[Histophysiology of the uterine isthmus]

The uterine isthmus is morphologically defined as a topographic zone between the uterine corpus and the cervix, in very close association with the vasomusculary afferences. Architecturally isthmus corresponds to the connective-muscular function which is different by its thickness (from 2 mm to 10 mm) and by its morphology (digited, undulating sharp and regular). Histologically isthmus is made up by collagen fibers myometrial muscle cells, irregularly directed. The relationship of these two components reveal their functional synergy between the predominance of the connective tissue and the weakners of the muscle cells. The specific function of the isthmus and its autonomy depend: of the type and direction of the collagen fibers, and the quantity and arrangement the muscle cells, of the biochemical modifications and the variability of the ground substance moreover of the relations with the nervovascular endings. The isthmus incontinence is associated with these structural anomalies (muscular components, elastic fibers defects, connective tissue pathology, activity of the nerve endings, enzymatic troubles under hormonal control).