<< View all animations

A woman is born with all of the egg cells she will release throughout her lifetime. Starting at about age 12 through menopause, a woman's reproductive cycle releases an egg about once a month.

Hormonal messages from the brain instruct the ovaries to develop several follicles in which a single dominant follicle in one of the ovaries will release an egg for fertilization. During this time, other hormones instruct the uterine lining to thicken in preparation for nourishing a fertilized egg.

There are several hormones that regulate the reproductive cycle. Follicle stimulating hormone (FSH) stimulates preparation of the egg for fertilization by instructing a follicle to begin dividing it's genetic material (chromosomes).

The follicle then releases estrogen, the hormone that prepares the lining of the uterus to receive a fertilized egg. Increased levels of estrogen in the bloodstream cause a small structure in the brain, the pituitary gland, to stop releasing the hormone FSH, and to start releasing luteinizing hormone (LH).

LH causes the follicle to enlarge rapidly and to release its egg in a process known as ovulation. Once the egg is out of the follicle, the follicle begins secreting the hormone progesterone, which also helps to prepare the uterine lining for the fertilized egg. The remaining cells of the follicle shrink into a hormone producing mass of cells called a corpus luteum.

The egg is swept into the fallopian tube by its waving structures called fimbriae. Fertilization of the egg usually occurs in the fallopian tube. From there, it is transported to the uterus and implants itself in the uterine wall, where it is nourished by the uterine lining. In the ovary, the corpus luteum produces progesterone so that the egg can develop into a fetus.

If the egg is not fertilized within 24 hours after its release from the ovary, it stops developing and dissolves before reaching the uterus. The absence of a fertilized egg causes the body to stop releasing the hormones that prepare the uterus for implantation. In response, the uterus sheds its lining over a period of four to five days in a process known as menstruation.

	Need an appointment? Request one online 24 hours/day, 7 days/week or call 800-789-PENN (7366) to speak to a referral counselor.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial process. A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

©Copyright 2005 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites.