The venous valves of the lower limbs

description of the anatomy of valves and microvalves in the veins of the lower limb Venous valves appear after the heart begins to beat and the primordial muscles begin to move the limb buds. The pressure gradient due to heart beats and muscle movements triggers the process of venous valve development. Prenatal, postnatal, and senile morphological and numerical rearrangements have been described. However, the signaling pathways related to venous valve morphogenesis have yet to be clearly demonstrated. The cusps of the venous valves consist of thin collagen half-moon–shaped folds covered by endothelium, which spring from the wall of the vein very close to each other. The vein wall is thicker at the base of the valve cusps, due to an increase in the number of smooth muscle cells in the media. With increasing age, the loose areolar collagen stroma of the cusp is gradually replaced by thick and fibrous tissue. This article first describes the distribution of the valves in the deep, superficial, and perforating veins of the lower limbs. Finally, the morphology and location of valves in the microveins and their possible role in the pathogenesis of skin changes related to venous insufficiency are described.