Hemorrhoids occur when vascular tissue, a vein or other blood bearing part of the
circulatory system, becomes swollen and develops a sac or bulb. When you have a
bowel movement, blood is moved to the rectum and colon to aid in the proper muscular
function of the lower digestive tract. Although this is normal, when the patient strains
or pushes, they may push increased blood flow to the veins in and around the anus,
causing the veins to stretch. Veins then have the ability to accommodate additional
blood and hemroids form. Similarly, if you have diarrhea or constipation which causes
straining during bowel movements, hemorrhoids can form.