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.

The In Vitro Contractile Response of Canine Pregnant Myometrium to Oxytocin and Denaverine Hydrochloride

“…This separation of myometrial layers has not been previously described for dogs, but it was performed with guinea pig uterine tissue [58][59][60]. In human myometrium, the "mesh"-like microstructure [61] does not allow for separation, thus, explaining the lack of functional studies on separate myometrial layers in women so far [62]. Accordingly, in organ bath studies, the human myometrium is cut along the muscle fibers running parallel to the longitudinal axis of the uterus [49,52,63,64].…”

Current status and challenges in uterine myometrial tissue engineering

“…The inner and outer myometrial layers are mostly associated with the initial layers of the paramesonephric ducts, with fibers arranged in longitudinal, crisscross and circular directions, respectively as shown in Figure 1 . The middle intermediate layer contributes to the uterine thickness with many blood vessels providing nutritional and nervous supply [ 7 ]. Actin and myosin proteins interact to help with uterine contraction by electrical coupling, with changes in extracellular and intracellular calcium transport aiding depolarization and action potential.…”

Neural plasticity of the uterus: New targets for endometrial cancer?

“…Finally, the outer layer is known as the serosa and is composed of epithelial cells. Regarding vascularization, arcuate vessels originating from anastomoses of uterine and ovarian vessels penetrate the myometrium in a spiral-shape and branch into radial arteries that traverse the myometrium to arrive at the endometrium as spiral arteries 18 (Figure 1(b)).…”