Arrangement of Muscle Fibers in the Myometrium of the Human Uterus: A Mesoscopic Study

Abstract

The human uterus is a hollow, thick-walled and contractile organ with the purpose of receiving the product of fertilization along with its nesting, growth and subsequent birth. Part of its function is made possible due to its muscular layer, traditionally described as consisting of three layers or strata: an outer layer of predominantly horizontal and then longitudinal fibers; a middle layer comprised of circular fibers arranged in multiple directions containing a layer of blood vessels; and an inner layer of similar structure to the outer layer. This study aims to describe the mesoscopic way in which the muscle fibers of human uterine myometrium are arranged. 10 samples of bisected human uteri were investigated. The results following dissection first showed the perimetrium under a lower layer of longitudinal fiber followed by horizontal fibers that, as they approach the margin, become skewed in the direction of the oviducts. Also, a small amount of fibers that change from horizontal to longitudinal near the median plane were found to pass through the middle region of the body of the uterus. Beyond the deep plane, we found fibers arranged in multiple directions, resembling eddies that are directed at an angle from the outside inwards and mark the location of small blood vessels. In the deepest part, we found a thin layer containing few horizontal fibers.