Uterine fibroids are non-cancerous growths that develop within the uterus, impacting many individuals during their reproductive years. These growths often cause heavy menstrual bleeding, also known as menorrhagia. This article explores the biological reasons why fibroids contribute to excessive bleeding.
What Are Fibroids?
Fibroids, also called leiomyomas or myomas, are benign growths composed of muscle and connective tissue that form in or on the wall of the uterus. They can vary significantly in size, from as small as a seed to as large as a melon. While some individuals with fibroids experience no symptoms, their location and size often determine the impact they have on uterine health.
Fibroids are typically categorized by their location within the uterus. Intramural fibroids are the most common type, growing within the muscular wall of the uterus. Submucosal fibroids develop just beneath the inner lining of the uterus and protrude into the uterine cavity. This specific type is particularly associated with heavy bleeding, even at smaller sizes, due to its proximity to the endometrial lining.
How Fibroids Affect Uterine Function
Fibroids alter the uterus’s structure and function, leading to heavier menstrual flow. Large fibroids can distort the overall shape and enlarge the uterus. This enlargement can increase the surface area of the endometrium, the uterine lining that is shed during menstruation. A larger endometrial surface means more tissue and blood vessels are shed, leading to increased bleeding.
Fibroids can also exert pressure on the uterine cavity and blood vessels. This pressure can interfere with the normal contraction of the uterine muscles (myometrium). During menstruation, these contractions compress blood vessels and reduce blood flow after the lining sheds. When this process is impaired, bleeding can become prolonged and heavier.
Specific Biological Mechanisms of Heavy Bleeding
Several specific biological mechanisms contribute to the heavy bleeding experienced by individuals with fibroids. Submucosal fibroids, growing into the uterine cavity, increase the endometrial surface area. This expanded surface means more tissue is shed, leading to greater blood loss. Even small submucosal fibroids can cause substantial bleeding due to their direct impact on the lining.
Fibroids can also lead to the development of abnormal blood vessels within the uterine wall and lining. These vessels may be dilated, fragile, or leaky, making them prone to rupture and excessive bleeding. Fibroids can also impair the uterus’s ability to contract. Normal uterine contractions constrict blood vessels and reduce blood flow after the lining sheds. When fibroids interfere with these contractions, blood vessels may remain open, resulting in prolonged and heavier menstrual flow.
Fibroids can foster a local inflammatory environment within the uterus. This inflammation involves molecules like cytokines and prostaglandins, influencing blood vessel dilation and clotting. An imbalance in these factors can contribute to increased blood loss and prolonged bleeding. Hormonal influences, particularly estrogen and progesterone, also play a role in fibroid growth and uterine bleeding.