The human ovary is an important organ within the female reproductive system. These small, paired glands serve a dual purpose: producing eggs and synthesizing various hormones. Their proper functioning is essential for reproductive health and influences various bodily processes. Understanding the roles of the ovaries provides insight into female biology and overall well-being.
Anatomy and Location
The ovaries are small, ovoid structures, often described as almond-shaped. They have a whitish or grayish color and an uneven surface. These organs are situated within the female pelvic cavity, positioned on either side of the uterus in shallow depressions known as ovarian fossae.
They are held in place by ligaments, including the ovarian ligament connecting them to the uterus, and the suspensory ligament to the pelvic wall. Internally, each ovary is composed of two main regions: an outer cortex and an inner medulla. The cortex contains numerous ovarian follicles at various stages of development, while the medulla is made of loose connective tissue rich in blood vessels, lymphatic vessels, and nerve fibers.
Producing Eggs
The ovaries produce and release eggs, a process called oogenesis. This process begins before birth, with millions of immature germ cells, called oogonia, forming within the fetal ovaries. These develop into primary oocytes, encased in primordial follicles.
At birth, ovaries contain 1 to 2 million primordial follicles, each holding a primary oocyte arrested in an early stage of meiosis. At puberty, a small group of these follicles are recruited each menstrual cycle to mature. Most developing follicles undergo atresia, a process of degeneration, with usually only one fully maturing.
The selected follicle progresses through stages: primary, secondary, and finally a tertiary, or Graafian follicle. Within the mature Graafian follicle, the primary oocyte completes its first meiotic division, resulting in a secondary oocyte and a polar body. Ovulation then occurs, as the mature Graafian follicle ruptures, releasing the secondary oocyte into the fallopian tube for potential fertilization.
Hormone Production
The ovaries also function as endocrine glands, synthesizing and secreting hormones that regulate various bodily functions. The main female sex hormones produced are estrogen (primarily estradiol during reproductive years) and progesterone. These hormones are generated by developing follicles and, after ovulation, by the corpus luteum, a temporary glandular structure formed from the ruptured follicle.
Estrogen plays many roles, including developing female secondary sexual characteristics like breast development, widening of the pelvis, and the growth of pubic and underarm hair during puberty. It also regulates the menstrual cycle by promoting uterine lining thickening, and influences bone density and cardiovascular health. Progesterone works alongside estrogen, especially after ovulation, to prepare the uterus for potential pregnancy.
Progesterone helps stabilize the menstrual cycle and maintains the uterine lining, making it receptive for embryo implantation. If pregnancy occurs, progesterone levels remain high, supporting the uterine environment and decreasing uterine muscle contractions to sustain gestation. Both hormones contribute to reproductive system health and impact various physiological systems throughout a woman’s life.
Ovarian Changes Over a Lifetime
Ovarian function and structure transform across a woman’s lifespan, reflecting different reproductive stages. At birth, ovaries contain a lifetime supply of eggs, approximately 1 to 2 million primordial follicles. By puberty, this number decreases to 300,000 to 500,000 as many follicles naturally degenerate.
During reproductive years (from puberty until perimenopause), ovaries regularly engage in cyclic activity, maturing and releasing an egg each month, alongside consistent hormone production. This period features predictable menstrual cycles and peak fertility. Around 400 eggs are ovulated, while the vast majority of the initial egg reserve undergoes atresia.
As a woman approaches perimenopause (usually in her 40s), ovarian function declines. Remaining egg reserves diminish, and egg quality can decrease, leading to irregular menstrual cycles and reduced likelihood of natural conception. This transition culminates in menopause, defined as 12 consecutive months without a menstrual period. This indicates near depletion of ovarian follicles and a significant drop in ovarian hormone production.