What is the Myometrium?
The myometrium is the thick, muscular middle layer of the uterine wall. It's primarily composed of smooth muscle cells, but also includes supportive stromal and vascular tissue. Think of it as the powerful engine of the uterus, responsible for the contractions during menstruation and childbirth.
The myometrium plays a crucial role in several key functions:
- Menstruation: The myometrium contracts to shed the uterine lining during menstruation.
- Pregnancy: Its powerful contractions help expel the baby during labor.
- Uterine Growth and Development: The myometrium's structure and function change throughout a woman's reproductive life, adapting to hormonal changes and pregnancy.
The myometrium's smooth muscle cells are influenced by various factors including hormones like oxytocin and prostaglandins. These hormones trigger contractions during labor and menstruation. Growth factors also modulate the growth, proliferation, and differentiation of the myometrial cells. (https://pmc.ncbi.nlm.nih.gov/articles/PMC3191937/)
Myometrium and Uterine Conditions
Several uterine conditions affect the myometrium:
- Adenomyosis: This condition involves the growth of endometrial tissue into the myometrium, causing the uterus to thicken and enlarge, often leading to painful periods and heavy bleeding. (https://my.clevelandclinic.org/health/diseases/14167-adenomyosis, https://www.hopkinsmedicine.org/health/conditions-and-diseases/adenomyosis)
- Uterine Fibroids: These benign tumors can grow within the myometrium, sometimes causing pain, heavy bleeding, and infertility.
- Uterine Cancer: The extent of myometrial invasion is a key factor in determining the stage and prognosis of uterine cancer. (https://cancer.ca/en/cancer-information/cancer-types/uterine/prognosis-and-survival)
Layers of the Uterus
The uterus has three distinct layers:
- Perimetrium: The outer, serous layer.
- Myometrium: The thick, muscular middle layer.
- Endometrium: The inner lining, which sheds during menstruation. (https://www.cancer.gov/publications/dictionaries/cancer-terms/def/myometrium, https://cancer.ca/en/cancer-information/cancer-types/uterine/what-is-uterine-cancer/the-uterus)
The myometrium’s structure is complex, with an outer layer, a dense network of fibers, and an inner layer. (https://www.sciencedirect.com/topics/medicine-and-dentistry/myometrium) Sonographic imaging helps visualize and assess the myometrium and any lesions within it. (https://obgyn.onlinelibrary.wiley.com/doi/10.1002/uog.14806, https://www.ncbi.nlm.nih.gov/books/NBK585034/)
