Uterus and Menstrual Cycle

Female Reproductive System

The uterus

Female Reproductive System
The uterus consists of muscle and an inner endometrial lining that responds to the ovarian hormones estrogen and progesterone.

The uterus is a pear-shaped muscular organ in the upper female reproductive tract. The uterine fundus is the upper portion of the uterus where pregnancy occurs. The cervix is the lower portion of the uterus that connects with the vagina and serves as a sphincter to keep the uterus closed during pregnancy until it is time to deliver a baby. The fallopian tubes extend from the sides of the uterine fundus toward the ovaries. The function of the fallopian tubes is to capture an egg at the time of ovulation, allow the sperm and egg to meet so that fertilization will occur, and to nourish and transport the fertilized egg to the uterus at the right time for implantation.

The main body of the uterus consists of a firm outer coat of muscle (myometrium) and an inner lining of vascular, glandular material (endometrium). The endometrium thickens during the menstrual cycle to allow implantation of a fertilized egg. Pregnancy occurs when the fertilized egg implants successfully into the endometrial lining. If fertilization does not occur, the endometrium sloughs off and is expelled as menstrual flow. This cyclic process – the menstrual cycle – results from the interaction between the female reproductive organs and the endocrine system.

Hormones and the menstrual cycle

Menstrual Cycle
Estrogen and progesterone regulate the growth and shedding of the endometrium, resulting in the menstrual cycle.

The female hormones that control the cyclic growth and shedding of the endometrium are estrogen and progesterone. Estrogen and progesterone are produced by the ovaries. Estrogen causes the growth or proliferation of the endometrium during the first 2 weeks of the menstrual cycle. After ovulation, the ovary produces progesterone. This hormone causes the endometrial glands to secrete nutritive substances required by the embryo and to allow it to implant into the endometrial lining.

If fertilization and implantation do not occur, the progesterone falls and the endometrial lining is sloughed off - resulting in menstrual bleeding. If fertilization and implantation do occur, then the ovary continues producing progesterone and the endometrium remains intact to support embryo development and pregnancy.

More information is available about the uterus on the Tubal Reversal web site.

Female Reproductive System

Ovaries and Ovulation

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