[Anatomy and pathophysiology of hemorrhoids].

The internal (hemmorrhoidal) plexus consists of two groups of veins separated by the musculus canalis ani. The submucosal group forms the zona hemorrhoidalis. A direct communication between arteries and veins is the characteristic sign of this functional part of rectal circulation. In the nutrient part, the arterioles divide into capillaries. The vessels of the zona hemorrhoidalis are wrapped in by a system of elastic fibers, which split with age. Common pathogenetic factors of hemorrhoids may involve the spasm of anal sphincters and the absence of elastic fiber support of the plexus.