Haemorrhoids arise from the anal cushions in the upper part of the anal canal. These cushions play an important role in closing the anal canal and promoting continence. The cushions receive arterial blood from the terminal branches of the superior rectal arteries with some input from the middle and inferior rectal arteries. There are several small arterio-venous connections and the veins form saccules in the cushions.
There are usually three main cushions, two on the right and one on the left. They are arranged around the clock (Anterior is 12, posterior 6, right 3 and left 9) at the 4 o'clock, 7 o'clock and 11 o'clock positions.