation during the menstrual cycle. Its major reproductive role is to prepare and maintain the uterine lining in a state that can support implantation.
Progesterone also changes the physical properties of cervical mucus and influences the reproductive tract and breast tissue. Its levels are generally much higher after ovulation than during the earlier part of the cycle.
During pregnancy, progesterone production eventually becomes primarily a function of the placenta rather than the ovary.
Androgens
The ovaries also produce smaller amounts of androgens, a class of hormones that includes testosterone and androstenedione. Ovarian androgens can serve as precursors for estrogen production and contribute to normal reproductive physiology.
Androgens are also produced by the adrenal glands, so circulating androgen levels reflect contributions from more than one organ.
Inhibins and other ovarian hormones
Ovarian follicles produce inhibin, a hormone involved in regulating FSH secretion. Inhibin helps provide feedback to the pituitary as follicles develop.
The ovary also produces other signaling molecules, including anti-Müllerian hormone (AMH), which is produced by certain developing follicles. AMH levels reflect aspects of the population of growing follicles and are used clinically in some assessments of ovarian reserve. However, AMH is not a direct measurement of the number or quality of a person’s remaining eggs, nor does it by itself determine whether someone can become pregnant.
How the ovaries interact with the brain
Ovarian activity is controlled through the hypothalamic-pituitary-ovarian (HPO) axis.
The hypothalamus releases GnRH, which stimulates the pituitary to release FSH and LH. These hormones act on the ovaries, which respond by developing follicles, ovulating, and producing estrogen, progesterone, inhibin, and other hormones. Ovarian hormones then feed information back to the hypothalamus and pituitary.
Most of this feedback is negative: rising ovarian hormones generally reduce further stimulation of the reproductive axis. The important exception occurs before ovulation, when sustained high estrogen levels contribute to positive feedback that produces the LH surge.
This feedback system explains why changes in one part of the reproductive axis can affect the others. Disorders involving the hypothalamus, pituitary, or ovaries can interfere with ovulation or menstrual cycling.
The ovaries and the menstrual cycle
The ovarian cycle and the uterine menstrual cycle are related but not identical.
The follicular phase begins with menstruation and continues until ovulation. During this phase, follicles develop in the ovary and estrogen levels generally rise as the dominant follicle matures.
Ovulation occurs around the middle of the cycle in a typical cycle, but its timing can vary considerably from person to person and from cycle to cycle.
The luteal phase follows ovulation. The corpus luteum produces progesterone and estrogen, which influence the uterus and provide feedback to the brain and pituitary. If pregnancy does not occur, the corpus luteum regresses, hormone levels decline, and menstruation begins.
The length of the follicular phase is generally more variable than the luteal phase. This is one reason the timing of ovulation can differ between cycles.
What happens to the ovaries during menopause
The ovaries change substantially as the ovarian follicle population becomes depleted.
Menopause is defined by the permanent cessation of menstrual periods resulting from loss of ovarian follicular activity. It is a process rather than an abrupt transformation of the ovaries on a single day. During the transition known as perimenopause, ovarian hormone production becomes increasingly variable, menstrual cycles may become irregular, and ovulation becomes less predictable.
After menopause, the ovaries produce much less estrogen and progesterone because functional follicles have become greatly depleted. The ovaries do not become hormonally inactive, however; they continue to produce some steroid hormones, including androgens, and tissues elsewhere in the body can convert some of these hormones into estrogen.
The decline in ovarian estrogen has effects throughout the body. Changes can include menstrual cessation, hot flashes and other vasomotor symptoms, changes in the vaginal and urinary tissues, and increased bone loss.
Ovarian reserve and fertility
Ovarian reserve refers broadly to the remaining population of ovarian follicles capable of contributing to reproductive function. It is different from fertility itself.
A person’s ability to become pregnant depends on multiple factors, including whether ovulation occurs, the condition of the reproductive tract, sperm factors, timing, age-related changes in oocyte quality, and other health and biological factors.
Tests such as AMH levels and an ultrasound measurement of antral follicles can provide information about aspects of ovarian reserve. These measures are useful in particular clinical settings, but they should not be interpreted as a simple “fertility score.” Ovarian reserve tests cannot precisely predict whether an individual will or will not become pregnant naturally.
Age matters because both the number of remaining oocytes and, importantly, the probability of chromosomal abnormalities in oocytes change over time. Declining fertility with age therefore reflects more than a reduction in the number of available follicles.
Common conditions affecting the ovaries
Ovarian disorders range from benign conditions to diseases that require urgent treatment.
Functional ovarian cysts are fluid-filled structures associated with normal follicular development or the corpus luteum. Many resolve without treatment. Some cysts, however, can cause pain, bleeding, or complications such as ovarian torsion.
Polycystic ovary syndrome (PCOS) is a hormonal and metabolic disorder that commonly involves irregular or absent ovulation, increased androgen activity, and characteristic changes in ovarian follicle development. Despite its name, ovarian cysts are not required for the diagnosis.
Endometriosis can involve tissue resembling the uterine lining growing outside the uterus. When it affects the ovary, it can produce an endometrioma, sometimes called a “chocolate cyst” because of its old-blood contents.
Ovarian insufficiency occurs when ovarian function declines before the expected age of natural menopause. It can lead to irregular or absent periods, reduced fertility, and lower estrogen levels.
Ovarian cancer is a group of cancers arising from different cell types in or associated with the ovary. The term encompasses several biologically distinct diseases, and their symptoms, behavior, and treatment can differ substantially.
When ovarian symptoms deserve medical attention
Pelvic or abdominal pain does not necessarily mean there is a problem with the ovaries, but certain symptoms warrant prompt evaluation. Severe or sudden pelvic pain, particularly when accompanied by nausea or vomiting, can occur with conditions such as ovarian torsion or a ruptured ovarian cyst and should be assessed urgently.
Persistent pelvic or abdominal symptoms, unexplained changes in menstrual bleeding, a new pelvic mass or swelling, or symptoms associated with possible hormonal dysfunction also merit discussion with a healthcare professional.
The ovaries normally undergo significant hormonal changes throughout life, so an irregular period or pelvic symptom cannot be interpreted accurately from the symptom alone. Diagnosis may involve a medical history, physical examination, pregnancy testing when appropriate, hormone testing, and pelvic imaging depending on the situation.
The ovaries are therefore both reproductive and endocrine organs: they support the development and release of oocytes while coordinating a changing pattern of hormone production. Their activity is governed by a tightly regulated conversation among the hypothalamus, pituitary gland, and ovaries, and that system changes naturally from puberty through the reproductive years and into menopause.
