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An Overview of the Ovaries

Estrogen, Progesterone, and Reproduction

Ovaries Essentials

  • The ovaries maintain the health of the female reproductive system.
  • They secrete two main hormones—estrogen and progesterone.
  • Diseases associated with the ovaries include ovarian cysts, ovarian cancer, menstrual cycle disorders, and polycystic ovarian syndrome.
The ovaries are a pair of ova-producing organs (that is, they produce egg cells) that maintain the health of the female reproductive system. The ovaries, like their male counterpart, the testes, are known as gonads. This simply means they are the primary reproductive organs.

In addition to their role in producing ova, the ovaries also have the distinction of being an endocrine gland because they secrete hormones—primarily estrogen and progesterone—that are vital to normal reproductive development and fertility.

Anatomy of the Ovaries
The ovaries are oval shaped and about the size of a large grape. They are located on opposite ends of the pelvic wall, on either side of the uterus. The ovaries are each attached to the fimbria (tissue that connects the ovaries to the fallopian tube).
Hormones of the Ovaries
Ovaries produce and release two groups of sex hormones—progesterone and estrogen. There are actually three major estrogens, known as estradiol, estrone, and estriol. These substances work together to promote the healthy development of female sex characteristics during puberty and to ensure fertility.
Estrogen (estradiol, specifically) is instrumental in breast development, fat distribution in the hips, legs, and breasts, and the development of reproductive organs.
To a lesser extent, the ovaries release the hormone relaxin prior to giving birth. Another minor hormone is inhibin, which is important for signaling to the pituitary to inhibit follicle-stimulating hormone secretion.
Progesterone and Estrogen Production and Function
Progesterone and estrogen are necessary to prepare the uterus for menstruation, and their release is triggered by the hypothalamus.
Once you reach puberty, the ovaries release a single egg each month (the ovaries typically alternate releasing an egg)—this is called ovulation. The hypothalamus sends a signal to the pituitary gland to release gonadotrophic substances (follicle stimulating hormone and luteinizing hormone). These hormones are essential to normal reproductive function—including regulation of the menstrual cycle.
As the egg migrates down the fallopian tube, progesterone is released. It is secreted by a temporary gland formed within the ovary after ovulation called the corpus luteum. Progesterone prepares the body for pregnancy by causing the uterine lining to thicken. If a woman is not pregnant, the corpus luteum disappears.
If a woman is pregnant, the pregnancy will trigger high levels of estrogen and progesterone, which prevent further eggs from maturing. Progesterone is secreted to prevent uterine contractions that may disturb the growing embryo. The hormone also prepares the breasts for lactation.
Increased estrogen levels near the end of pregnancy alert the pituitary gland to release oxytocin, which causes uterine contractions. Before delivery, the ovaries release relaxin, which as the name suggests, loosens the pelvic ligaments in preparation for labor.
More hormones are released during pregnancy than at any other time of a woman’s life, but during menopause—which marks the end of fertility—estrogen levels fall fast. This can lead to a range of complications. 
Diseases and Disorders of the Ovaries
  • Osteoporosis: Osteoporosis is commonly associated with menopause, just like mood swings and hot flashes.


    Menopause is marked by the rapid loss of estrogen. The role estrogen play in bone loss can best be described in terms of a battle between osteoclasts (bone absorbing cells) and osteoblasts (bone producing cells). Estrogen is on the side of the osteoblasts, but as the estrogens diminish, the osteoblasts are discouraged from producing more bone. As such, the osteoclasts win by absorbing more bone than is being produced by the osteoblasts.

    Estrogen replacement therapy during menopause protects bone mass and helps protect against the risk of osteoporotic fractures.

  • Ovarian Cancer: Ovarian cancer is an extremely serious, but rare, disease. Its symptoms usually don’t become apparent until the cancer has progressed into the later stages.

    Symptoms of ovarian cancer include: persistent abdominal pain, indigestion, bloating, abnormal uterine bleeding, and pain during sexual intercourse. These are common problems, so in the great majority of cases, they will not indicate cancer. However, it’s important you pay attention to your body and discuss anything out of the ordinary—no matter how insignificant you think it may be—with your doctor.
  • Ovarian Cysts: Ovarian cysts are fluid-filled sacs that affect women of all ages, though mostly women of child-bearing age. Cysts are very common—and they can range in size from a pea to a grapefruit. The majority of cysts are harmless, though larger cysts (those larger than 5 cm in diameter) may need to be surgically removed because large cysts can twist the ovary and disrupt its blood supply.

    Cysts can form for a variety of reasons. Oftentimes, they’re simply part of normal menstruation. You may experience no symptoms, and the cysts will go away after a few cycles. These are known as functional cysts.

    The great majority of cysts are benign. But abnormal or pathological cysts, such as those in polycystic ovary syndrome (PCOS), may cause painful symptoms.

    Treatment for ovarian cysts depends on the size and type of cyst. If you’re experiencing pain, talk to your doctor. He or she will determine what treatment is best for you.

    Below are some common symptoms of pathological cysts:

    • The most telltale symptom is pain and discomfort in the abdomen, vagina, low back, or thighs
    • Breast tenderness
    • Bloating
    • Increased hair growth on your face, back, and chest
    • Pain before or after your menstrual cycle and irregular periods
    • Infertility
    • Weight gain
    • Fatigue
  • Polycystic Ovary Syndrome: Polycystic means “many cysts.” Interestingly, the National Institutes of Health (NIH) criteria for diagnosing PCOS do not require the presence of polycystic ovaries by pelvic ultrasound. The NIH criteria are based on signs of hyperandrogenism (or elevated androgens) and oligo/amenorrhea.  Other key characteristics include infertility, irregular menstruation, acne, and increased hair growth on the face and body.

    PCOS is essentially caused by a hormone imbalance—many of the symptoms are caused by increased production of androgens. These patients usually have high free testosterone levels.

    It’s not uncommon for those diagnosed with PCOS to be overweight, insulin resistant, and have type 2 diabetes. Many of the symptoms of PCOS fade with weight loss.
The ovaries have an immensely important role not only in the female reproductive system but in the endocrine system as a whole. The hormones they secrete ensure the proper development of the female body and promote healthy fertility.



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