Definition - What does Myometrium mean?

The myometrium is the smooth muscle wall of the uterus. It contracts during menstruation to expel shed endometrial lining from the uterus. During labor, the myometrium performs much stronger contractions to facilitate birth. Its densely cross-linked structure make it one of the strongest muscles in the body. Fibroids—a common, noncancerous uterine growth—are growths of the myometrial tissue. Fibroids can cause pain as well as fertility problems, although many women have fibroids without experiencing infertility.

FertilitySmarts explains Myometrium

The uterus consists of three layers of tissue:

  • The innermost, the endometrium, creates the uterine lining which nurtures developing fetuses and is shed in each menstrual cycle if conception does not occur.
  • The myometrium surrounds the endometrium and assists with menstruation and labor by contracting in waves to expel the contents of the uterus.
  • The outermost layer is the perimetrium, a skin-like membrane that separates the uterus from other organs.

The myometrium is composed of smooth muscle cells, similar to the muscles of the digestive tract and circulatory system. Unlike skeletal muscle, smooth muscle does not rely on commands from the brain to contract. Instead, the nerves within smooth muscle tissue create automatic, rhythmic contractions.The smooth muscle of the myometrium responds to several different chemical messengers that help to regulate its role in labor and menstruation.

To bring about menstruation, hormones, as well as chemicals released by the breakdown of endometrial tissue, stimulate the innermost layer of the myometrium to contract. These contractions squeeze the blood vessels that feed the endometrium closed, contributing to the further breakdown of the endometrial lining. As breakdown continues, the contractions become stronger and expel the unused endometrial tissue in the process of menstruation.

These myometrial contractions to stimulate breakdown and expulsion of the endometrium may cause premenstrual cramps.

During labor, all layers of the myometrium contract to produce the very powerful contractions which push the baby out of the uterus. The middle and outer layers of the myometrium are much stronger than the innermost layer, which is activated during menstruation.

Adenomyosis is a condition where cells from the uterine lining break through the muscle wall of the myometrium.


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