health

The endometrium (en-do-ME-tree-um) is the lining of the uterus,
which is the muscular organ where a fetus develops during pregnancy.
Endometriosis is a condition in which endometrial tissue implants and
grows outside the uterus. During the monthly menstrual cycle, chemicals
called hormones cause the endometrium to grow thick in preparation
for receiving a fertilized egg at the beginning of pregnancy. If the egg
is not fertilized, there is no pregnancy and the endometrium is shed as
blood and tissue in the monthly menstrual period.
In a woman with endometriosis, fragments of endometrial tissue
develop outside the uterus. The cause of endometriosis is not fully understood.
There are several theories. Some scientists think that some of the
endometrial tissue that should leave the body during menstruation does
not. Instead, these stray fragments find their way into other parts of the
pelvic cavity. Here the stray pieces of tissue attach to other organs such
as the ovaries or intestines, stick organs together, or form scar tissue.
Scientists theorize that there may be a genetic predisposition (inherited
tendency) toward developing endometriosis. Research ongoing as of
2009 sought to determine if stray tissues develop in some women because
their immune systems, which normally destroy any unexpected material
such as stray endometrium, do not function efficiently. In addition, some
scientists were exploring whether exposure to human-made chemicals
found in the environment may trigger endometriosis in some women.
Estimates as of 2007 suggested that between 2 and 10 percent of women
or 5.5 million women in North America have endometriosis.