in the body there are parts that have double circulation.This means blood supply from two different circulatory systems.
The four different circulatory systems are:
1.splanchnic or general circulation of blood in the muscle and bones of the body.
2.The visceral circulation meaning the circulation of blood in the viscera.portal hepatic circulation is a typical example.Pulmonary circulation in the lungs as well as cerebral circulation in the brain are the other visceral circulations.
The anal canal has a meeting of both the porto-hepatic visceral circulation and the splanchnic circulation at the anal valves which cause pile or haemmorrhoid conditions.