The female gonads, known as the ovaries, are important reproductive organs. They serve two primary roles: producing ova (egg cells) for reproduction, and functioning as endocrine glands. As endocrine glands, they secrete hormones that regulate the female reproductive system and influence broader bodily functions.
Ovarian Anatomy and Location
The ovaries are small, oval-shaped glands, about the size and shape of an almond. Each ovary measures approximately 3.5 to 4 centimeters in length, 2 centimeters wide, and 1 centimeter thick during a woman’s reproductive years. They are located within the pelvic cavity, positioned on either side of the uterus in shallow depressions known as ovarian fossae. Ligaments, such as the ovarian ligament, hold them in place, connecting them to the uterus and the pelvic wall.
Internally, each ovary is divided into two regions: an outer cortex and an inner medulla. The cortex contains numerous ovarian follicles, which house immature egg cells (oocytes), giving it a denser and more granular appearance. The inner medulla consists of loose connective tissue rich with blood vessels, lymphatic vessels, and nerves. The ovary is covered by a dense connective tissue capsule, the tunica albuginea, beneath an outer layer of cuboidal epithelium.
Egg Development and Ovulation
Females are born with their entire lifetime supply of oocytes, which are immature egg cells. At birth, a female’s ovaries contain approximately 1 to 2 million oocytes, each enclosed within a follicle. Many of these oocytes degenerate before puberty, leaving 300,000 to 400,000 by reproductive age. This finite number of eggs constitutes the ovarian reserve, which continuously declines throughout a woman’s life.
During each menstrual cycle, a cohort of primordial follicles begins to mature under the influence of follicle-stimulating hormone (FSH) from the pituitary gland. Typically, only one of these follicles becomes dominant and fully matures, a process that can take nearly a year from its initial recruitment. As the dominant follicle grows, it produces estrogen, which signals the pituitary to reduce FSH and luteinizing hormone (LH) levels until a specific threshold is reached. A sudden surge in LH then triggers ovulation, the release of the mature egg from the dominant follicle and expulsion from the ovary, around day 14 of a 28-day cycle. The released egg is then captured by the fimbriae of the nearby fallopian tube for potential fertilization.
Hormone Production and Its Effects
The ovaries serve as endocrine glands, primarily producing two steroid hormones: estrogen and progesterone. Estrogen, particularly estradiol, is the predominant form during reproductive years and plays a broad role in female physiology. It is responsible for the development of female secondary sex characteristics during puberty, including breast development, widening of the hips, and characteristic fat distribution. Estrogen also stimulates the growth and maturation of the uterus and vagina.
Progesterone, often referred to as the “hormone of pregnancy,” works in conjunction with estrogen to regulate the menstrual cycle. After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone. Progesterone’s main function is to prepare the uterine lining (endometrium) for the potential implantation of a fertilized egg by causing it to thicken and become more vascular. If pregnancy occurs, progesterone levels remain elevated, supporting early pregnancy and preventing further ovulation. Beyond reproduction, these hormones also influence bone formation, metabolism, and even brain function.
Changes During the Female Lifespan
The ovaries undergo significant changes throughout a female’s life. In childhood, the ovaries are dormant, with oocytes housed within primordial follicles awaiting activation. Some follicular development occurs, but it does not typically lead to ovulation or significant hormone production.
Puberty marks the activation of ovarian function, beginning between ages 8 and 13, driven by hormonal signals from the brain. This period sees the onset of regular menstrual cycles, mature egg release, and sex hormone production that facilitates reproductive capability. The reproductive years, from puberty until around age 50, are characterized by cyclic ovulation and hormone production. Fertility peaks in the twenties and gradually declines, with a more rapid decrease observed after age 37.
The female reproductive lifespan culminates in menopause, the natural cessation of ovarian function. This occurs around the age of 51, though it can range from 40 to 55 years. During menopause, the remaining ovarian follicles are depleted or no longer respond to hormonal signals, leading to the end of egg release and a significant decline in estrogen and progesterone production. This hormonal shift results in the cessation of menstruation and the end of reproductive capacity.