Endocrine Community. Email Print Discuss. Written by Robert M. Sargis MD, PhD.
Where are the ovaries?
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. 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.
Ovaries produce and release two groups of sex hormones—progesterone and estrogen. There are actually three major estrogens, known as estradiol, estrone, and estriol.
Understanding the Function of Your Ovaries
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.
Early in fetal development, primitive germ cells in the ovaries differentiate into oogonia. These divide rapidly to form thousands of cells, still called oogonia, which have a full complement of 46 23 pairs chromosomes. Oogonia then enter a growth phase, enlarge, and become primary oocytes. The diploid 46 chromosomes primary oocytes replicate their DNA and begin the first meiotic division, but the process stops in prophase and the cells remain in this suspended state until puberty.
Many of the primary oocytes degenerate before birth, but even with this decline, the two ovaries together contain approximately , oocytes at birth. This is the lifetime supply, and no more will develop. This is quite different than the male in which spermatogonia and primary spermatocytes continue to be produced throughout the reproductive lifetime.
By puberty the number of primary oocytes has further declined to about , Beginning at puberty , under the influence of follicle-stimulating hormone , several primary oocytes start to grow again each month. One of the primary oocytes seems to outgrow the others and it resumes meiosis I. The other cells degenerate. The large cell undergoes an unequal division so that nearly all the cytoplasm , organelles, and half the chromosomes go to one cell, which becomes a secondary oocyte.
The remaining half of the chromosomes go to a smaller cell called the first polar body. The secondary oocyte begins the second meiotic division, but the process stops in metaphase.
At this point ovulation occurs. If fertilization occurs, meiosis II continues. Again this is an unequal division with all of the cytoplasm going to the ovum, which has 23 single-stranded chromosome. The smaller cell from this division is a second polar body. The first polar body also usually divides in meiosis I to produce two even smaller polar bodies. They can invade nearby tissues and break off from an initial tumor to spread elsewhere in the body metastasize. The type of cell where the cancer begins determines the type of ovarian cancer you have.
Enlarged ovaries: Symptoms, causes, and treatment
Ovarian cancer types include:. Inherited gene mutations. A small percentage of ovarian cancers are caused by gene mutations you inherit from your parents. These genes also increase the risk of breast cancer. Other gene mutations, including those associated with Lynch syndrome, are known to increase the risk of ovarian cancer. Ovarian cancer care at Mayo Clinic.
Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. This content does not have an English version.
- Text Bullying - Is Your Child Being Bullied Online (77 Ways to Parent Series Book 2).
- Ovary - Wikipedia.
- The ovary: basic biology and clinical implications..
- Understanding What the Ovaries Do.
- Understanding the Function of Your Ovaries!
- Navigation menu?
- Ovaries | You and Your Hormones from the Society for Endocrinology;
This content does not have an Arabic version. Ovarian cancer Ovarian cancer is a type of cancer that begins in the ovaries. Female reproductive system The ovaries, fallopian tubes, uterus, cervix and vagina vaginal canal make up the female reproductive system. Request an Appointment at Mayo Clinic. Share on: Facebook Twitter. References AskMayoExpert.
Ovarian cancer. Rochester, Minn. Lobo RA, et al. Neoplastic diseases of the ovary.