Excessive strain in the rectal area may not go too well with the veins situated in the anal cavity. When these veins are exposed to too much pressure, the outcome is hemorrhoids. The veins inside the lower rectal area are delicate and hence are not equipped to handle extra pressure. The excess strain restricts blood circulation from the veins to the heart. This reduces blood flow to the heart, cuts down oxygen supply to the veins, leading to swelling. The swollen veins in the anus have often been associated with irregular bowel movement.