Bleeding haemorrhoids. Colonoscope (endoscope) view of bleeding haemorrhoids (piles) in a patient's rectum. This is a retroflexed (bent backwards) view of rectum, the endoscope (black) is also seen. Haemorrhoids are swollen veins in the lining of the rectum, the final part of the large intestine. They are caused by increased pressure in these veins, usually due to the patient straining to expel hard faeces. They cause pain and bleeding on defecation. A diet high in fibre and fluids can help reduce their severity, and anti-inflammatory drugs can reduce the swelling. Severe cases may require surgical treatment.